My New "Cheap Astronomy" Blog

I started a "Cheap Astronomy" Blog and will be posting new astronomy related content on that blog! Have fun!

Cheap Astronomy – Ancient Wisdom

A man can't stand, he can't fight. A man can't breathe, he can't fight. A man can't see, he can't fight.
-- The Karate Kid, Part III

In the matter of hand-to-hand combat (in which I have no experience, thankfully) one needs three things according to ancient wisdom:

• Being able to stand
• Being able to breathe
• Being able to see

Or maybe not ancient wisdom, this is at least according to the motion picture "The Karate Kid, Part III", which I have not seen seen (and can furthermore not vouch to its authoritativeness on the matter of hand-to-hand combat).

But it reminded me of basically three areas you need to do visual astronomy (to paint a very simplified picture):

• Optics, seeing and eyes, to be able to see
• Some sort of mount, for stability
• And "usability"

Well, the first point should be plain and obvious: if you can't see, you can't do astronomy. While the area of optical quality of the telescope is most accessible to objective measurement, it is not something that can be put into one number. There is too many things to know beyond aperture and f-ratio: MTF, contrast, stray light reduction, field of view (or rather field of view free of mechanical vignetting), chromatic aberration, spheric aberration, coma, astigmatism, field curvature, distoration, RMS wavefront error, Strehl ratio, and so on. (And that is not accounting for tolerances and errors during production…) But at least one can try to get a measured idea of what to expect from a scope.

Another point not on the radar for beginners: To be able to see is more than just the quality of "optical tube assembly" (and more than the combination of OTA with eyepieces). Unfortunately this is a topic of its own.

The second point is usually overlooked as well by inexperience beginners (and exploited by the industry sell them undersized mounts): One is using high magnifications and any shaking caused by a mount will make it hard (if not impossible) to use an astronomical telescope. There is the measure of maximum telescope weight supported by an mount, but (beyond the question of how this is measured) this is not a simple number or measurement: A long telescope will put more strain on a mount than a short telescope with the same weight. Person A is more tolerant to shaking than person B. And so on. But it stands: The more stable a mount, the more enjoyable a view through a scope.

And while the third point seems simple (to the point of being a tautology), it is the hardest to grasp: If an telescope setup lacks usability, it is not usable. If you can't find things in the night sky with it, what good is a telescope? What good is a telescope and mount, if it is so heavy that you rather leave it at home than drag it with you? What good are high magnifications if the focuser shifting is so bad that you can't actually reach focus?

Now if it were just "Good, But Expensive Astronomy" I'm after, I would recommend the best setup that money can buy (and there are some out there).  Some of these question can be solved by throwing money at them. But only up to a point.

If you want to do astronomy, you have to invest time, acquire knowledge and skills – just like any other hobby, just like a craft or a sport. Sure you can have fun just "dabbling" in astronomy, but for me the fun in is improving, advancing, progressing.



And for me it is "Cheap Astronomy" I'm after, or rather affordable astronomy, with a good ratio of cost to optical quality, stability and usability. With some some measured modifications. Investing time to save money and gain knowledge.

More to follow.

Cheap Astronomy – Things That Are Free: Meteoblue's "Astronomical Seeing" Prediction

When I prepared myself for the Triple Conjuction, I had to drive to another site – so I wanted to know beforehand how the weather would be, and especially if there were clouds or not.

One thing I found mildly helpful was looking into nearby airports. I have two small airstrips near by, and both have some interesting weather information. One is military and has some cloud predictions, the other is a small private one with temperature and dew point record for the last 24h, plus current webcam images

Since then I tried to find a website which is more dedicated to weather in the context of astronomical seeing. Of course one immediately finds the "Clear Sky Chart" website and Weather Underground's Astronomy service – but unfortunately they cater mainly to the continental US and Canada.

I then searched some more and found the "Astronomical Seeing" service by Meteoblue. Until now I have mainly used their cloud prediction and found it to be quite reliable.They have many more features (like "seeing"), and I hope to utilize them in the future – but I am neither proficient enough nor have I used it other informtion to comment on the quality of their "seeing" information.

Sow what else do they offer? They offer quite some information, with hourly resolution for three days. Most of it presented in color, so one can immediately grasp what one has to expect for the next days.

The Meteoblue information for the current day for a semi-randomly selected city in Russia – things like daytime/nighttime and cloudcover are immediately obvious. Notice the "mouse-over" with planet information in the lower right corner.

The information about astronomical weather they display is:

• Cloudcover (low, mid and high)
• Different seeing indices (different calculation methods)
• Jet stream and "bad" layers
• Temperature and humidity

Furthermore they show some information about our Solar System:

• Daily Sun rise and Sun set
• Daily Moon rise, Moon set and Moon phase (both as number and as text)
• Hourly information for visible planets* (with coordinates via "mouse over")

It is all presented very nicely and I usually look once a day to know if I should prepare for an astronomical session (or not).

*All eight planets except the Earth – duh – plus the dwarf planet Pluto.

Cheap Astronomy – Put Some Flock On Your Barlows!

I would have wanted to look at the Moon tonight, but the clouds are prohibitive today. So I played a bit around with an artificial target I have and to my horror found out that my Barlows were not useful for looking at bright targets. By now I have six Barlows and – with the sole exception of the "KSON 3x achromatic" – each and everyone had problems with internal reflections. Thankfully in each case the usefulness of the Barlow was hugely improved by putting flocking material on the cause of the internal reflection.

These are the Barlows I have now:

• 3x "long barrel" cheap plastic Barlow (0.965 inch)
• 2x all metal "Japan" Barlow (0.965 inch)
• 2x "shorty" cheap plastic Barlow with singlet glass lens (1.25 inch)
• 2x Knight-Owl Barlow (1.25 inch)
• 3x Knight-Owl Barlow (1.25 inch)
• 3x KSON achromatic Barlow (1.25 inch)

And as I said the KSON was the only one that did not need any modification. All the others had internal reflections that degraded contrast and made the image blurred. This was especially annoying when looking at the Moon, as the image became so "washed out" that the Barlows were useless – a child's marble would produce a better image.

What to do?

To check a Barlow, put the Barlow in the focuser (best to test in the fastest scope you have and do not put a eyepiece in), and then shine a flash-light in the scope: When looking into the Barlow, do you see any reflections? Flock 'em! Smoke 'em out! Only a flat black surface is a good surface.

Similarly you can go and remove the Barlow, shine a flash-light into the scope's front end and then look into the focuser: Do you see any reflections were they shouldn't be? Flock 'em!

And for ultimate satisfaction, put eyepiece(s) in the focuser, shine the flash-light from the front and then look from the front: Do you see any reflections? Remove 'em! All my eyepieces (and all my star diagonals) had chrome barrels were the front edge and the inside of the barrel reflected light like crazy. And even if the inside of the barrel was painted in flat black, it was not nearly enough. Especially in the case of the 2" star diagonal I had a huge improvement by flocking the barrel.

So, if it shines in the flashlight, it is bad for contrast. It is most obvious on objects like the Moon or the planets. In other cases (e.g. when there are bright stars a little bit out of the FOV for a dark nebula) the result may be a little less obvious (though probably worth a try as well). As one of the next objects I want to see is Jupiter, I will be needing my Barlows, and I will want every bit of contrast I can squeeze out of my scopes. So the cloudy skies tonight were a blessing.

And one last thing I found: My SR6mm eyepiece has a lot of shiny black plastic surfaces at an right angle to the optical axis – putting some flocking material on it improved contrast especial in when used in combination with a Barlow.

BTW: In many cases I do not stick the flocking material on. I simply leave the protective foil on, roll up the flocking material and put it on the inside of e.g. a barrel. One just needs to cut it to the exact inner diameter of the tube (first make it a bit to long, then cut off small slices until it is "just right"), then one can lay it there "flush" and it will have a little bit of tension that holds the material there.

On other surfaces I try to put it in there so the flocking material holds there "mechanically".

Only in stuborn cases (were the material will not hold "by itself") do I need to remove the protective foil and stick it on the surface (point in case: the inside of the plastic retaining ring).

Cheap Astronomy – Blast From The Eighties: 60 / 900 Refractor With EQ-2 Mount

I could not resist it, I had to buy another cheap scope… :-) The scope was incomplete, and I bought it mainly for the EQ-2 mount – but it might turn out to be a nice entry level scope.

Some data:

• Bresser Art. Nr. 45-1200 
• Labelled "Circle T" (which means it came from the Japanese Towa company)
• No indication in which country it was actually manufactured (Japan? Taiwan? China?)
• Achromatic doublet refractor (commonly referred to as "Fraunhofer-type")
• The nominal aperture is 60mm
• The nominal focal length is 900mm
• This comes out to a long focal ratio of f/15
• Silver OTA
• The eyepiece size is 0.965 inch
• Came with an EQ-2 mount
• 6x30 finderscope with cross-hairs
• Focuser has "dual action": Rack-and-pinion and "pirate scope" sliding drawtube
• Almost everything is made from metal

The scope seems to be very similar to what has been (during the same time) sold under the Tasco Meade brandname in the USA. As far as I can see it is very similar to the Meade model 291 refractor. As far as I can see the 291 were made by Towa as well, though I could be mistaken. The silver series was supposedly the "slightly better" one from Bresser back then.

The scope came with the OTA, an EQ-2 mount without tripod legs, one prism diagonal, one "Porro" erecting prism for terrestrial use, a 6x30 finderscope with bracket and all of the little screws and most of the caps (plus the packaging from a similar "Apollo" telescope). What was not included were eyepieces, nor were there any tripod-legs, the eyepiece tray or light for the tray (but the tripod legs from my EQ-1 fitted somewhat, so I borrowed them). Missing as well was the counterweight-rod and control cables for the EQ-2 mount (again, borrowed from my EQ-1), as well as one nut for closing the OTA-bracket.

Both the scope and the mount seemed like they have been seldom (if ever) used, though there was some wear on the finderscope and the prism diagonal. There is even still the protective foil on a scale of the mount and on the knobs of the focuser!

Granted, the aperture is small, but the focal length is long, so I should be able to try higher magnifications for planetary viewing on Saturn or Jupiter with my still limited selection of eyepieces.

And of course, when one buys a scope, the weather turns bad. So I made only some preliminary tests. The chromatic aberration seems very small, as should be expected from a f/15 focal ratio. During the daytime I could increase the magnification so far (with my cheap 3x Barlow) that I started to see dust on my Ortho10mm, and started to see some floaters and other crud in my eyes with my H6mm.

Some of the things I noticed:

• OTA outer diameter is 63mm
• The counterweight-rod for EQ-2 mount has probably an UNC 1/2"-13 thread, (unlike the M12 thread on my EQ-1)
• The counterweight-bar of the EQ-2 rotates with the scope (unlike the EQ-1)
• The tension of the "pirate scope" focuser is maintained by cardboard – obviously this cardboard has deteriorated over the years, and the focuser has lost tension. So I needed to take the focuser apart, put one carefully placed piece of electrical tape on the cardboard (not on the circumflex, but along the length of the cardboard) and reassemble it all. Now it is a bit too firm, but that is OK.
  [Update] I had to completely remove the cardboard from the drawtube, it was getting loose again and adding tape made it worse. I put three strips of "textile" tape in there, padded it with several layers of electric tape and topped it of with thin "aluminium tape" – now it seems good. And what's more, it is easy to add tension by adding layers of aluminium tape. [/Update]
• Little pieces of the cardboard (from inside the focuser) had found its way on the rear surface of the lens. And there were some defects in coating of the rear surface, probably caused by the rotting cardboard pieces. But after removing the dirt, the damage seems benign.    
• The finderscope seems OK.
• The finderscope's bracket is of "single ring" type, with three set-screws – and adjusting it is impossible without modification, as the end (opposite of the set-screws) is too wide for the finderscope. After I put a layer of electrical tape around the finderscope (opposite the set-screws) I could adjust the finderscope reasonably well (and when tightened down all screws a bit, the finderscope seems to stay in alignment – everything is metal, after all).
• The 60/900 is much lighter than my 76/700 Newton – the one counterweight I have (which is just about enough for the Newton) is too much for the 60/900!
• The OTA and focuser seem to be properly baffled. The baffles inside the focuser's drawtube are small, however both a rough estimate and a visual inspection confirm that the baffles are very well placed. (Only minor point is that both baffles inside the drawtube are not painted black, but instead have their "natural" metal brass?/galvanized? finish)
• [Update] The focuser had some shifting, and I when I dismantled it to remove the cardboard, I removed the single piece of textile tape that was put there in the focuser – focuser shifting is awful at an telescope and most of the time it would be completely avoidable during production with some simple measures. But one can make a simple DIY solution: Instead of the single piece of tape, I put two "rails" from flocking material in the focuser (as I did in the 70/300). That greatly reduced focuser shifting, but there is still some. I will have to improve the "rails" at least once more, but I'm confident that I can remove the shifting almost completed within two iterations. [/Update]

I'm going to play around with a bit, and ask a friend to make me make myself some simple wooden tripod-legs for it. And then I need to get another counterweight rod and something as counterweight.

It seems like a nice scope.

[Update 2013-08-14]
Today I tried solar projection using an Carl Zeiss Jena microscope-eyepiece (Huygens 35.7mm) and I must say this scope (with its small aperture, long focal ratio and metal baffles) is well suited for observation of sunspots. As long as we still have observable sunspots, that is.

An image made today (14th August 2013) by the SDO solar space observatory captured in the 4500Å continuum. The image shows the two medium sized sunspot groups (or rather several groups), which I could spot as well with my 60mm/900mm refractor by using eyepiece projection.

Cheap Astronomy – A Quick Look At The Bresser 76 / 350 Table-Top Dobson

A supermarket chain here has been selling off the "Bresser 76 mm (3 inch) f=350mm table-top Dobson telescope" at a very very low price. So naturally some of those sold wound up at eBay, with an surcharge (naturally), and naturally I had to buy one. (Had I known of this offer by the supermarket chain in the first place, I would have obviously bought directly there, saving myself a bit of money – but I digress, back to Cheap Astronomy).

The scope has arrived this morning, so I hadn't had a chance to test it on the night sky. I however played around a bit with it, and I thought I write down what I learned so far (and as I doubt I have the energy at the moment to do a proper review of it anyway). [Update] And of course the weather turned bad the afternoon… [/Update]

What's in the box:

• The table-top Dobsonian telescope (Art. No. 88-43201)
• Nominal aperture is 76 mm (3 inch)
• Nominal focal length is 350 mm (13.8 inch)
• The nominal focal ratio is f/4.6
• An H20mm Huygens(?) eyepiece (1.25 inch), giving a nominal 17.5x magnification
• An SR6mm Ramsden eyepiece (1.25 inch), giving 58x magnification
• An 2x "shorty" Barlow (1.25 inch), increasing the nominal magnification to 35x and 117x respectively
• And blue "Moon filter"
• Caps for focuser and Barlow, canisters for the eyepieces
• An planisphere
• An CD with the Stellarium software
• Some documentation
• A finderscope is not included

The telescope (and mount) features:

• An 1.25 inch focuser 
• A single-arm secondary mirror support
• The OTA has an outer diameter of about 95mm (the end caps are about 1mm larger in diameter)
• Two setting circles, one for azimuth and one for altitude
• The tension of the altitude axis can be adjusted with a large knob
• An wobbly compass in the base

A quick estimate regarding the secondary and effective aperture:
The secondary mirror has about 19mm diameter (small axis, +/- 1mm) and is about 235 mm (+/- 10mm) away from the main mirror.

If I did not make an mistake:
To illuminate an 20mm diameter field at the eyepiece, the secondary diameter would have to be about 40mm – for 5mm this comes out to about 29mm diameter. With an 19mm secondary, the on-axis aperture becomes around 60mm.

Taking into account the (arguably small) obstruction of the secondary with sqrt(60*60 - 19*19) sqrt(30*30-14.5*14.5)*2, we end up with about 57mm (2.25 inch) effective aperture. (For comparison a 29mm secondary would yield an effective aperture of about 70mm)

Blunders, big and small:

• The main mirror is probably spherical (will see how the stars look)
• The main mirror is not adjustable (adjustment on mine seems fine though)
• The secondary is (probably) too small
• [Update] After a short visual inspection I can confirm that the secondary is definitely too small.
• [Update] Furthermore the position of the secondary is not centred when viewed from the focuser (the secondary is moved too much towards the front). The collimation screws of the secondary are too short and make achieving a proper collimate impossible! One has to replace the screws with longer versions!
• [Update 2013-10-06] I replaced the secondary's screws with a bit longer versions – now I could put the secondary were it belongs. (And I need to buy some long M3 screws.) I collimated the secondary (no Cheshire, no laser) and I hope it should now be better – a daytime test was promising. Before collimation the image from the Pleiades was a bit disappointing compared with my 70/300 refractor – let's see what it does the next time at the nightsky after collimation.
• [Update 2013-10-07] With longer screws and after collimation the scope is much improved. Looking at the Pleiades the view is almost like that from my 70/300 refractor – the Pleiades were not a pretty sight before collimation in the little Dobson. Maybe with proper collimation tools (Cheshire and Laser) I could improve it a bit more beyond that – but this has to do.
• The focuser shifts quite a bit. 
• The eyepieces are not parfocal (which is aggravated by the focuser shifting)
• Using the eyepieces with/without the Barlow is not parfocal (again bad due to focuser shifting)
• The altitude setting circle has some +/- 5 degrees play with respect to the telescopes altitude (with 0 degree deviation from true altitude being on the end of the play!)
• The altitude setting circle furthermore is black on silver
• The altitude tension is very difficult to adjust
• The azimuth tension seems a bit to light (and is not easily adjustable)
• Already during the daytime the planisphere is impossible to read!!! Seriously, WTF???
• The mate black paint in the OTA is not fully dark. It seems however to be somewhat OK (and I refuse to flock anyway).
• There are no provisions to add an finder 

Other

• The H20mm eyepiece has its field stop before the field lens – this indicates that it is in fact not a Huygens type eyepiece. (The optics looks the same as those from the H20mm eyepiece supplied with my 70/300). Whether this eyepiece is a Ramsden or a Kellner eyepiece, I don't know.

What's nice:

• The focuser has enough travel (especially compared to my 76/700 Newton)
• The focuser position is located at an angle (some people like that, some people hate that…)
  
• The focuser retention ring can be (with some fiddling) exchanged with my 70/300 refractor, making it possible for me to use both 0.965" and 1.25" eyepieces – though this fiddling will be a bit hard under night-time observation conditions…
• The telescope vibrates when touched, but being so lightweight the vibrations die down completely within an second (give or take).
• The setting circles, are both quite large – during the daytime they helped me measuring out the local horizon at one observation site. Whether they are helpful during the night is doubtful though.
• The azimuth setting circle is printed white on black, which is good (though the font and scale used is a bit "thin", which is bad).
• The compass looks like a toy (and behaves like a toy compass), but it is a nice touch.

tl;dr

• Focuser shifting is awful. Fixing the shifting is difficult, as the space between drawtube and focuser is small – the "two rail" solution I employed at my 70/300 refractor is not easily possible here…
• The secondary mirror is too small (which is probably for the better, considering the probably spherical main mirror): The effective aperture is probably about 57mm (2.25 inch) according to my calculation (which might be wrong)
• The actual focal ratio therefore is probably closer to f/6.1
• But other than focuser shifting, the telescope seems usable to play around – though I have not tested it properly yet.

[Update 2013-08-17]
I shortly tested it on the Moon tonight. The phase was 45° (waxing gibbous) and the Moon was already very bright. I forgot to bring the "Moon filter" with me (nor any of the other filters I have) which was a big oversight – after the session my observation eye was in photopic vision. o.O

Both the H20mm (which is really a Ramsden or Kellner) and the SR6mm performed admirably when observing the Moon in this table-top Dobson. I brought my other 1.25" eyepieces with me (an PL10mm, an SPL12.5mm and an SPL25mm among others) and they too provided very nice views of the Moon.

I then tried the supplied 2x Barlow and the result was quite a bit visible "false color", blue and orange/purple fringes – regardless of which eyepiece. Furthermore the field seemed a bit tilted, which made focusing the entire field not really possible, plus the color seemed not the same on all edges. Possibly the Barlow's lens is tilted. So at least in this fast scope such an cheap supplied Barlow is not a good choice. However with an good Barlow on the Moon this scope should be able to provide more than 120x, or so I would guess. I have ordered (hopefully better) Barlows and I will see how they do in this scope.

This observation of the Moon was followed by a serendipitous naked eye observation of an ISS pass (As Tony Darnell says: "Keep looking up!"). It was quite a sight! But the ISS's magnitude of -3.2 was, with an waxing Moon, "only" comparable to one magnitude less without the Moon in the sky… Still, it was very nice.
[/Update 2013-08-17]

[Update 2013-08-20]
I took a good look at the Barlow and found that the retaining ring (coarse plastic thread) was threaded in tilted. I removed the retaining ring, removed the white goo from the lens (what seems to be a singlet(!) lens, but at least a glass lens), blackened the edge of the lens and put it all carefully together again. Then I made another threaded hole for the retaining screw, as the original was slightly angled in such a way that it pushed out an eyepiece if you tightened it down.

Then tonight I made a short test at the Moon. This time I had my filters with me. I tried them all. The supplied blue "Moon Filter" has a nice color, but is not nearly dark enough. Of all my other filters only the "B+W #103 8x" (optical density 0.9, adds 3 stops) brought down the light level enough, and just barely at that. A combination of filters would have been interesting, but the reflections on two adjacent filters meant a stark degradation of the image – so only the ND filter.

First of all: the "strange color" which I saw is only visible in the supplied H20mm – whatever it is, it seems to be a problem of the eyepiece design. Otherwise the H20mm eyepiece seems sharp. Will see how it does with longer a focal length telescope.

I again tried the Barlow with my H20mm, PL10mm and SR6mm eyepieces (as the other eyepieces have no threads for filters). It was not possible to focus the combination of SR6mm and 2x Barlow – there were always weird halos and everything was washy. Both the PL10mm and the H20mm gave an somewhat sharp image, but it was discernibly worse than without Barlow – not but a large margin, but noticeably.

So as expected the Barlow is not something one should pay money for.

And while the focuser shifting is somewhat reduced with the "two rail" measure I took, it is still awful.
[/Update 2013-08-20]

[Update 2013-08-24]
After fixing one last problem, I can say that the Barlow is not so bad after all!

I found one more spot in the Barlow were there was a black shiny plastic surface causing an internal reflection: The inside of the lens' retaining ring! Small, but vicious. After I put a little strip of black flocking material on the inside of the retain ring I was rewarded with an hugely improved contrast! All my eyepieces now produce a (almost) sharp image. It is not "tack sharp", but it is not so bad compared with my other (more expensive, and better) Barlows.

It is of critical importance to track down and remove all sources of internal reflections! This is especially important in fast scopes, as their divergent light path is much more susceptible to cause internal reflections.
[/Update 2013-08-24]

Cheap Astronomy – DIY Tools And Materials

When doing Cheap Astronomy, one needs to modify cheaply bought astronomical equipment – there is no way round. So one needs tools and materials to fix all the shortcomings. Inspired by this Tested.com's podcast and their very excellent list, I thought I put together my own list.

Most of the stuff is not specific to DIY Cheap Astronomy, but instead can be used for other DIY projects you might want to make.

Missing is an extensive material section – like plastic piping, aluminium profiles, wood, and so on. For such material, go to your local hardware stores and see what they have. Especially wood is easy to work with and I can recommend trying out doing some things in wood. I hope I will add a post about materials in the future.

Also missing is an electronics section (soldering iron, wires) – that would be another post for itself.

First of all: you do not need all of this.
You have what you have, so don't buy stuff (unless you absolutely have to) and instead try to do things with what you already have.

But if you see one or the other thing from this list for an affordable price, then by all means get them. In some things I would maybe invest a little bit more (e.g. a good ratchet wrench with sockets), other things I buy as cheap as I can get (e.g. a metal hammer or a set of metal files).

Then when you need a saw, you can get by with only one metal saw – you don't need a hand saw and a jigjaw and a circular saw and an angle grinder. The same goes for hammers – one metal hammer should get you going.

BTW: The versions for working with metal (e.g. metal drill bits or metal saws) are usually fine for working with plastic or wood.

Work area:
What I found helpful is having two working surfaces: One wood bench for "dirty" work (e.g. drilling, grinding) that can be in the basement, garage or somesuch – or even outside! A small bench can suffice for this. And the other work area is then one table for "clean" work, which can be your normal "office" desk or even a kitchen table.

If you have only one work area, then put your vacuum cleaner nearby whatever you do (e.g. grinding, drilling), tape down the hose if necessary and suck away all the dust and slivers before they settle on every nearby surface. But be careful not to use your vacuum cleaner for hot stuff (e.g. when grinding or drilling metal with high speeds)!

Staying organized:

• Get sorting boxes! And get as many as you can afford. Usually quite expensive, so look around and if you see cheap sorting boxes, then get them!
• Drawer units are highly recommendable. Look around for what size(s) suit your needs best.
• Find a place for every bit, where you can easily get things, and can easily put them away again. E.g. keep the drill stand in the shelf, the drill bits in the top drawer, the files and hammers in the drawer below, the ratchet wrench below that, and so on.

Occupational safety and health:

• Get safety goggles to protect your eyes while using powertools. Get some goggles with good ventilation, and maybe some from the "anti-fog" variety.
• Get earplugs or acoustic earmuffs to protect your hearing while using powertools.
• Get a small fire extinguisher for every room you work with powertools like drills or grinders.

Dark out for astronomy:

• Matte black paint
• Black flocking material

Getting things right:

• Tape measure
• Calipers
• Steal ruler

Tools for screwing around:

• A set of metric combination wrenches (or open-ended wrenches): With at least sizes 7mm, 10mm, 13mm and 17mm.
• A 1/4" ratchet wrench and metric sockets: You need the sizes from above, plus possibly other sizes.
• A set of slot/cross screwdrivers or bits (or both): Usually Phillips #1/#2, Pozidriv #1/#2, flat head #1/#2, maybe smaller/larger sizes as well.
• A set of allen wrenches or bits (or both) for metric hex keys: You possibly need all sizes from small to large (2mm, 2.5mm, 3mm, 3.5mm, 4mm, 5mm, 5.5mm, 6mm, 7mm, 8mm and 10mm)
• Maybe some hexalobular socket ("Torx") tools as well
• A good pop-riveter with rivets is nice. (Get one that can handle M3/M4/M5/M6 threaded rivets!)

Bolts and nuts:

• Metric M3, M4, M5, M6 and possibly M8: Bolts, nuts, flat washers, star washers, threaded rods and other such things.

It is difficult to say what you will need, and how many. At first, buy only what you need, and maybe a little bit more than you need. E.g. if you need four M4 nuts, then buy maybe six or eight – but if you can spend a little bit on top of that and get a set of say 20 M4 bolts and 20 M4 nuts, then get it! If you continue working like this then over time you will build up a collection of bolts and nuts. And by that time you usually get a feeling for what you need.

Tools for drilling, cutting, grinding and hammering:

• A drill
• A matching drill stand is helpful (to create a small drill press)
• A "small" machine vise
• A bench vise can be helpful
• Utility knives (e.g. "X-Acto")
• A set of metal files (I find that I need these four: normal sized hand file, normal sized half-round file, small&fine hand file, and small&fine half-round file)
• Metal hammer (small and large)
• Possibly a plastic mallet
• Some metal saws
• A jigsaw with blades for metal
• A angle grinder can be helpful (a small one with an thin disc will suffice). 
• If you combine the angle grinder with a stand for cutting, then this will create a simple chopsaw.
• A proper electric hacksaw/chopsaw (like the one pictured here and here and here) is helpful if you want to cut down the tubes of OTA (and want to make sure to cut at an right angle).

Bits and pieces:

• Metric metal drill bits: I once bought a set of (cheap) drills from 1.0mm to 6.0mm in 1/10 mm increments – this is pure heaven. But what you have is OK (you can even get far with drill bits in imperial sizes).
• Metric threading tools: A tap wrench with a set of metric taps (M3, M4, M5, M6 and M8 should suffice, but you will need some matching 2.5mm, 3.3mm, 4.2mm 5mm and 6.8mm metal drill bits as well!). And maybe a die wrench and M3 to M8 dies as well (usually comes in a tap&die set anyway).
• Imperial threading tools: A 1/4"-20 UNC tap and a 3/8"-16 UNC tap can be helpful (the two sizes used for photo-tripods, cameras and so on).

Chemicals:

• A little bit petrol or diesel fuel: E.g. for getting rid of grease (like in mounts).
• Maybe an dedicated degreaser.
• Paint thinner: Good for cleaning and preparing things you want to paint.
• Some grease: Preferably non-sticky and non-runny, like e.g. lithium grease. But Vaseline or any other brand of petroleum jelly will usually do fine as grease.
• Alcohol, specifically pure isopropyl alcohol: For cleaning optics
• Orange oil based solvent: E.g. for removing residues from sticky tapes or adhesive label.

Some of these things are bad for health and environment: Store the stuff safely. Keep the room ventilated where you use that stuff and avoid extended exposure. Use only what you need, don't waste it, and don't put it in the sewer or in the ground.

Sticky business (glue, tape):

• Electrical tape
• Duct tape
• Doublestick tape
• Foam doublestick tape
• A fast 2-component glue (e.g. 5 minutes / 20 minutes) is helpful.
• A slow but hard 2-component glue is helpful.
• Contact cement is helpful.
• Hot glue (with matching pistol) can be helpful
• Cyanoacrylate (e.g. "Super Glue") can be helpful. But keep this stuff as far away from optics as you can! It will deposit a ugly and hard residue on any nearby surfaces.
• Maybe get some thread-locking fluid as well.

Learn to use each glue properly, and learn what is the right glue for the right job – it really pays off.

This will have to suffice for now. I am sure I have forgotten some things, but I will add them later, I swear!

What Is Cheap Astronomy?

I think I owe (the few readers who stumble here by accident) an definition of what I consider "Cheap Astronomy":

For me, Cheap Astronomy is not about getting the cheapest astronomical gear, nor the worst! (So it is not "Bad Astronomy"). But instead it is for me trying to maximise the astronomy one can do "on the cheap", it is astronomy with an limited budget.

And as I am new to astronomy, I will try to write from the perspective of a newbie (who has some limited experience with optical gear).

Cheap Astronomy – Using Microscope Eyepieces For Astronomy

An important part of astronomy is having a selection of eyepieces at one's disposal, as it is important to e.g. lower the magnification to locate an object, increase magnification to see details of an object (e.g. an planet), or generally adjust the properties of the optical system due to various parameters (size and brightness of object, aperture and focal length of the telescope, desired exit pupil, and so on) to optimize the astronomical observation of an object.

One can spend a lot of money on eyepieces, as even cheap (but reasonably good) eyepieces, that cost next to nothing in production – like simple Plössls, that are thrown in for free with various entry-level telescope sets – are rather expensive if one buys them alone. Buying a scope with included good eyepieces is a good start, but it only gets you so far – so having microscopy as another source of (usually) cheap eyepieces is good.

A short interlude:

If I write here about microscopes, I mean "monocular" microscopes, and not stereo-microscopes – the later are a different beast, and AFAIK not such a good source of cheap eyepieces. (And just in case: a monocular microscope with an binoviewer is not an stereo-microscope.)

Mechanical and labeling differences

But of course, while there are a lot of similarities between eyepieces for microscopes and for astronomy, there are unavoidable differences. The first difference between an eyepiece for an telescope and one for an microscope is the outer diameter of the eyepiece barrel. There are three established sizes for astronomical eyepieces:

• 0.965 inch (24.5mm)
• 1.25 inch (31.75mm), aka "1 1/4 inch"
• 2.0 inch (50.8mm)

The 0.965" size was common long ago for (smaller) Japanese telescopes, and is found today mainly on cheap telescopes. The 2" size is typically found on the larger and on the more expensive telescopes, which leaves the 1.25" eyepiece size as the semi-standard for entry-level and for some of the compact telescopes.

On the other hand, the majority of microscope eyepieces come in the standard 23.2mm size. More modern sizes for microscope eyepieces include the 30mm (and 34mm) standard, while some manufactures use even other sizes. Buyer beware. Typically older microscopes come with 23.2mm eyepieces, while 30mm would be found rather with newer microscopes (but some new microscopes still come with the old 23.2mm standard).

Another interlude:
Don't buy toy microscopes

It has to be said: There are many different microscopes that one can buy (research, medical, metallurgic, or student microscopes, to name a few), and then there are these obnoxious toy "microscopes" (with little plastic "boxes" and some toy-gadgets like toy-tweezers, and prepared glass slides). Typically a proper microscope is heavy (easily a kilogram or two), and typically the distance between microscope lens and microscope eyepiece is about 160mm, some 6 inch (with larger specimens going into the tens of kilograms and requiring an table of its own). As a "rule": anything that is substantially lighter or smaller is typically a toy, giving you only an hint of what an "real" microscope could do – so do not buy toy microscopes. (There are exceptions to this "rule": good small microscopes for mobile use – but these tend to be expensive.)

Furthermore, while it is tempting to buy such a toy for cheap and take it apart (which can be instructive in itself), it will however not help you get useful eyepieces for astronomical use out of it, as the eyepieces in these toys are typically not suited for astronomy at all.

So back to proper optical gear…

A 23.2mm microscope eyepiece can be usually fitted in any piece of astronomical equipment that accepts 0.965" inch (24.5mm) eyepieces. While one can simply mount an 23.2mm eyepiece in an 0.965" telescope (if the screw to hold the eyepiece is long enough) and ignore that the eyepiece is slightly offset from the axis, it is advisable to pad the diameter. I have made good experiences with adding four layers of electrical tape to my 23.2 eyepieces, which works fine for me (so far) – and the tape can be removed if necessary.

Usually the mechanical stop on the microscope eyepiece is larger than 24.5mm and will hinder the eyepiece from taking a plunge into a 0.965" scope, but check this first – before you drop your eyepiece inside the telescope…

Same as above, 30mm microscope eyepieces can be used instead of 1.25" eyepieces. (But as the selection, quality, price and suitability for astronomy of 1.25" astronomical eyepieces is usually better than that of 30mm microscope eyepieces, I find it not so interesting – but do try it if you have a chance!)

On a side note, there seem to have been telescopes which would accept directly 23.2mm microscope eyepieces – but such instruments are rather rare, and therefore don't really matter for Cheap Astronomy.

Microscope eyepieces are labelled in "magnification power" (e.g. "15x"), which is a measure by how much the focal image of the microscope is magnified. You can calculate the focal length from this formula:

focal length (in mm) = 250 / magnification power

Or the other way round:

magnification power = 250 / focal length (in mm)

And here, for your benefit, is a focal length conversion table for some common eyepiece magnification powers:

Eyepiece magnification power	Focal length
4x	62.5 mm
5x	50.0 mm
6x	41.6 mm
7x	35.7 mm
8x	31.3 mm
10x	25.0 mm
12x	20.8 mm
15x	16.7 mm
16x	15.6 mm
20x	12.5 mm
25x	10.0 mm

Other microscope accessories

One interesting variant of microscope eyepieces are "projective eyepieces" (or "Projektiv" in German). These are specially designed for what is called "eyepiece projection" in astronomy, where the image is directly projected to a camera (directly onto film, and nowadays directly onto a CCD or CMOS camera sensor) without any further optics. The magnification of such an "Projektiv" is expressed as a ratio (e.g. "3,2:1" or "4:1"). I haven't tried these myself, but suspect that such eyepieces might be interesting for astrophotography. (There a "K" type or "Kompensationsokular" versions out there, which are probably not suited for astrophotography – but I may be wrong.)

Another interesting type of microscope accessories in 23.2mm are binoviewers. Though due to their weight possibly a bit more difficult to adapt to an telescope, these might be interesting for astronomical use. However such binoviewers are more susceptible to dirt, miscollimation and general mistreatment, and are a bit more delicate than eyepieces. Either you have to pay more for one with guaranteed quality. Or if you get a cheap one with unknown quality, then be prepared to sell it again if isn't up to spec (and it is too difficult for your set of skills to clean and align it). Of course you can use an microscope binoviewer only with microscope eyepieces (unless you mechanically modify the binoviewer), and you now need two of each microscope eyepiece you want to use in it.

As to microscope Barlows, I'm afraid I haven't seen any such device in the wild… They are rumoured to exists, but are probably the domain of microscope aficionados, and not Cheap Astronomers. Some microscopes have an build-in zoom capability (or you can add a tube for zooming), but these tend to be rather heavy instruments – nothing I would mount to any of my cheap scopes.

Some notes on microscope eyepiece for astronomy

Using microscope eyepieces for astronomy has several drawbacks and there are some things you should keep in mind:

• The 23.2mm size limits the possible FOV.
• 23.2mm is slightly smaller than the 24.5mm of the 0.965" size, and padding the diameter is recommended (e.g. electrical tape works fine for me).
• You can't easily mount 1.25" astronomy filters.
• Microscope eyepieces can usually be quite easily fitted with reticles. Though the reticles are not illuminated, the reticles available are more interesting for microscopy than for astronomy, and the sizes of the reticles differ quite a bit between different makers (and even different models!)
• Low-power eyepieces are typically of a simple type type like Huygens, Ramsden or Kellner. While microscope Huygens eyepieces are superior to the Huygens eyepieces supplied with cheap scopes, they still offer the same small FOV.
• Anything shorter than 42mm (or "6x") is rare, with the occasional "5x" or "4x" being advertised. As the FOV is restricted to 23.2mm, these low-power eyepieces don't make too much sense anyway.
• High-power eyepieces (focal length shorter than 17mm or "15x") are difficult to come by, the highest power I have seen was my 10mm (or "25x"). This is due to the fact that one can easily change lenses on an microscope (and has typically a selection of different powered lenses mounted in an turret) – unlike the typical astronomical telescope, where one changes only eyepieces instead.
• Microscope eyepieces have typically lenses/elements that are not coated (but have typically less lenses/elements anyway).
• Microscope eyepiece have typically more internal reflections than astronomical eyepieces (which can be alleviated somewhat with flocking and somesuch DIY measures).
• For microscopy Kellner eyepieces are considered "wide field" (WF)
• Some combinations of microscope eyepiece and astronomical telescope can have excessive field curvature. Then you will have a sharp image "on axis" (in the middle), but out of focus image on the edge (and vice versa).
• Some microscope eyepieces are special types, which are usually marked (e.g. "KPL" or "CPL") – with typically P ("phase contrast"), C ("corrected" "compensating eyepiece") or K ("korrigiert" "Kompensationsokular"). These are made for special microscope lenses (to compensate an undercorrected color aberration of some microscope lenses), and will not work properly in astronomical telescopes. Every manufacturer uses its own codes (and the LOMO "C15x" is not an "compensating" type, but an symmetrical type, from the Russian/Cyrillic "симметричный"). And moreover some speciality eyepiece are not properly marked!
• Bottom line: some microscope eyepieces work nicely in telescopes, some less so. Some work better in telescope A than in telescope B. You have to try them out.

My experience

It is my personal experience with microscope eyepieces (in my two telescopes) that the Huygens eyepieces from microscopes (one CZJ, the other possibly from PZO) are far superior to the Huygens eyepieces supplied with cheap telescopes – but they are still Huygens eyepieces, with small FOV. So if today I had to choose (at comparable price and focal length) between an simple&cheap microscope Huygens, and an simple&cheap astronomical Plössl, I would take the Plössl (and after all, decent Plössls are not that expensive if you look around). And the same is true for the better microscope eyepieces I have (like the 17mm symmetrical, or the 10mm ortho): If you have to choose (at equal price) between an 10mm microscope Abbe ortho, and an similar astronomical Abbe ortho, then take the astronomical version.

When on the other hand you start out with astronomy (and have maybe a scope which accepts 0.965" eyepieces), and can get microscope eyepieces cheaper than comparable astronomical eyepieces (e.g. three microscope eyepieces for the price of one astronomical eyepieces), it can make sense for the Cheap Astronomer™ to get some microscope eyepieces instead. And if you already have an microscope with some eyepieces anyway (or plan to get one), than I would highly recommend to any self-selected Cheap Astronomer™ to give microscope eyepieces a try on the night sky.

BTW, I got my microscope eyepieces through two routes: I bought an old Carl Zeiss Jena (CZJ) "horseshoe" microscope, which came with several eyepieces. And then I bought microscope eyepieces (like the 10mm Abbe ortho and the 17mm symmetrical) when I had the chance.

Buying a microscope that comes with several eyepieces is a nice way to increase one's eyepieces collection. The included eyepieces are typically of simple type (Huygens, Kellner) and of lower power (maybe 40mm to 17mm, sometimes 12.5mm), and make nice "overview" eyepieces. If you have bought an microscope with eyepieces, you can either keep the microscope – most of them are fine instruments which can be handy sometimes – and use the eyepieces for both astronomy and microscopy. Or you go (after you have tested all eyepieces with your telescope and determined which ones to keep) and sell the microscope again with only one or two eyepieces (keeping the useful eyepieces) – and usually you still get an reasonable price.

What I found recommendable and affordable are the microscopes from former communist production – companies like Carl Zeiss Jena (CZJ), LOMO, PZO or Meopta. One advantage is that the eyepieces from communist production are typically not of the "corrected" type (or only very slightly corrected) and will work nicely in astronomical telescopes.

Furthermore, affordable scopes are/were sold by Bresser (like the Biolam – which used to be from LOMO production, if I am not mistaken, but now is supposedly from the Far-East). And of course the Chinese (and other Asian nations) are increasingly getting better at producing goods like microscopes (but older ones can be quite awful).

And if you can get an affordable used microscope from "western" production – from companies like Zeiss Germany, Leitz, Olympus, American Optical or Bausch&Lomb – then by all means try them (though at least Zeiss Germany has an tendency to supply "corrected" eyepieces).

And don't pay too much for an microscope! 20€ to 30€ is a good price here for a simple microscope (e.g. an "horseshoe") with three or four eyepieces (and three or four microscope lenses), with 50€ being way too excessive. And this is Cheap Astronomy after all, where we stay cheap, even if we stray into other optical realms.

tl;dr

In conclusion it might make sense for an Cheap Astronomer to get one or two simple Huygens microscope eyepieces in the area between "4x" and "7x" (something between f=63mm and f=37mm). Furthermore the mass-produced LOMO "C15x" (f=17mm) is not that expensive and an really nice eyepiece (an "symmetrical" eyepiece, which is a simple version of an Plössl) – I love using it. Maybe an "20x" microscope Kellner "WF" eyepiece would be a good addition for astronomy. And finally if you can get an high-powered microscope eyepiece (like the "25x" Abbe ortho 10mm I have) for an low price (lower than an comparable astronomy eyepiece!), you should consider buying it.

If you have a telescope that accepts 0.965" eyepieces and you have some 23.2mm microscope eyepieces (or can get some cheaply) then by all means do try them in your telescope! The same goes for 30mm eyepieces in 1.25" scopes.

Furthermore you will need to test the eyepiece with your telescope – some microscope eyepieces work better than others – depending on both what eyepiece and what telescope.

Don't pay more for microscope eyepieces than you would for comparable astronomy eyepiece – microscope eyepieces make only sense when you can get them cheaper than astronomical ones (e.g. as bundle, or together with an microscope). Or of course when you want to actually use them for microscopy. Don't shop around for expensive microscope eyepieces if you want to use them exclusively for astronomy – then rather get good astronomical eyepieces instead.

Microscope "projective eyepieces" (or in German so called "Projektiv" eyepieces) might make an nice addition for Cheap Astrophotography when you do eyepiece projection – though I have no experience with this.

Microscope binoviewers might be a cheap route if you want to add binoviewing to you Cheap Astronomy inventory.

Cheap Astronomy – Review (And Improvements) Of The "Astronomical Telescope Model 30070"

[Update 2013-08-23]

The 70/300 refractor I bought is stopped down to an aperture of about 30mm (!) due to various points:

• Small focuser (0.965")
• Baffle in the focuser's drawtube
• Small star diagonal (again 0.965")

The worst offender is the baffle in the focuser's drawtube, and by removing it you can increase the effective aperture to about 50mm (which is still bad).

Due to the fast focal ratio, the only way to get the full 70mm aperture is to make some serious DIY modifications of this scope: One needs to add a larger focuser (the inner diameter of drawtube must be substantially larger than 1.25", depending on its length) and a larger star diagonal (at least 1.25").

Yesterday I provisionally adapted a 2" star diagonal and tested the scope with the full aperture of 70mm for the first time. The image of the (not quite) full Moon seemed fine. Chromatic aberration was present, but not so much as I feared (and the collimation was very coarse). The contrast of the Moon's mare was better than my 76/300 table-top Dobsonian – and that with a very coarse collimation of the 70/300. This is definitely promising for a first DIY ATM project.

But the problem is that the dimensions get problematic, as the 2" diagonal adds to much optical path, I now have little bit more of an centimetre (maybe half an inch) of distance between the end of the OTA and the flange of the diagonal. With the current length of the OTA there is definitely no room for an 2" focuser. Therefore I'm thinking about shortening (the already short) OTA…

Furthermore the 2" diagonal may be lightweight for its size, but none the less it has its weight and with the adapter to 1.25" eyepieces the scope is now quite back-heavy – one needs to move the attachment point for the tripod much further back…

An alternative would be to use an 1.25" diagonal. But frankly, if do such an modification, then I want to retain the possibility of using 2" wide-field eyepieces. Furthermore the position of an 1.25" diagonal can become critical: one should carefully measure the focus position for all the eyepieces (in combination with all the Barlows!) one owns to make sure if using a "small" 1.25" diagonal makes sense. For me, this is too much work, with too little benefit, and too much possibility of things one working out – so I will stick to the initial plan of using a 2" diagonal.

(And I now fully understand why the ETX60/ETX70/ETX80 are designed they way they are. Meade has put much thought into these scopes, and if I had the money and would ignore my GOTO allergy, I would probably get all three of them, plus probably the ETX90, ETX105 and ETX125… Or maybe if I had money I would get the OTAs and put them on proper EQ mounts… One can dream.)

tl;dr
Scope is stopped down to about 30mm, and therefore "out of the box" unusable for astronomy. Though the scope makes a nice basis for an ATM project to add a larger focuser and diagonal – if you have some skills and can invest the time (and materials), that is.

[/Update 2013-08-23]

[Update 2013-10-11]

Success! With some DIY measures I finally managed to turn this alleged scope into an halfway useful wide-field scope! See update below!

[/Update 2013-10-11]


So this will be the first instalment of my "Cheap Astronomy" series, in which I will follow my aim to gaze at the night sky with as little investment as possible. I was inspired a bit by Steve Waldee's work (see here his excellent "consumer report" on a Skywatcher 70mm/700mm refractor), and I will try to do one or the other thing he does so well. Only on a much lower level, with much less experience, and by spending as little as possible. I will not promise that I write often – I'll have to see how much energy I can muster.

If you are mainly interested in telescopes that will put your neighbours to shame, then you are likely wrong here – if on the other hand you want to explore the wonders of the night sky at an budget (and enjoy doing some DIY improvements), then you came to the right place.

Here today I will try to write a review of the 70mm/300mm refractor telescope (or what passes for a "review" here at Cheap Astronomy HQ), a scope that seems to be ubiquitous with its colorful box (at least ubiquitous in my neck of the woods). Furthermore I will write down what I did to improve it.

To the stars clouds!
Ah, doesn't the scope look nice?
(Manfrotto/Bogen tripod, head and quick-release plate not included)

I have seen these scopes come up on eBay for quite some time now, but I haven't been able to find reviews of this 70/300 refractor scope – no forum posting, no blog posting, no nothing – could it be that there are none out there on the net? So this piqued my interest and I thought I attempt to get this little scope cheaply, to try it out myself.

Left: The edge of the FOV of my (cheap, cheap) 7x60 binocular

Right: The edge of the FOV of my "Model 30070" telescope (at 7x magnification, with supplied star diagonal and my H42mm eyepiece)

(Both images are to the same scale)

After my (cheap, cheap) 7x60 binoculars (ruby-coated!) turned out to have quite a bit of chromatic aberration, I fully expected this "Model 30070" telescope to manifests itself to be an horrible Chinese mess, with horrible coma, and horrible chromatic aberration and halos – in which case I would have sold it again. And out of the box it turned out to be useless for astronomy, however – given my (low?) standards – with some modifications the optics do actually perform very nicely, both during daytime and on the night sky.

So for me, this scope is a definitively an keeper.

Contents Of This Review Caveats What's In The Box (&Data) Showstoppers And Other Annoyances (+Some Fixes) Saturn An Waning Crescent (&Terrestrial Use) What's Nice & Pleasant About This Scope Under The Hood (&Measurements) What Remains To Be Done tl;dr

Caveats

(Back to table of content)

While I know a thing or two about optics, I am however new to astronomy. My foray into astronomy consisted of some (laughably little) naked eye astronomy over the past year. So when I write that something is bad, it usually is – but when I write that something is nice (or somesuch), that means it offers nice views compared to what I had before – which was that little naked-eye astronomy (and awful 7x60 binoculars). Seeing for the first time with "my own eyes" that the "little bright dot" we call Saturn has actually rings, that makes me truly blissful – even if I can't see Cassini's Division. So YMMV. Furthermore, your interests and needs may differ from mine, and what works for me might not work for you (and vice versa).

Secondly, what you get when you buy a "Model 30070" may differ from what I got – some things may change (without notice) for the better, some things may change for the worse.

Another caveat is that I used 2 decisively non-cheap pieces of equipment:

• A Manfrotto/Bogen tripod with ball-type head
• An Spindler&Hoyer 10mm Abbe orthoscopic microscope eyepiece

Each of which did cost me more than my binoculars, my two telescopes, all my other eyepieces and the (used) EQ1-mount combined. So it is a bit of a cheat to call this "cheap" astronomy, but I had them lying around anyway and decided to put them to good use (if only to have a reference).

The moderately expensive Manfrotto/Bogen 055PRO photo-tripod with ball-type head offers a surprising stable view for astronomical use (at 50x magnification with the "30070"), even with the central column fully extended – any vibrations die down very quickly.
The ball-type head is – while adequate for this scope – not really ideal for astronomy.

What's In The Box (&Data)

(Back to table of content)

I was lucky to pick up this telescope "used" for 10€ on the 29th June. The previous owner has only used it once and then sold it as a "scope for children". Typical prices here range from 20€ to 30€ (both used and new), but can go up to 100€ for new ones (which seems insane – but a capitalist has to do, what a capitalist has to do, right?).

So what did I get for 10€?

The colorful box, and what I found inside…

Mine came with:

• The Optical tube assembly (OTA), with an lens of D=70mm aperture and nominal f=300mm focal length (f/4.3)
• One standard 1/4"-20 thread on the OTA, to mount the OTA to an tripod
• An focuser attached to the OTA (BTW, all the eyepieces, the focuser, the star diagonal, the Barlow and the "erecting eyepiece" have an diameter of 0.965" / 24.5mm)
• Two eyepieces: One Huygens 20mm (H20mm) and one Huygens 6mm (H6mm)
• An (cheap) 3x Barlow
• An 1.5x image erection "eyepiece", for terrestrial viewing
• A 90° star diagonal
• An dew shield (which slides over the plastic "lens cell" of OTA)
• An two-part lens cap (which fits on the dew shield) – the two-part lens cap allows the scope to be stopped down to 41mm aperture
• An finderscope (5x10?) with cross-hairs and an simple bracket
• An simple tabletop tripod (the legs do not extend)
• Several 0.965" plugs for the various pieces
• Two eyepiece canisters

Sure feels like a "real" telescope, doesn't it?

The nominal data of the "Model 30070 Telescope"
And yes, the lens actually is coated (if only very slightly)

So here some the stats of this scope:

Astronomical Telescope 30070
Aperture	D=70mm (2.75 inch)
Focal length (nominal)	f=300mm (11.8 inch)
Focal ratio	f/4.3
Focuser	Rack-and-Pinion
Barrel diameter: Eyepieces Focuser Star diagonal Barlow	0.965 inch (24.5mm)
Magnifications for astronomical use with supplied accessories	15x with H20mm 45x with H20mm and 3x Barlow 50x with H6mm 150x with H6mm and 3x Barlow (last combo for Moon only – maybe)
Finderscope	5x24 (5x24 according to some websites, in reality it is out-of-the-box closer to 5x10)

Showstoppers And Other Annoyances – (&Some Fixes)

(Back to table of content)

Notice 1: For me, some things were fine with my scope, some things were horrible. If you buy one yourself, you may find a different set of problems that are horrible for you, and different things that might be fine for you.

Notice 2: Breaking things seems to much easier to achieve than fixing things (and sometimes the required skills for an task exceed the available skills). If you foolishly try to do what I did, and as an result break your telescope, then it is your fault – not mine.

So only try the following if you know the possible consequences – and in the knowledge that if things go south, that you might have to write off your money and your telescope. M'kay?

So, what's wrong with this scope?

I would say for astronomical use the main problems with the scope I got were as follows:

• The high-power H6mm eyepiece is of low optical quality
• The 3x Barlow is of low optical quality
• The focuser was loose (SRSLY?)
• The focuser only accepts 0.965" eyepieces and accessories, making upgrading difficult
• Internal reflections (lots of places)
• Useless finderscope, useless bracket for finderscope
• The base of the OTA (which connects to the tripod via a 1/4"-20 screw) does flex when you apply a little bit of force (e.g. when focusing). This leads to a problem that I mistook for "focuser shifting", but which isn't the fault of the focuser. (The focuser is, with some modifications, now fine and free of shifting as far as I can see.)

 I added two stripes of flocking material (that act kind of like "rails" now) to the focuser to fix the wobble – now it seems to work fine.

Some of the minor annoyances and lesser quibbles are:

• The lens cell is made from plastic and not adjustable (what did you expect from such an reasonably priced instrument?) 
• The lens edge is not blackened, and the lens cell is shiny black plastic
• The two eyepieces are not parfocal. If I exchange the H20mm for the H6mm (and vice versa), then I have to refocus.
• The finderscope has no protective caps. Everything else, gets their little caps and plugs and canisters, so you can protect them when you don't need them – but not the finder scope. Should this tell you what the makers thought about their finderscope?
• I can not put a eyepiece directly into the focuser, because I can't rack out the focuser out enough. You have to use either the star diagonal, the 3x Barlow or the "1.5x erecting eyepiece" to be able to reach focus. (On the other hand this is helpful if you want make astrophotography with focal projection – if the camera is lightweight enough for the focuser, that is.) There is one crude workaround for microscope eyepieces with 23.2 mm diameter: dismantle the "1.5x erecting eyepiece", use the front tube and slide the microscope eyepiece in. The eyepiece will sit there very loosely (and can easily fall out unless you do some more fiddling…), but you can use that tube as an spacer.
• When mounting the scope to a Manfrotto/Bogen quick-release plate, there is a piece from the "1/4 inch mounting base" of telescope in the way – one has to mount the plate the "wrong way round" (with the "lens arrow" on the plate facing the wrong direction).
• The "1/4 inch mounting base" is fitted with two screws to the OTA – one after the OTA's baffle, one before it. If you want to remove this mounting base (e.g. because you want to fit mounting rings) then you probably must remove the lens from the lens cell.
• I didn't bother to test the supplied tripod, as it is so short that you need to put it on a table to use the scope – and that was not possible from my observation site. (If you fancy such stuff, then you could use it as well like a sniper, if you lie down on the ground – but for astronomy this is useless.)
  [Update] Well, I did give the tripod a try during the daytime and it was as expected very disappointing. The 1/4"-20 screw is wobbly (is that the reason for the annoying protuberance on the scope's base and the complimentary "set-screw" on the head?). At 26.5x magnification the tripod is not nearly stable enough for this lightweight scope – the whole shebang shakes and wobbles like a leaf after the slightest provocation. Pointing the thing with its alt-az head is formidably horrible – it was easier to pick up the scope with its tripod than to pan with the tripod head. Not even usable during the daytime – what a waste of material and energy this tripod is.

We Can Rebuild It. We Have The Technology.

Cutting for better contrast!

To improve the scope I did the following:

• Removed the worst internal reflections (lots of places)
• Fixed the loose focuser tube (somewhat)
• Rasped/filed off a screw's burr, belonging to the focuser's eyepiece retaining ring
• Cursed at the useless finderscope and its equally useless bracket, after fiddling unfruitfully with it for quite some time

Getting rid of reflections

When testing the scope during the daytime I had some instances where contrast was really bad, which I could track down to internal reflections. The worst combo was using the 3x Barlow together with the star diagonal and looking in the general direction of the daytime sky.

To get rid of internal reflections I did the following:

• Applied flocking material for larger areas (e.g. inside tubes)
• Rasped/filed away some of the chrome plating
• Rasped/filed to roughen up some of the glossy black plastic surfaces
• Applied paint thinner to roughen up some of the black glossy plastic surfaces (and to degrease some of them before painting)
• Applied black spray-paint to some small (non-black) areas 
• Roughened up my applied black spray-paint, to make it flat/matte.

For flocking, I used "decorative grade" type of flocking material for the telescope. While special telescope flocking material does offer freedom of shedding and less reflectance, but Honey Badger Don't Care and nothing can be cheap enough for my "Cheap Astronomy" series! After all, who would spend several dollars worth of flocking material on a 10€ scope? Right.

The material I use for flocking has a "sticky back" covered by protective paper (which has a grid on it and where you can draw with an pencil before you cut it).

One can use this flocking material in two ways:

• Either as intended, by cutting it, then pealing off the protective paper and sticking the flocking material where one needs it. If possible, degrease the surfaces first! And the more pressure you apply, the better the flocking material will stick – so initially just lay the material, then you can still correct the position, and then put down some pressure – without breaking things!
• Or in some places – like the inside of a tube – you can (after you cut the material) simply leave the protective paper in place, roll up the flocking material, and place it inside the tube. Simple as pie! Holds nicely in the inside of tubes (especially small ones), and can be easily removed if necessary. And if needed, you can still stick it inside the tube.

Reducing reflections of the focuser
When looking through the lens one could see two ring reflections, one from the shiny black plastic of focuser, and one from the chrome plating of the focuser's drawtube.

The drawtube reflection on my scope was totally brain-dead. The design of the drawtube seemed like someone had halfway thought it through. It has a internal baffle, and while the outside is chrome plated, the inside is painted in matte black – except the front end (objective end), were only a little bit of paint had reached it. So the chrome reflected the light back to the front lens. m(

After I grinded down the chrome from the front of the drawtube, cleaned the front up and spray-painted it black (and making the paint flat with a piece of wood, e.g. an pencil), the reflection seemed OK. (As I managed to get some of the glossy paint on the inside of the tube and ruined the original matte paint, I had to flock the inside – oh well.)

The glossy plastic of the focuser went matte as I cleaned it with paint thinner. And while this turns the black plastic slightly grayish, the degree of matteness is enough for me – while I initially intended to spray-paint it, I now could life without painting it.

Reducing reflections of the star diagonal
Now the star diagonal has a attached plastic tube (which fits in the focuser), which was wonderfully plated with chrome, a sight to be behold, truly marvellously produced – and totally brain-dead. First of all, the screw from the focuser's eyepiece-retainer had an burr and ate into the chrome. And secondly (and more importantly) the chrome plating created lots and lots of internal reflections.

To get rid of the tube's reflections I had to do two things: I painted the ends and flocked the inside.

To paint the ends, I rasped/filed away all the chrome from the exposed ends, and filed away all the copper underneath, until I hit the white plastic (don't forget to file of any burrs at the ends!). A little paint thinner prepared the plastic, and then I spray-painted the ends in black. After the paint started to become hard, I pushed a little piece of wood on it (e.g. an pencil), to make the paint flat/matte.

After the paint had hardened, I put some flocking material inside the formerly chrome plated tube.

Last was one little thing, namely the triangular glossy surfaces adjacent to the mirror – I cut out two pieces that matched roughly, attached them, and voilà!

Improving the star diagonal
Fixing the reflections from the triangular surfaces

Left: out of the factory, right: with added flocking material

Well, there are still surfaces causing potentially problems, but this has to suffice.

Reducing internal reflections in the Barlow
The barlow is composed of two parts screwed together. To get rid of the reflections I did the following:

• Unscrewed the Barlow
• Cut some flocking material to fit inside front tube (the rear tube is probably not so critical, so I didn't flock it)
• Rolled up the flocking material and slid it in (with the protective paper still on the back of the flocking material)
• Screw it back together

A daytime test of the worst combo – 3x Barlow and star diagonal together – showed an much improved contrast.

Flocking a dead horse?
Having gotten myself into a flocking frenzy, I went ahead and flocked the tube of the finderscope, as it was awfully glossy plastic. And having still some reflections inside the (tiny) eyepiece of the finder scope, I took eyepiece of the finderscope apart and and flocked the spacer between the two lenses of the (Ramsden?) eyepiece. Which did not remedy the reflections in the eyepiece (maybe an reflection on the eyepiece lenses?), but at least I felt good (pun intended).

The finderscope – A lost cause?
Unfortunately it seems that there are many things which are wrong with the finderscope. And its bracket.

First of all, no matter how much you clamp the bracket down, it will not stay aligned, mainly because the bracket was made for a OTA with an smaller diameter. m(

[Update] It seems the bracket holds a little better if you mount it the other way round – but only a little better. It still is an awful piece of shite.

(BTW, the finderscope bracket of my Newton scope was made for an OTA diameter that is larger than the Newton scope…)

A confounding problem with the finderscope's alignment is the fact that the finderscope's eyepiece (which can be screwed in and out to adjust for your eyesight) does wiggle in its thread. This finderscope seems like a school book exercise in uselessness.

The next thing was that while the lens of the finderscope was 23mm in diameter, the clear aperture was a measly 10mm. Bloody thieves! #§✰%!

But a small aperture (in a plastic housing) is nothing that a dedicated man (or woman) with a drill and a large drill bit can't fix! Having found in my belongings a 18.8mm drill bit (which comes out to 3/4 of an inch, or so I am assured), I fixed the "not enough aperture" problem – as stopping down an aperture, if necessary, is much easier than the other way round.

Having changed the finderscope from an 5x10 to an 5x19, I had to realize that this finderscope was stopped down for a reason: chromatic aberration. And lots of it. My (cheap, cheap) 7x60 binoculars look good in comparison. Maybe now one can do spectral analysis on stars simply by using the finderscope?

To track down the source of the finderscope's new found chromatic aberration, I tried the lens from the finderscope (which I assumed to be the culprit) with my H42mm eyepiece – no chromatic aberration. Then I tried the finderscope's eyepiece in the 300700 – no chromatic aberration. Whatever it is, I will put my money down on "intrinsically bad finderscope design" – some things are made too cheap even for my taste.

The short eye relief and small FOV of the finderscope did seal the fate of this scope: I hate this little piece of plastic.

[Update] After I fiddled some more with the finderscope and its bracket, I reversed the orientation of the bracket and was able to mount the finderscope somewhat stable on the scope. And to boot, I have been able to align it more or less –  this hollow victory came at a price, now the white paint of the finderscope is coming off in chips, revealing the black plastic… I don't mind that, but everything about the finderscope seems more or less brain-dead. And the finderscope still doesn't stay aligned.

[Update] I think I finally nailed the finderscope's bracket. Here's the recipe:

• Remove the two knurled knobs holding the bracket and remove the bracket – now you should have two M4 bolts sticking out of the OTA, each secured by 1 flat washer and 1 M4 nut
• Tighten both of the supplied M4 nuts (a bit) – don't break anything!
• Add 3 star washers (M4) to each M4 bolt
• Add 1 flat washer (M4) to each M4 bolt
• Put the finderscope's bracket on the M4 bolts, making sure the bracket slopes forward and the bracket's base touches the focuser
• Add 1 flat washer (M4) to each M4 bolt (here I used M4 washers with wider diameter)
• Screw on the two supplied M4 knurled nuts and tighten them – don't strip the threads!
• Done!

Now you should have the following sandwich on each M4 bolt (from top to bottom)

• 1 knurled nut (supplied)
• 1 flat washer
• Bracket (supplied)
• 1 flat washer
• 3 star washers
• 1 nut (supplied)
• 1 flat washer (supplied)
• OTA

 The sandwich

The plastic bracket now barely touches the OTA – the entire stability comes now from the sandwich of bolts, washers and nuts!

In case the bracket still doesn't stay put: Go to the first step, and add or remove star washers from the M4 bolts until the bracket seems firmly attached to the OTA. Another idea is to wrap electrical tape once (or twice) around the OTA, so the bracket rests on the electrical tape.

Furthermore, with some tape I managed it so that the finderscope stays aligned in the bracket. Victory! Not so fast, as the finderscope's eyepiece still wiggles – sigh. If I had a pot of "Chinese Grease", I might be able to do something about this problem… If everything fails, I will resort to some (weak) glue and glue that damned eyepiece in!

The doublet lens – and a blunder
One blunder I made was that I took apart the doublet lens between the two observation sessions and somehow reassembled it improperly. While I didn't notice it during the daytime, the sight of Saturn (on the second night, after I had reassembled the lens) was shocking: horrible, horrible coma. I took out the front element and carefully put it back in again – the coma was gone, thankfully all was well again.

Otherwise, there is nothing to adjust in the all plastic lens cell: Put in rear element, spacer and front element, screw in the plastic retainer to secure the lens – done.

BTW: The lens-cell seems to be permanently attached to the tube. Moulded? Glued? Who knows…

[Update] Fixing the base
The flexing of the base was really awful. The "focus shifting" I saw was actually due to this flexing. To fix it I did two things:

• Drilled a countersunk hole to add a countersunk screw.
• Added starwashers between the plastic base and the OTA (similar to the finderscope's bracket).

And furthermore I removed the protuberance…

 Only two screws hold the tripod base, and both are on the same side of the 1/4"-20 thread – the whole thing can flex. Also notice the protuberance.

Added a third screw (and sawed off the protuberance).

With starwashers and third screw, the connection to the tripod is much more stiff.

Saturn

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Now doesn't the colorful box directly invite the owner of this proud instrument to look at Saturn and his rings?

I had the pleasure to test the (modified!) 70/300 refractor on Saturn on the nights of the 30th June and 1st of July, and compare it with my first scope, an Optus 76/700 Newtonian reflector I got for 5€ (by now mounted on an EQ1 mount&tripod I got for 12.50€). These Saturn observations were the first proper observations of Saturn with an telescope by me, and in fact the first "real" astronomy I did with an telescope after viewing the Moon.

A few days later: Scorpius as high as it gets in our latitude, with Alpha Scorpius twinkeling in a orange light (and aren't the trees "beautifully" illuminated in orange by lots of high-pressure sodium lights?).

On the 30th June the night sky was simply beautiful, Scorpius rising high (considering the latitude) in the southern sky, a new moon rising in the NE sky some time after midnight. I would have stayed up longer for an observation session, but I had to retire to bed because my body ached and longed for sleep.

With a little help from astrometry.net

Saturn became visible in both scopes some time after sunset, while the sky was still blue. From my observation site I had not much time before Saturn vanished behind an hill (which blocks my view to the SSW). It proved to be enough time, as I could start while the sky was still blue. Anything but ideal observation conditions because of this, but then again I did see mighty Saturn and his rings for the first time with "my own eyes".

Granted, planets are not the prime target for such an fast refractor, but I wanted to see what is possible with this scope, and mainly I wanted to see Saturn for the first time through an telescope – and the planet was positioned favourably for me at the moment, so I looked at Saturn with both my scopes.

For comparison I used the Newton scope with an 10mm orthoscopic eyepiece (at 70x magnification), which yielded wonderful images of Saturn. Finding Saturn without an finderscope, only using a low power eyepiece in the Newton and the EQ1's setting circles was not easy, but possible – the setting circles are silvery metal, and the printing is shiny black, which makes reading them in low light conditions difficult. I roughly set up the equatorial mount (axis to 50 degree, pointing south) and Saturn's current position (RA axis to 20h46 for Saturn culmination when he is directly in the South, and an declination of about 10°) and then needed to "circle around" until I found Saturn.

Saturn and rings, according to Cartes du Ciel, currently with an apparent size of 17.8" and an apparent magnitude of 0.5.

In the Newton, Saturn with its rings was very sharp – with an "etched" feel to it. In the Newton at 70x (with the Ortho) I could not make out Cassini's Division in the rings, nor the small shadow Saturn casts on his rings – Saturn is still too small at 70x, I fear. As well, one could not tell where the rings stop and where the planet starts (and "which way round" the rings are currently). What's more, the mount (EQ1) did shake a bit on the wooden floor, and seeing was probably not ideal as well. None the less, Saturn offered a wonderful sight – I could have watched blissfully for much longer.

Simulated view (quickly created in Photoshop, not to scale): 
Saturn in the 76/700 Newton,
at 70x magnification, with the Abbe orthoscopic 10mm.
Small, but sharp, like "etched" – no ring details though, and no shadows visible

Obviously the slightest touch of the Newton (on its EQ1) lead to violent shaking, and focusing was difficult, but once the shaking died down I could see Saturn majestically floating by – until I had to readjust the RA axis, that is… I will have to give the EQ1 some more treatment.

After I had viewed Saturn for some time in the Newton, I turned to the refractor. Finding Saturn was difficult, as the sky was still blue and the finderscope did not offer any help. The Manfrotto/Bogen ball-type head is not the best one for adjusting a astronomical telescope while searching for Saturn. Having one equatorial mount where one could mount both scopes would surely be nice – but the EQ1 is barely adequate for the Newton alone…

Once I had the refractor on Saturn and started to use the Abbe orthoscopic 10mm eyepiece in it (which gave me a 30x magnification), it offered me a glimpse of what the "30070" could do. Very very tiny, but there it was: Saturn with an tiny tiny ring.

Using the H6mm eyepiece really surprised me. I expected some kind of "mush" (as the H6mm is noticeably worse, even during the daytime, than all the other eyepieces I have), but I could discern Saturn and the rings!

Arguably it did not offer the "etched" impression of the Ortho in the Newton, and the rings did not seem to form a closed loop (more like an attachment on the left, and one the right) – but here it was, Saturn with its Rings! It pays off to have low expectations, I guess. :-)

Simulated view (not to scale): Saturn in the 70/300 refractor,
at 50x magnification, with the H6mm eyepiece.
A tad bit smaller and dimmer than the Newton, and more blurred.
(In reality maybe a bit worse than this simulation,
more washed out and with some chromatic aberration.
The rings seemed like two attachments barely touching Saturn,
like the "ears" that Galileo Galilei described.)

Trying the Ortho10mm with the 3x Barlow did offer slightly larger magnification in the "30070" (90x times), but the view was inferior to what the H6mm eyepiece offered. As the supplied Barlow is not very good, one has to wonder what could tease out of this scope with the Ortho10mm and an good Barlow (or an good planetary eyepiece instead).

The combination of H6mm and 3x Barlow was impossible to focus – the shifting of the focuser the flexing of the OTA base (which connects to the 1/4"-20 screw of the tripod) becomes a real problem here.

Having established the Newton as "good", I wanted – for good measure – to try in the Newton on the one hand the H6mm eyepiece alone, and on the other hand the 3x Barlow with my eyepieces.

With some fiddling I managed to get the refractor's Barlow in the focuser of the Newton (by removing the eyepiece-retainer from the focuser-tuber, putting some tape around the Barlow). The Barlow now almost touching the secondary mirror, I got an image of Saturn. But no eyepiece yielded a good image – not the "no name" Huygens 42mm, not the CZJ Huygens 40mm, not the LOMO symmetrical 17mm and neither the Spindler&Hoyer Abbe orthoscopic 10mm (which are all otherwise good eyepieces).

Having forgotten to test the H6mm, I later tried it alone in the Newton as well – or at least I tried to try it. The Newtonian "not enough backfocus" syndrome reared its ugly head, and I was maybe one millimetre (give or take) short of being able to reach focus. I didn't think of removing the eyepiece-retainer at that time, which I want to try again next time. But what I saw of the H6mm did not persuade me.

Nearby star Kappa Virgo (at 4.2 visual magnitude) was visible in both the Newton and the refractor at low magnification – but not visible in the 7x19 finderscope.

Titan (at magnitude 8.8) was not noticeable in either scope, but then again I did not look for Saturn's largest moon (and the sky was not dark yet, as it was early evening).

Shortly before I went to bed I attempted to find the Andromeda galaxy with my (cheap, cheap) 7x60 binoculars (handheld, not yet mounted at that time), and thought that the "fudge" I found might have been it – as Andromeda will move into a favourable position over the next months I shall revisit it.

An Waning Crescent (&Terrestrial Use)

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As I woke up (way too early) at 4 in the morning of the 5th of July, I noticed a nice waning crescent in the eastern sky and put the scope to a short test:

• With the 10mm orthoscopic eyepiece (at 30x magnification) the Moon looked beautiful (but small), with just an hint of chromatic aberration
• The H6mm eyepiece (at 50x magnification) did show some more chromatic aberration (but much less than my cheap 7x60 binoculars), and yielded a image which was usable
• The 3x Barlow with the Ortho10mm was not good, but usable – the Moon is an much more forgiving target, it seems
• The 3x Barlow with the H6mm yielded an dark, but borderline useful image

Makes me once again wonder what a good Barlow, and/or good eyepieces with short focal length could tease out of this scope… I had too stop observing the Moon however as I had way too little sleep.

During the day the scope performed nicely with all my eyepieces (after I had the internal reflections removed, and focuser fixed, that is).

With the Sym17mm and the "1.5x erecting eyepiece", at about 26.5x magnification.

Same as above, but zoomed in by my point&shot camera. Can you see the cobweb? Notice how the rising heat stirs the air in the background.

Even the "1.5x erecting eyepiece" does offer nice views during the day. The usage of the "1.5x" comes at a price: the aperture gets reduced (which makes the "1.5x" useless for astronomy, except maybe for watching the full Moon), the eye relief gets reduced and the FOV gets restricted. What I can however recommend very highly in the "1.5x" for daytime viewing is my Sym17mm eyepiece (which is a "LOMO C15x" microscope eyepiece, which I bought used some time ago). Even the H6mm is borderline usable with the "1.5x" during the daytime (if only with objects directly lit by the Sun). Alas, my H42mm has a too wide field of view to be usable with the "1.5x".

The 3x Barlow produces significant chromatic aberration with all eyepieces during the daytime, only my H42mm had acceptable color error in combination with the 3x Barlow (yielding about 21x magnification – somewhat comparable to using my Symmetrical17mm alone, which has a wider FOV…). But if you need the magnification during the daytime, and if you can live with an dim upside-down image, and if you don't mind the color error, then by all means use the H6mm with the 3x Barlow during the day (or maybe on the Moon) – this will yield a nominal 150x magnification.

What's Nice & Pleasant About This Scope

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First of all, while I need to test it more (and get higher powered eyepieces and better Barlows), I think the lens in the OTA is very good. Everything else can be fixed or upgraded – but if the lens is no good, then what can you do?

So, I really like this scope – I think I will keep it as long as I have eyes to use it.

Regarding some minor details, there are some other nice things to note about it. The scope is lightweight. The metal OTA tube seems rock solid (no wonder considering the short length). The lens cap fits nicely. The dew shield fits nicely, one can even slide it out a bit (before it becomes too loose).

With access to microscope eyepieces one can get better low-power views. The scope has a 1/4"-20 thread for mounting it to a standard photo-tripod. Some of the baffling seems to be thought through (at least the parts of the baffling that are not brain-dead).

And did I mention it is cheap and (with some modifications) rather good?

[Update 2013-08-16] One thing I consider nice is that the supplied H20mm is apparently not of Huygens type. The H20mm eyepiece has its field stop before the field lens – this indicates that it is in fact not a Huygens type eyepiece. (The optics looks the same as those from the H20mm eyepiece supplied with my 76/350). Whether this eyepiece is a Ramsden or a Kellner eyepiece, I don't know. [/Update]

Under The Hood (&Measurements)

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[To be added in the future]

What Remains To Be Done

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More Testing
Duh. Of course I need to test this scope more. And use it. Maybe the Andromeda galaxy? Some double stars? One or the other Messier objects? Let's see what time, health and weather permit – I won't promise much.

The Finderscope Situation
I need a usable finderscope – but not the sorry excuse of a finderscope that came with the "30070".

While I think that once I fix the wobble of the finderscope's eyepiece, it might stay in alignment, it still has (with the aperture I increased from the meager 10mm to proper 19mm) horrible chromatic aberration. Furthermore the apparent field of view is small, and the eye-relief is short.

If I fix the eyepiece wobble (which seems doable), the finderscope might be "somewhat" usable (for some value of "somewhat") – I'll have to see if I can life with the remaining shortcomings of the finderscope. In the meantime I shall name it "Fienderscope, the gift from Tartarus".

The Focuser
After putting some thought into the focuser, it seems to work almost well up to 50x magnification, with shifting that is somewhat acceptable OK (but quite awful at 150x). [As it turns out the "shifting" is actually a flexing of the OTA base, which connects to the tripod – and is not firm enough. If I could afford some mounting rings…]

And the other shortcoming of focuser is that it still only accepts 0.965" eyepieces – instead of the 1.25" that is common today for such scopes (and most of the accessories one can buy).

Of course it would more than remedy this situation if I would go completely bonkers, and spend 79€ for an 2" Crayford focuser, to be able to use ultra-wide FOV eyepieces (which probably would require to remove the baffle in the OTA). This focuser would cost almost 8 times what I spent on the scope. And would not fit anyway, as it was made for and OTA with 72mm inner diameter…

I will try to go the "cheap&easy" route (our motto here at Cheap Astronomy HQ), and see if I can build out of wood an eyepiece retainer that will hold 1.25" eyepieces – should be doable. Once I have that, I can think about getting maybe an 8-24mm zoom eyepiece, or even an 1.25" Barlow (not the cheapest one, as one cheap and useless already came with the refractor – and nobody needs two cheap and useless Barlows).

[Update] The baffle in the focuser's drawtube (diameter of 15mm!) seems too small after visual inspection, and probably stops the scope down quite a bit. I will remove the baffle (or rather open it to 30mm, which is almost fully open) and see how much chromatic aberration this introduces (*crosses fingers*). Going to my "shop", and again stopping down the scope is always easier than opening such an baffle in the first place, as one has to take care of any reflective surfaces that one creates in the process. Plus, if I add a stop again, I can see how much stopping down is necessary by making two or three baffles to test.

Brain-dead drawtube: The dark black part is the flocking added by me, the gray part is the original paint (with the 15mm baffle already removed by me).

Halfway thought-through: The baffle of the OTA – it is matte, but it is gray compared to my flocking material.

[Update] This scope is stopped down!
I determined that the baffle in the OTA stops the scope down. I removed the baffle in the OTA and I shortened the focuser's drawtube by about 15mm. This helped increase the clear aperture and I finally see some color aberration! During the daytime, one can see out of focus slight blue halos, which vanish in of focus. But the small diameter of the focuser's drawtube and the intrinsic small diameter of an 0.965" star diagonal will stop down such an fast scope. For such an fast scope, one needs an 2" diagonal diagonal of at least 1.25" and an focuser with an drawtube that has an clear aperture that is larger than 1.25" (as the drawtube's "front end" is somewhat closer to the lens – duh!). Obviously a 2" focuser and 2" diagonal would be the right combination for such an fast scope – a drawtube with an ID of about 1.25" (as is typical for such an Chinese-made plastic focuser) is too small.

The more I think about it the more I come to the conclusion that the best thing will be to build a simple DIY crayford 2" focuser. While everything else I done to this scope was a series of "simple fixes", this will constitute actually building something. Let's see what I will do.

[Update 2013-07-13] I roughly calculated the needed clear aperture for D=70mm, f=300mm and FOV=20mm (fully unobstructed optical path, so every "point" on the field lens of an eyepiece sees the whole objective lens). It is worse than I thought:

• For the baffle in the OTA (roughly 85mm from the lens) I calculated a needed clear aperture of roughly 55mm – the baffle had an clear aperture of 35mm. o.O
• For the focuser's drawtube front end (very roughly 110mm from the lens) I calculated a needed clear aperture of roughly 52mm – the drawtube has an inner diameter of 32mm. o.O
• At the baffle in the drawtube, the needed clear aperture is about 42mm – the baffle was 15mm. o.O
• At the front end of the star diagonal, the needed aperture is about 38mm, but the 0.965" star diagonal has (with flocking) an inner diameter of about 18mm at its front end. o.O

With the baffle in the drawtube, I calculated (which may be wrong) that on-axis the effective aperture was only 30mm! With that one baffle removed, the effective aperture rises to about 50mm, which is still meagre! And while the baffle in the OTA decreases a little bit from the clear aperture, the bottle neck now is clearly the 0.965" star diagonal (closely followed by the 0.965" focuser).

I'm afraid, it is: 2" focuser (with 2" star diagonal) – or bust.

Flocking the dew shield
And I think I will flock the dew shield, which I forgot in my flocking frenzy – might be a good idea, as the dew shield is made from very shiny plastic.

Lens and lens cell
Something that might be further beneficial is to blacken the edges of the lens, as the lens cell is shiny black plastic.

The front part of the lens cell (the "retaining ring") might benefit from flocking as well, as one can see that shiny black surface when looking without a eyepiece through the scope.

Better connection to the tripod
The base of the OTA, which connects to the tripod via a 1/4"-20 screw can and will flex. The best (but not cheapest) would be to remove that base and use telescope mounting rings instead. I will see if I can come up with a cheap solution for this problem.

Done! See update above!

tl;dr

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• Refractor telescope with D=70mm (2.75 inch) and f=300mm (f/4.3).
• The one I got was out of the box useless for astronomy.
• The scope is stopped down. Out of the box possibly to only 30mm (if not slightly less). This can be raised with one modification – removal of the baffle in the drawtube – to maybe 50mm (or somewhat less). Some sources of reduction in clear aperture are somewhat easy to fix with DIY skills (remove the baffle in the OTA, remove the baffle in the focuser's drawtube), some (drawtube is too long and especially having an a diameter that is too small, and a 0.965" star diagonal is too small) are impossible to fix and need a bigger solution (basically adding a 2" focuser and 2" star diagonal). A 0.965" focuser and a 0.965" star diagonal are incompatible with such an fast scope! Such an fast scope needs an 2" star diagonal to use the full aperture.
• The accessories (eyepieces, Barlow) are not good, but somewhat useful.
• The star diagonal is after modification somewhat useful (but has still too small inner diameter).
• The usefulness of the supplied 5x10 finderscope is very doubtful.
• The bracket for the finderscope has the wrong dimensions and will not stay aligned needs much care and attention to be attached properly.
• After I applied some modifications to the scope and star diagonal, the optics performed rather nice (given my low standards).
• Furthermore, the scope benefited greatly from good eyepieces and a good mount/tripod.
• It would be fabulous to test this scope with good 2x and 3x Barlow lenses (and good eyepieces with short focal length). This might even make this an small planetary telescope (to be determined).
• The focuser accepts 0.965" eyepieces, which makes upgrading difficult (unless you have an extensive collection of 23.2mm microscope accessories).
• Might make a nice and cheap rich-fielder, scope for travelling, finderscope, guiding scope (with some more upgrades).
• My fantasy: Fitting the scope with an 2" focuser and trying it with some good accessories (e.g. wide view eyepieces).
• I might be wrong, but my impression is that the OTA was not made by the same factory that supplies the omnipresent Synta/Skywatcher/Celestron/Orion scopes, but by an (in these parts) hitherto unknown Chinese manufacturer – so there seems to be another factory in China making cheap scopes! Per chance in Ningbo? (The eyepieces, Barlow and "erecting eyepiece" however seem to come from Synta, I would guess).
• On a personal note: Writing this down takes longer than actually doing the modifications and tests…

So, this must suffice now.

[Update 2013-09-25]

I finally managed to mount the 2 inch diagonal somewhat better and did some tests (daytime, as well as Moon). With a 25mm SPL (12x magnification) and 20mm PL eyepiece (15x) the lens gives a nice image – seems almost usable. With a 12.5 SPL (24x) and 10mm PL eyepiece (30x) the image shows some chromatic aberration and quite a bit of astigmatism (one can either focus on horizontal features, or vertical features…). With shorter EFL (nominally 6mm and 4mm, giving 50x and 75x magnification) the problems get worse (obviously).

I don't know where the source of astigmatism is. I don't have any means to properly collimate this rig – and even if I could, it would not help much, I'm afraid. To adapt the 2"-diagonal I used a PVC-tube that has some flex – but the flex from this PVC-tube pales in comparison to the flex coming from the plastic-housing of the diagonal and from the plastic 1.25" adapter (you get what you pay for, I guess). Though having a wide field scope with 12x magnification (5.8mm exit pupil) is OK.

As a finderscope this thing is probably too unwieldy and too heavy (and I wouldn't know how to adapt it for e.g. my 70/700 refractor anyway) – however as a wide-field companion on a photo-tripod this thing is nice.

Speaking of astigmatism: When disassembling and reassembling the lens, one needs to take care that the spacer, front and rear element of the lens are put in properly. I found this "technique" helpful:

• Put in the rear element (alone) into the "lens cell" and make sure it is properly seated.
• Next put in the the plastic spacer, and make sure it is properly seated as well.
• Finally put in the front element. Make sure not to tilt the front element while you put it in! If you tilt the front element while putting it in, it is possible to move the spacer a bit, which will result in the front and rear elements being tilted to each other – a much much worse image will be the result.

I found it helpful to do this while the scope is horizontally.

[/Update 2013-09-25]

[Update 2013-10-11]

Success! I finally managed to turn this scope into something useful! Now it works quite well when I tested it with my PL25mm (12x magnification) and PL20mm (15x) eyepieces. With my PL10mm (30x) the image deteriorates somewhat but is borderline between useful and not-OK. And with the PL6.5mm (46x) the image quality clearly deteriorates (no longer sharp, quite a bit of chromatic aberration). This is now (for me) a useful wide-field scope for magnifications of 15x and below, which nicely completes my scope collection.

These are the things I changed (maybe someday I manage to make more images):

• Into the 2-inch PVC tube (which holds the 2-inch diagonal) I put another PVC tube. Now the assembly is more stiff and can be better adjusted (I wouldn't dare to call this "collimation"). This tube has the effect of slightly vignetting the lens.
• I put small strips of aluminium foil tape (1/10mm thickness) on the edge of the lens elements. Per lens element I used three strips (120 degrees apart). Each strip is on the side of the lens and goes around to the rear of the element. So the contact between the rear element and the plastic "lens cell" is better, the contact between the front element and the spacer is better and both lens elements are better centered. (BTW: Putting together the lens was much easier this time.) I tried it first with only the aluminium foil (without the white plastic "lens spacer ring"), but the image was decisively "not good" – with the spacer it was much better.

By using a Barlow the image improves a bit at high magnifications – maybe the Barlow acts as a stop? Or is it the reduced focal ratio that make the life of the eyepiece easier? And using the lens cap to stop down the scope the image quality improves significantly at higher magnification (but is obviously dimmer). So with/without the lens cap one could use this maybe as a finderscope / wide-field scope combo.

I still wonder: Am I the first person to use the lens from this scope at its full aperture? I still don't know how good the lens itself is – that would require a proper lens cell, and determining the right space between the lens elements – but the lens could do a lot more than what is possible out of the box (or conversely a 30mm f/10 scope would be much small/lighter/cheaper with the same performance as this scope had out of the box).

Anyway I ordered a cheap PL32mm and PL40mm, these will be nice for this scope I imagine.

Stay tuned.

[/Update 2013-10-11]

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[2013-07-05: Published]
[2013-07-06 to 2013-07-12: Various updates]
[2013-07-13: Added information about clear aperture]