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).