Cleaning the inside of eyepieces and barlows

[jnb]

How can I best clean the inside of a barlow?

I have a cheap stock barlow lens that I was trying to use on Saturday. I wanted to barlow my 8mm BST for use on the moon as conditions were good enough that I thought that I could push the magnification. As soon as I added the barlow I could see spots over the image, without the barlow it was fine.

The spots may well be my fault as I was drilling a hole in it earlier (the screw hole to clamp the eyepiece had stripped the thread) but the thing is glued together so I had to drill next to the lens rather than disassamble and then drill, the process hasn't left any obvious visible marks but it is a little difficult to see inside the barrel to check. It's a cheap barlow so I'm happy to take risks with it but what's the best approach to cleaning it?

[great_bear]

The Barlow will narrow the exit pupil, showing spots on the eyepiece that were not previously noticeable.

To be sure its the Barlow not the eyepiece, secure the Barlow and rotate the eyepiece in place. If the spots rotate along with the eyepiece - well - you know the drill (literally, it seems).

For cleaning, most optics can be disassembled completely. The trick is figuring out how to do so without everything falling out everywhere - not just the issue of chips or breakage, but the risk of things coming apart too quickly to see how to reassemble things. Only "specialist" tool required is a blower (cheap at £3 or thereabouts)

Best cleaning solution is Acetone, but it's tricky stuff - you don't want that coming into contact with anything other than glass, tissue, or cotton bud.

Lots of good quality tissue and cotton buds are the order of the day, and NO RUBBING (just gentle sweeping without applying additional pressure)