Quote Originally Posted by Mod View Post
Thanks Mik - a friend just showed me a minty example of a three draw civi scope dating from 1918 as far as I recall!

Can't focus and much dust and cack when you look thru the ocular.

Suggestions on cleaning techniques and materials - specifically, are there any 'no no's ' to observe?

rgds Mod
If it won't focus it's possible there are missing lenses. What I've once found is that only the front lens of the invertor was in place because that can be screwed back on its own without its brass sub-tube and second lens. I guess that's what can happen if kids are left to play with a scope and the adult doesn't know what bits there should be where. You'll need to find an approximately similar scrap telescope to replace them - I've done this a number of times - but before you ask, I've no spare lenses kicking about at present - sorry .

It's also possible some cement in the objective has gone opaque, but you should see that straight away looking into the front end. If that's so, unscrew whatever holds the lens group in and put the lens in warm water, gently and very gradually heating it until the cement melts and you can separate the lenses. Don't be impatient; it can take a while for the lenses to warm through.Then wash the stuff off in the same hot water. When I've separated lenses this way I've found it works just as well without cement.

There aren't too many no-nos so long as you're reasonably careful. You can't usually reassemble the invertor or eyepiece wrongly (so long as you have all the bits ), and I just use ordinary specs cleaning fluid and one of those lens cloths. Obviously don't rub hard or forcefully.

The objective lens can actually take quite a bit of damage. Light diverted by scratches and gouges simply never reaches focus so tends to dim, rather than blur, the image. The front invertor lens, as I said, is very close to focus, so any damage to that will show very obviously in the image.

Regards,
MikB