Here's a fun one?

[TheThing]

Anyone seen anything like this before?  It was in my box of astro bits and I cannot recall anything about it, having bought it etc.

Its metal construction with nylon screws and solidly made.  The lens in it seems to be magnification of some sort, although holding my phone camera to it doesn't yield very clear images.  I assume it is to go over the top of an eyepiece but to what purpose?  A kind of Barlow maybe?  No identifying marks or features on it.

Any guesses?

[Louis D]

If this were a stereo microscopy forum, I'd guess it was an auxiliary magnifying lens to fit over the objectives, although the optics seem a bit small in diameter for this purpose.

Any idea how you came to possess it?

[TheThing]

No sorry.  I think it may have come with an old telescope, possible a Tal 1 but I'm not sure.

[Carbon Brush]

Have you put it on a scope (daytime is fine) and tried the view? In particular rotating the extra part.

I'm wondering if it may be an astigmatism corrector. Or maybe it is a polarising filter?

[Don Pensack]

Or an accessory lens to extend the eye relief.

Or a lens to lengthen the focal length.

Some experimentation is in order.

[markse68]

Maybe part of an old film camera focussing aid?

Mark

[TheThing]

Great ideas, thank you.  I'll try it.out tomorrow and report back.

[TheThing]

Ok, so have tried it out in the day.  As far as I can tell, it does not magnify the image through an EP at all (used with my trust Tal 40mm plossl).  It simply makes the image look like there are lines running across it, a little like the blurry image taken directly through the lens but, with the image in focus. 

I'm stumped!

[RT65CB-SWL]

If I get the the correct answer, do I get to keep it? 🤣

I am being serious now... Looking at the second image, I think it is a diffraction grating that fits over the eyepiece? 🤔... I have seen the item somewhere, but cannot remember when and/or where and that is so damn frustrating! 😬

Edited October 11, 2022 by Philip R

[Louis D]

26 minutes ago, Philip R said:

I am being serious now... Looking at the second image, I think it is a diffraction grating that fits over the eyepiece? 🤔... I have seen the item somewhere, but cannot remember when and/or where and that is so damn frustrating! 😬

Building on that, try focusing/pointing on/at a fluorescent light fixture, and then put it over the eyepiece to see if you get a spectrum with a few prominent emission lines:

[TheThing]

By Jove, I think you've got it!  I've only got a small head torch to use but, at certain angles, I can get a glimpse of a tiny image exactly like Louis D's post.  I used to have a Star analyser many years ago, probably bought after I got this item!  I might give this a whirl next clear night and see what it produces.

Thanks to all who responded.  Very much appreciated.