AO x20 objectives

[Photomicro]

I am sure there is a sensible explanation for the fact that I have two AO x20 objectives, both phase, and both plan ache NA 0.50 types.

However, on my AO 10 and AO 20 one performs much better than the other.

The better performing one is Cat No. 1212 and the leseer of the two a Cat No. 1223.

They do look different externally, but both are clean, and looking through the poorer one with a lens, I cannot see any problem.

So, I am wondering if one was designed for a later stand.

Any ideas?

[Photomicro]

I think I have the thing sorted now, via a rather peculiar route but started by someone outside of the forum suggesting this objective was one for the inverted Biostar model.

I hadn’t sussed that the optic was from an inverted, so that was a bonus. Someone mentioning the Biostar Inverted had me looking at the P S Neely site. Whilst a catalog and manual are listed, they are not links, so that didn’t help. I did find such elsewhere, so I do know what such a beast looks like now.

However, whilst on the Neely site, I realised I had not searched there for the objective Cat. No. despite doing so from numerous documents I had d/l some time ago, On doing this, I spotted this;

1223 20x Phase Achro or Plan Achro 0.50 1.1 Inf. 34 1.0mm Cover Glass Correction

This last part had me thinking. I knew it didn’t have a collar, so wasn’t adjustable, as some are on inverted optics.

So, I set the lens up, with a diatom strew I know well, and saw the rather hazy, muddy image seen previously. You have probably guessed the next bit. Flipping the slide upside down resulted in a contrasty, sharper and clearer image !