Name that optic

[Highburymark]

I have a pair of Zeiss microscope eyepieces for binoviewing - model: OPMI 10/22B with T coatings. I’m intrigued about the optical design. There’s a long thread on CN which delves into the fascinating world of Zeiss microscope EPs, during which one contributor says it’s a triplet design (see drawing of cemented triplet - sketch by Madrid Sky). Does anyone know what this design is called? Can it be classified as an adapted Abbé ortho? It’s certainly super sharp and bright, but has a wider (50-55 degree) fov than a classic Abbé. 

[John]

If the bottom surface of the triplet element is concave then it seems to be very similar to an abbe orthoscopic design. There was a konig design that also used a singlet-triplet configuration but the bottom surface of the triplet in that one was concave. I think the triplet might have been the eye lens in that design but it's a little unclear from this illustration:

Edited October 31, 2020 by John

[Highburymark]

Thanks John. Not easy to distinguish between some of these early modified designs. The sketch I posted looks like it has a slight concave shape at the bottom of the triplet, unlike the convex design you posted.

[John]

31 minutes ago, Highburymark said:

.... The sketch I posted looks like it has a slight concave shape at the bottom of the triplet, unlike the convex design you posted.

I agree, which would suggest an abbe orthoscopic based design modified to permit a slightly larger well corrected field ?

Rather like Al Nagler did with the plossl.