Nikon 50x 0.80

[Saul]

What is the difference between these two Nikon 50x 0.80 objectives ?

https://i.ebayimg.com/images/g/mYMAAOSw ... -l1600.jpg
https://i.ebayimg.com/images/g/RqkAAOSw ... -l1600.jpg

Thanks,

[Sym P. le]

Simply put, the first one, EPI, can pass illuminating light through the center of the objective, whereas the second, BD, passes illuminating light around the objective in their designed intent. The EPI is slimmer, though the case of the BD might be removed to utilize the slimmer central lens structure. Both are infinity objectives, which require a tube lens to focus the image.

[Saul]

Simply put, the first one, EPI, can pass illuminating light through the center of the objective, whereas the second, BD, passes illuminating light around the objective in their designed intent. The EPI is slimmer, though the case of the BD might be removed to utilize the slimmer central lens structure. Both are infinity objectives, which require a tube lens to focus the image.

Great, thanks !
Optical design is the same ?
Can pass illuminating light through the center of the objective in the BD version also (using custom design) ?

[Sym P. le]

I can't speak to the optical design. I didn't intend to imply that a BD objective is a practical substitute for an EPI. I can only imagine horrible internal reflections, even if coatings, or lack thereof, are the only difference.

[PeteM]

In my experience, makers often use the same lens arrangement for their brightfield epi objectives (light reflected down to the specimen and up to the eyepiece through the central core) as for the epi darkfield. Those just add a channel around the same or similar lens core for a ring of darkfield illumination.

Users typically want the option of both brightfield and darkfield illumination in the same BF/DF objective. What will often change is the thread mount, to accommodate the larger diameter barrel. FWIW, the early Leitz/Leica BF/DF epi objectives managed to fit their BF/DF objectives in an RMS mount.

[Scarodactyl]

Thr 'B' in 'BD' stands for brightfield after all. These objectives work just as well in epi as their non-BD counterparts, they just also do darkfield. The lens design is theoretically the same but in practice who knows. They seem to perform the same.

The cf plan objectives are generally pretty good. They're fluoriteish in corrections, lateral CA is not bad but they do have some axial.