Finally got a Zeiss stereo!

[Scarodactyl]

I've had the chance to handle a lot of stereos over the past few years, including almost all the major brands, but Zeiss had eluded me.... until now!

I got a great deal on a Discovery V.8! It's a handsome unit, equipped with a 1x achromat objective.
First impression is that it's very light--there's probably a lot of empty space inside, not that that's a problem. It handles well and feels like a quality item.
I'll admit I'm a bit surprised they sell these with achromat objectives though. Maybe I am spoiled (I definitely am) but it feels a bit weird for a microscope which costs as much as this one does new (Check this one--10k new with a planachro 1x! It does come with a very nice base too though) to have doming distortion at 1x that feels just as pronounced as the original Wild M3's. Maybe this would matter less on a three-dimensional subject vs a flat one. That said, while it does show the somewhat pronounced axial CA that's typical of stereo achromats, lateral CA (typically pronounced on a CMO achromat) is actually very well controlled and the image resolution is sharp from the center to the edge. So while it's definitely an achromat it's not a plain 'ol achromat I guess, though I'd have prioritized the distortion a bit more (or rather, I would not have offered a non-plan achromat at all, not if I wanted to be the primo brand--I would have made sure if you're paying that kind of money you get at least a plan fluorite-type experience).
Alas, higher-tier Zeiss stereo objectives are insanely expensive on the used market even by CMO objective standards. The objective does have the same m60x1 thread as the Wild M8 and Leica M50/M60/M80. As it happens I currently have an M8 which I'm slowly turning into an engraving scope (by that I mean 'I'm waiting on a custom objective adapter'). Unfortunately the thread on the Zeiss body is kind of shallow and the thread on a M8's 1x plan objective won't engage, but the Zeiss objective can be mounted on the M8 just fine. I need to do some proper testing for optical compatibility on that tomorrow.
Overall it seems like a nice scope, just very rarely available at a reasonable price. Unfortunately higher tier scopes in the line have motorized components and are probably not going to be great for hobbyists or reliably in the long term like a mechanical scope. Anyway I'd definitely recommend the V8 overall, but while I like it and it feels really nice to use it doesn't exactly blow my socks off either with the achromat. We'll see if putting another objective on is feasible.

[imkap]

Thanks for sharing...

[Scarodactyl]

Messing around with it some more. The zeiss achromat performs very similarly on my Wild M8, and handholding the m8 objective on the discovery performs much like ir does on the m8 but with a magnification of about 0.75x. A nikon smz-u cf plan 1x on the zeiss is much like the m8, and a smz clone 1x plan performs similarly to the wild m8 or cf plan objective but with more CA. Same magnification on all three. Handholding a leica m65 plan 1x performs much like the m8 plan 1x but at a magnification of about 0.92x. My m10's planapo 1x objective gives great planapo performance with the same 0.92x magnification.
I also tried an olympus df plfl 1.6x which gave a mag of 1.35x with a bit less ca than the wild 1x.

The reference focal length for the m8 is 100mm, and 80mm for the m10, so we can infer a reference focal length of somewhere around 75mm on the Zeiss. In a sense the whole system is optimized for high mags, with a higher NA and shorter working distance on the designated "1x" objective which would be a 1.33x objective on the wild m8 or nikon smz series.

A 65mm plan or planapo objective could be used with an off the shelf Leica adapter meant for adapting them to the M80 line, and would give good results at a lower cost than a Zeiss planapo. Or conversely if a Zeiss planapo falls into your lap a Wild m8 or Leica m80 might do it justice without any adapters.

Overall I'm struck by how compatible these objectives seem to be. I'd had discouraging results from informal hand held testing on eg putting nikon objectives on a wild m3 body but I am thinking I must have been holding them poorly. I also once tried an objective from a Zeiss smartzoom which obviously required incredibly strong compensation, showing unbelievably strong CA on a non-compensating system so I was worried that would translate to their stereos. Apparently not.

I printed an adapter to put nikon style m58x1.25 objectives onto m60x1 bodies. Unfoetunately due to mechanical logistics the objective has to sit a bit lower than the m60 threads. On the s8 a generic plan 1x and plan apo 0.5x had a bit of edge vignetting on the putside of the FoV (left side of left eyepiece right of right) at minimum mag (nominal 1x) which went away at 1.25x. The nikon 1x did the same but worse on the m8.

[Scarodactyl]

Final configuration:

The Nikon 0.5x HR fills the entire 23mm eyepieces at minimum mag and gives nominal ~0.46x magnification. The reference focal length for the Nikon smz1500 is 80mm so it all tracks. There is a touch of field curvature at minimum mag but otherwise it works great.

[PeteM]

Thanks for trying and reporting all those options, Stephen.