Adapting non-OEM lenses to CMO stereo scopes

Everything relating to microscopy hardware: Objectives, eyepieces, lamps and more.
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PeteM
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Adapting non-OEM lenses to CMO stereo scopes

#1 Post by PeteM » Thu Mar 02, 2023 7:18 pm

In what should have been evident to me a few years back (but wasn't), it's often possible to re-purpose other brands of stereo microscope objectives to the CMO scope of your choosing. Stephen was the one who alerted me to this. It's easy enough to roughly test compatibility by hand-holding the objective in place and making up a thread adapter.

This could allow many of us to get wide zoom range stereo scopes at more affordable prices.

In this case, I wanted to complete an affordable Olympus SZH scope without paying hundreds for used OEM objectives. The SZH has a thread diameter of M54 x 1mm. Pictured are an unknown (anyone recognize it?) 150 mm focal length objective, likely from a surgical scope, and a Nikon Plan 1x with an M58 x 1mm thread. This was initially meant for the Nikon SMZ 800/1000 series.

The cheap but likely achromat 150mm working distance objective has a roughly M67 x 1mm thread, adapted to M54. It gives about a .67 magnification and is parfocal from about 5x to 42.5x on the Olympus.

The Plan 1x Nikon objective has a stated numerical aperture of .105 at 80x, which apparently beats the stated 0.087 numerical aperture of the original SZH DF 1x Plan Apo and the .090 numerical aperture of the earlier Nikon 1x ED Plan. It could be that's an apples-to-oranges comparison. In any case, the Nikon, with a working distance of 78mm, loses 3mm in working distance to the Olympus Plan Apo (81mm WD) -- but it was cheap and available. It works beautifully and has the added advantage of taking widely-available 55mm filters, polarizers, wave plates, protective lenses, etc.

I've also adapted random objectives to Wild M3Z and M8, Leica MZ6, and Nikon SMZ-U scopes - with all able to be made parfocal and with no obviously introduced aberrations. That's not a guarantee, but most of these CMO scopes seem to have an infinity portion without much in the way of corrections in the tube lens or eyepieces.

Options for making up an adapter include turning one on a lathe, 3D printing, or buying a bespoke one. Camera and telescope thread adapters are often available in the needed sizes, making it possible to make up simple tubes and then epoxy the threaded adapter in place.

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SZH with adapted objectives.jpg
SZH with adapted objectives.jpg (125.72 KiB) Viewed 598 times
SZH thread adapters.jpg
SZH thread adapters.jpg (140.02 KiB) Viewed 598 times
Last edited by PeteM on Wed Mar 29, 2023 9:12 pm, edited 1 time in total.

apochronaut
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Re: Adapting non-OEM lenses to CMO stereo scopes

#2 Post by apochronaut » Thu Mar 02, 2023 10:58 pm

Several years ago, I added a 17.00 .5X aux. lens to an AO 580. The metric thread which I think was 48mm was close enough to the AO imperial measure threads to go in for about 4 turns. It works fine but pushes the focus to the very end of the rack. As you say though, I can't see any major negative effects of the add on : just over the top w.d.

Scarodactyl
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Re: Adapting non-OEM lenses to CMO stereo scopes

#3 Post by Scarodactyl » Thu Mar 02, 2023 11:39 pm

I think it must be much harder to engineer a zoom or step mag system with very correcting eyepieces or tube lenses, since that seems to be how they were designed even way back when. That isn't universal--I've tried a Zeiss prozoom apo objective which obviously required ultra strong compensation--but every stereo objective I have tried has given reasonably well corrected results on other bodies, aside from vignetting issues depending on the reference focal length.
That all said I have barely done any real experiments with this, so I'm glad you've actually given it a serious test and had good results!

PeteM
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Location: N. California

Re: Adapting non-OEM lenses to CMO stereo scopes

#4 Post by PeteM » Fri Mar 03, 2023 12:20 am

To add detail - the two adapters shown were machined out of aluminum. Of the four metric threads, the 58mm was scavenged from a camera filter adapter and epoxied in a pocket. That approach should work with 3D-printed parts as well. Three threads were approximated on an inch-thread lathe and cut a bit loose to fit.

After a quick bead blasting, Birchwood Casey's "aluminum black" was used to blacken the surfaces. It's not nearly as good as black anodizing, but quick, cheap, and better over threads than paint would be. If reflection were a problem, probably best to go over inner surfaces with dead flat black paint.

Surprisingly, an old Kodak Extagraphic slide projector lens, turned down and threaded to fit, made a usable lens for the Wild M3-7-8 series. Not superb quality, but good enough to be used and abused by kids. The shorter focal length Kodak projector lenses also become excellent LED-illuminated magnifiers when married to a "selfie" ring light.

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