This is a problem I've recently run into while setting up my dad's microscope. I got him a nice SZ7 with a trinocular port, but I wasn't sure how to attach his camera to it (in this case a canon EOS Rebel XS).
If you have the original sz7 trinocular port that has a threaded hole then what you need is a particular B&L threaded tube that accepts a 23mm eyepiece at the top. This is now just a third ocular, so you can use standard eyepiece adapters for a c-mount camera of choice, or a 23mm projective eyepiece and a standard microscope to camera adapter with a ~1" clamp.
Most SZ7s on the market, however, seem to come with an unthreaded trinoc mount. This one accepts a smooth 27mm tube that is held in place with two set screws. It looks like this:
Optically it's exactly the same, but as far as I know Bausch and Lomb didn't make an eyepiece tube to fit it. They had a few purpose-specific adapters, I believe mostly for polaroids, which are scarce and probably not useful anyway. This guide is for making your own eyepiece tube, and on top of that how to attach a DSLR to it.
What you need:
A bunch of M42 spacers, order at least 5 of those sets of three just to be sure (~$3.50 per set $18 total) --I'll try to get a tally of how many are used on the final version later
1 M42 female to C-mount Male adapter (~$15)
1 male to male m42 adapter (~$5)
1 m42 helicoid (or 2 optionally) (~20/ea)
1 27mm od 25mm id carbon fiber tube end protector (~$4 for 2)
1 ocular off a broken b&l stereozoom (variable, don't spend much)
1 b&l stereo 10x eyepiece (for testing only, use one from an ocular)
For a DSLR: 1 Nikon 2.5x projective eyepiece (I typically pay about 40 dollars for a used one)
For DSLR: 1 m42 adapter for your camera (~$5)
Total estimated cost ~100ish dollars, depending. That is sort of a lot for a self-made solution, but given what a commercial one costs (eg https://www.martinmicroscope.com/produc ... icroscope/
) it's not bad--and I suspect the results are as good or better.
For the first part, a 27mm tube to m42 adapter, I found a very handy part on eBay. This is a metal cap that is slipped into the end of a carbon fiber tube to prevent the ends from fraying. Its outer diameter is 27mm and its inner diameter is 25mm. These are available very inexpensively, here is one for example.
They fit perfectly in the trinoc port. Also conveniently, the inner diameter of 25mm is just about the diameter of a male c-mount thread. A standard male c-mount to m42 adapter almost fits right inside.
All it takes is a bit of modification to get them to fit together perfectly (this could be done with sandpaper, but I used a bench grinder because it's faster)
A bit of JB-weld and they're stuck together forever, and you can now attach standard m42 spacers and dslr adapters to the port. You'll need to add the male-male m42 adapter here to get male M42 threads facing up (as most m42 dslr adapters accept a male m42 thread.)
All you need now is a convenient way to hold an eyepiece in the middle of those spacers. As it turns out, the ocular off a b&l stereozoom microscope--any stereozoom, 1-7--fits perfectly inside a standard m42 spacer, well enough that you can just let it sit in there and not further secure it even for a microscope with a tilting base.
So just attach an appropriate length of m42 spacers between these two parts. It needs to be about 5 inches from the base to the ocular, but you can tell you have it right by getting a nice bright subject under your scope in sharp focus, putting an eyepiece in the ocular and adjusting the length until the image in the eyepiece is in focus. I found I got close enough by using normal spacers, but it could probably be improved by adding a helicoid for fine-tuning, as it is pretty sensitive to getting this length correct.
Once the b&l eyepiece is in focus you can now use a standard eyepiece adapter for your camera of choice. I haven't done much with smaller c-mount cameras so you might be able to remove the ocular entirely and do direct projection with an m42-cmount adapter.
If you want to use a DSLR, put a Nikon 2.5x projective eyepiece in the ocular. Then add more m42 spacers above with another helicoid and an appropriate m42 adapter for your camera. Add/remove spacers and adjust the helicoid until the image in the camera is in razor-sharp focus.
Typically the 2.5x is good for full frame and works on aps-c with a bit of cropping.
The end result looks awfully tall, but it doesn't seem to have any problem with being tilted, and the vibrations aren't too bad.
I suspect the trick with b&l oculars inside m42 spacers should be useful in a number of cases where original adapters are unavailable or expensive.