LOMO PO501-1 100mm f/2
The lens being adapter here is a LOMO PO501-1 100mm f/2 lens from a 35mm cinema projector, manufactured in Soviet era Russia. You would have found lenses like this on projectors in cinemas in small towns across the Soviet Union in the 1970s and 80s. As such it is a big hefty lump pf glass: the lens itself weight in at around 700 grams, and the complete lens weighs in at around 970 grams. Both the lens and focussing helicoid I used are big enough to make the combination a bit of an ergonomic nightmare! In particular there isn't enough room for your fingers between the cameras hand grip and the focussing helicoid. Are the results worth it? Well in a word, no! But that is because this lens turned out to be in rather poor condition. The coatings in particular have decayed and this made the results extremely soft and "glowy" (to use the technical term!!). But I think a better example of this lens would have the potential for really interesting results, so I have decided to document the adaption process in case it helps someone who has that better example. (I might get one myself in the future!)
Here is everything I used to adapt this lens:
A focusing helicoid designed to mount an M65 screw mount lens on an M65 screw mount camera with a extension range of 22-55mm.
As usual you can find these focussing helicoids on both Amazon or eBay
62.5mm clamp to M65x1 male thread adapter
You can see from the photograph above that the lens barel is a simple metal tube with the same width along it's entire length. This means there is no wide bit at the top to rest against the end of the focussing helicoid. This, combined with the shear length of the lens, mean to need a clamp like this one to fix the lens to the helicoid. I got mine on eBay from a company based in Belarus called RAFCamera. Fortunately 62.5mm is a pretty standard diameter for lenses designed for 35mm cinema projectors, particularly from the Soviet Union, so once you have this adapter you should be able to use it with many different such lenses. My clamp has become permanently stuck to my M65 helicoid which is why the image shows the two items together!
M42 to M65 step-up ring
The next thing you need is a step-up ring to convert the camera end of your focussing helicoid to an M42 mount. I got mine second hand on eBay
Slim M42 to Sony E adapter.
This ultra slim M42 to Sony E adapter is designed specifically for attaching focusing helicoids to Sony mirrorless cameras. Head to Amazon or eBay to find a similar one.
The method for building this lens is reasonably simply as you really just have scree everything together. Begin my screwing your 62.5mm to M65 clamp into the lens end of your focussing helicoid. Then screw the M42 ro M65 step-up ring into the camera end. The screw on the ultra slim Sony E Mount to M42 adapter into the step up ring. The last thing to do is insert the camera end of the lens into the end of your completed adapter. The 62.5mm to M65 clap will come with an allen key to tighten some screws to keep your lens in place. The you're ready to mount your lens on your camera.
You can use your camera's manual focusing aids to focus just like with any other manual focus lens.
Notes on using your adapted projector lens
As I said at the top of the page my lens arrived in very poor condition, with the coating in particular being very decayed. This meant that the results were pretty awful! Fortunately I didn't spend very much money on it, and since it came from Ukraine I decided not to return it given then terrible event currently going on there. It's also worth bearing min mond that this is a very uncomfortable lens to use as it is so wide there isn't enough space for your fingers between the camera's hand grip and the helicoid.
But I still thought the results were interesting enough that I haven't entirely given up on this sort of lens. I will keep an eye out on eBay for one in better condition and then update this page if I find one.