Over the last few years, I've bought adapters for my Fuji X-series cameras that let me mount Leica, Nikon, Hasselblad, etc. lenses on them. This interests me for a few reasons: 1) instantly determine when I buy a used lens on eBay how good that copy is, without have to wait to develop film which introduces certain variables, 2) compare different models/copies of lenses for that brand of camera to see which is best and 3) compare the different look you get with classic film camera lenses to digital .
Unfortunately, there haven't been any adapters for Argus C3 lenses as manufacturers don't see it as a big enough market. So I decided to make my own for $31. Here's the process for Fuji X mount in case you want to try it. You could do something similar for Sony, Micro 4/3 or other mirrorless camera systems. Mirrorless cameras work best because they have a flange to sensor distance that is shorter than any film camera (even the Pentax Auto 110). Therefore it's a matter of making an adapter that extends from the mirrorless mount a sufficient distance to match the lens flange to focal plane distance of your film camera system.
First you need something that has the mount for your mirrorless system. I bought a cheap ($18) set of extension tubes for Fuji X mount. Extension tubes are cool because they give you several sections of differing lengths so you have options to find the one that works best for your lens.
Then you need to have something to mount your film lens to, in this case, the Argus C3 screw mount which is unfortunately, unique in the world with its 33mm thread. My solution was to use an Argus lens cap and drill out the back so it is mainly just the threads. No need to drill completely everything out, just got most of it with a series of 1/2 inch twist drills, then a rounded file.
Then you need to mate the extension tube with the lens cap. In my case, the Fotodiox brand Fuji extension tubes I bought use a regular 52mm filter thread to screw the various sections together. Since the Argus C3 lens cap is about 36mm in diameter, I used 52mm-43mm and 43mm-37mm step down rings. The last 1 mm difference in diameter was accomplished by wrapping blue masking tape twice around the outside of the lens cap. That is just enough to make up the size difference and gives some grip to screw the taped lens cap flush into the 37mm step down.
Then it was just a matter of getting the right overall length for the entire assembly. I found the 7mm extension tube was a bit short and the 14mm one was too long. So I used the 7mm extension tube + a 52mm UV filter to give me an extra 4-5mm of length. So altogether, the extension tube Fuji mount + 7mm extension tube + UV filter + the two step down rings give about 24mm of total length which matches the difference between the C3's 41.9mm flange to focal plane distance and the Fuji's 17.7mm flange to sensor distance.
Here is a test shot taken with the 100mm Sandmar C3 lens. Quite good quality taken at f/8 on a sunny day.
Note the X-Pro1 is APS-C sensor, so the lens acts like one that is 1.5x the nominal focal length of the lens.