Astro camera T2 (M42x0.75) to Canon EF lens adapter with 2" filter threads

thingiverse

I wanted a Canon to astro camera lens adapter that had internal 2" filter threads, so I made one from scratch. The adapter is 2 pieces threaded together to allow access to the filter threads. The Canon EF sensor spacing is 44mm, so I made two different lens adapter rings, one each for 17.5mm and 12.5mm cameras. The camera/filter piece is male M42x0.75 threaded to fit almost any astro camera on the market, or any t2/m42 type connection. The other side is threaded to fit the lens adapter piece, and also contains the female 2" filter threads (M48). You may have to mess around with you print settings, my first attempt came out about 0.5mm less than desired on all outer dimensions, so I changed my walls to print outside first to try and help fix it. Both pieces need supports since they have 90 degree overhangs. The lens rings should be printed with the camera lens clamps closer to the build plate to minimize the supports, and the other side of the clamps are sloped to bite into the lens clips. The other piece can be printed either side down, I've tried both ways, but I think having the M42 threads facing up makes a cleaner print. I made both pieces 0.1mm resolution so that the threads would match up as best as possible, and 0.1 is pretty much required for the fine m42 and m48 threads. I also printed both with the z seam lined up at the same point, and it makes a great guide for when it's fully tightened together (see the pictures). Mine are printed with the superhard carbon fiber polycarbonate off Amazon, but PETG should also work fine. I always use carbon fiber filaments though for astro camera parts so they're as strong as possible. Post printing can be a pain depending on how clean your threads come out. I normally go around them carefully with an exacto knife to clean the seam and any burrs. Then I carefully thread an extension into the M48 and M42 threads to clean them the rest of the way, just make sure it threads perfectly, or the plastic threads will be ruined. The lens clamps do not lock in like they would on the camera, so make sure it tightens securely, or even put tape on it to keep it together. Always test the strength of your build thoroughly since you'll be hanging potentially thousands of dollars on thin plastic threads! I am comfortable with this since I've been using the same filament and threads for months without issue now, but it would only take one weak layer to cause serious issues. Edit: After testing this on multiple lenses, I have found that shorter focal length lenses need to be closer to the sensor to reach infinity. I'm going to include a short version of lens ring to allow for any range of lens focal length and camera. Basically you'll just need to add the correct amount of spacers to reach focus. The short version should be about 5mm from the right spacing for a 17.5mm camera, and 10mm for a 12.5mm camera. With my 6-12mm fisheye lens I have to use my 0.5mm spacer to get it just right.