Telescope Adapter (Prime Focus) for 1.25" Eyepieces and Micro Four Thirds Mirrorless Camera

I had developed an adapter to attach my Olympus camera to my Meade reflecting telescope and shared it on Thingiverse. It worked, but a user noted that it would attach more securely to the camera if the entire Micro Four Thirds bayonet connector was used. The mechanism of the MFT camera needs holes in the outer parts for the pin to latch into. I had reduced it to just the interior part, mainly to get the camera closer to the scope so it would focus properly.

The eyepieces that came with the telescope (the two in front) were the 0.965" tube size and included not-so-great lenses. I learned that better eyepieces were available, and not too expensive. Look how much bigger the lenses are on the two in the back! But they have a 1.25" tube. To use those I would need to get a different focuser adapter from Meade, or design and print one. To switch from viewing to photographing I would need to swap the focuser adapters, which I really don't want to do. So I decided to design 1.25" focuser adapter for the new eyepieces, and redo the camera adapter to use that size and to latch correctly. The files are all available on Thingiverse.

I've had some experience with printing very fine parts with a 0.15mm nozzle and very small layer height, so I though I might be able to print the MFT camera adapter accurately enough for the latch to work. I took another look at the MFT file I had downloaded from Salvaged Circuitry and figured out how to lower it. I also took careful measurements of the new eyepieces and shortened the focuser part, so the eyepieces and camera would be at the right focus distance to work. So this project ended up as a total redesign.

I was able to measure the telescope focuser threads with a thread gauge. The screws I used are a common size with National Coarse threads. Neither of these thread sizes were available in Fusion 360's thread library, so I had to create custom threads using the Coil function. They all fit great.

The tricky part is that if printed normally, both the focuser adapter and the camera adapter would need to have overhangs, and I really did not want supports roughening up the surfaces. So I figured out how to design each of these adapters in two parts that I could glue together. This actually worked very well, and enabled me to prototype and fine-tune each of the four parts separately, reducing waste.

Here is the part that screws onto the telescope focuser. The blue and gray parts are printed separately, so no overhang occurs. The screw holes with threads print horizontally but are small enough that no sag occurs and no support is needed. The big gray part is printed as shown, so its flange and threads do not experience overhang. These two overlap a bit and are glued together as shown.

Here is the part that attaches to the camera bayonet mount. The part shown in blue prints upright as shown; there's a little flange at the bottom for gluing that's hard to see here. The gray part is printed upside-down, and the little tabs do not stick out enough to need supports. These two are glued together at the flange as shown.

The telescope part accepts an eyepiece or the camera part, and there are thumbscrews to tighten them in place. I've done some basic testing with the telescope, and the assembly is short enough that the focuser has enough travel to achieve focus.