Large rack and pinion focuser for a large telescope and adapter for mounting various optics on an equatorial mount.
That’s great, I love it. Focusers are so expensive too.
I needed more travel than the commercial focusers provide. It is a 6" refractor. I drop the tube size down to 4" and that is what I designed the focuser for. It provides a rough focus and I still have the commercial focuser at the end of the 4" tube to provide fine focus.