Are watchmaker or mini lathes useful to make adapters and threaded rings for photography and optics tinkering?
The Proxxon doesn't look like it can cut threads so that won't help you in that area. As far as the other items you want to make it looks good. With practice you would probably get good results. I learned how to use a lathe in high school shop class and it's not hard. Some of the other much more expensive lathes can cut threads but with optional equipment.