A couple of new adapters

Astronomy gears are usually very complex and thus we need to have a wide range of adapters to fit them together. This time, I've two small stuffs:



1. PST etalon adapter improvement: thread is added so that the 1.25" visual back can now take a BF10 or a PST-BF5 visual back, the former one has larger aperture but it takes more back focus, the latter one has smaller aperture but it requires less back focus and it is in straight through configuration

2. Mini-Borg to NGF-S adapter: I used to connect my Mini-Borg with a #7508, a 2" -> SCT adapter, and then the NGF-S SCT thread adapter, now it's replaced by a single one with one side of m57p0.75 and the other side the interface for NGF-S. This makes the whole thing simpler, and thus stronger, lighter weight and also produce around 1cm more back focus

On my list, I still want a 2" -> Canon EOS adapter and a 1.25" -> SCT thread adapter.