[Ukastronomer (Jeremy)]

Originally Posted by Atmos

You are pretty much right there, binoviewers and refractors don’t mix well with 2” diagonals.
Even with a 1.25” diagonal and short threaded components you are likely to need a Glass Path Compensator (GPC) which is a small threaded barlow to increase the back focus to allow a refractor to come into focus.

With my 4” refractor I used a 1.7x GPC which allows another 35mm of back focus from memory, a 1.25” diagonal with all threaded connections.

Both diagonals and binoviewers consume a lot of back focus.

Thanks so I am not alone, 1.25 does work but 2" is useless, thanks all