What do imagers use to achieve adjustable back focus and sharp focus for the guide camera? (My guide camera is a ASI290mm mini cam). DO you take in account of any back focus on the guide camera? I believe the main camera light path is correct and I get sharp round stars.
Main camera light path = FR/FL with a back focus of 55 mm, (A) TOAG adapter (FR/FL to TOAG), (B) Orion TOAG, (C) 12 mm spacer, (D) ZWO EFW-7, (E) ASI1600 mm
A = 6.25 mm, B = 10.75 mm, C 12 mm, D= 20 mm, E = 6.5 mm (with 10 mm ring removed shoulder to sensor = 6.5 mm)
Light path (from FR/FL) = 6.25 + 10.75 + 12 + 20 + 6.5 mm = 55.5 mm for back focus spacing of main camera.
I measured the distance from (A) TOAG adapter (FR/FL to TOAG) to the prism and approx. 31 mm from the prism to the base of the of the guide camera platform
So I have approx. 41 mm and I need 13 to 14 mm additional spacing (adjustable desirable) for the back focus of the FR/FL.
DO you need to take in account of any back focus on the guide camera? I have seen to back focus specifications on the ASI290mm mini cam of 12.5mm and 8 mm. I am not sure what is correct.
Any help or suggestions would be greatly appreciated
