Im trying to work out the full illumination circle of my Skywatcher 10" dobsonian to find the culprit of the vingetting (bigger secondary, bigger focuser, more efficient apperature to camera/focuser interface).
Im using Newt which is a raytrace program and tonight im going to use vernier callipers to get all the correct distances to give the exact ray trace.
Does anybody know a formula/method for calculating the illumination circle?
Your help will be apprciated.
Brendan
