Looking for some feedback on this...
I have a 12" dob (F/4.9) with a 2.75" secondary and a 2" focuser. The Newt program indicates there is vignetting at the focuser of the 75% ray. The diameter of the 75% illuminated area is 1.8304 inches.
If my lowest power eyepiece (Nagler 26mm) has a field stop of 35mm (1.3774 inches) which is half an inch smaller than the 75% zone. So is the vignetting really an issue? It seems like the field would be illuminated by the 100% and 75% rays and the vignetting is occuring outside the field.
Lastly, if I change the secondary to 2.6" the vignetting goes away but the 100% zone gets smaller. I'm not sure if the tradesoff are worth it. The central obstruction only changes from 23% to 22% and I am not sure I would see a difference.
Thoughts?
Thanks,
Mark
I have a 12" dob (F/4.9) with a 2.75" secondary and a 2" focuser. The Newt program indicates there is vignetting at the focuser of the 75% ray. The diameter of the 75% illuminated area is 1.8304 inches.
If my lowest power eyepiece (Nagler 26mm) has a field stop of 35mm (1.3774 inches) which is half an inch smaller than the 75% zone. So is the vignetting really an issue? It seems like the field would be illuminated by the 100% and 75% rays and the vignetting is occuring outside the field.
Lastly, if I change the secondary to 2.6" the vignetting goes away but the 100% zone gets smaller. I'm not sure if the tradesoff are worth it. The central obstruction only changes from 23% to 22% and I am not sure I would see a difference.
Thoughts?
Thanks,
Mark