Quote:
Originally Posted by tlgerdes
Field flatness and illuminated imaging area would be the two key points.
Take a standard visual 8" Newt, most have a small secondary of around 50mm, whereas an imaging Newt will have a secondary of around 70mm or greater, creating a larger illumunated area for your CCD to minimise vignetting.
|
Hi,
if there is no vignetting with a visual ota and the 50mm secondary and the illuminated area is correct, by using a custom focuser (lower than a low profile) to achieve focus and without moving the primary, will a bigger secondary still be required?
in theory, this would not cause vignetting as the secondary would still cover the light cone?