I've always thought when comparing a obstructed telescope to a unobstructed telescope you
simply subtract the the obstruction from the obstructed telescope and you are left with the equivalent
A example being a C5:
5 inch aperture, minus it's 2 inch obstruction, leaves you with a 3 inch refractor.
And I thought the equivalency is in contrast, the resolution, the ability to see detail, will remain unchanged
meaning the C5 will resolve as a 5 inch aperture.
If you search for this information you get overwhelmed with differing opinions.
The reason I ask is because I really like my C5, but if I had to choose between it and a 3 inch f/15 I think I'd
go with the 3 inch refractor. But I might be more inclined to go with the C5 if it's truly going to perform as
a 5 inch on fine detail. I would rather have the aperture and not need it, than need it and not have it, but I
prefer driving the 3 inch f/15 refractor.
Comparing in the field can show a difference with certain observations like planetary detail and globular
clusters is where I see the C5 move out ahead of the 3 inch refractor, but otherwise it can be difficult to
tell the two apart.
Edited by clamchip, 04 December 2018 - 12:58 PM.