[morls (Stephen)]

Hi,

I'm starting to think further about my 12" project, and have got to the point of looking at the secondary mirror and focuser. My primary is a GSO 12", which is currently being recoated. The GSO website lists the aperture as 304mm, which comes out as 11.97" and the focal length as 1500, which makes it an f4.93.

My main interest for this scope is deep sky, not planetary.

Using "Newt for the Web", I'm trying to find the best size for the secondary. I want to get a high quality mirror, so I'm looking at Antares Optics. It seems there are 2 options - 2.14" and 2.6". Ideally I'd like to go somewhere in the middle, but anyway...

If I go for the 2.6" (66mm), and a low-profile focuser, I get the following:
22% obstruction
Angular FOV for 100% illuminated area = 0.794º. Diameter = 20.66mm
Angular FOV for 75% illuminated are = 1.7176º. Diameter = 44.7mm

If I go for 2.14" (54.4mm):
18% obstruction
Angular FOV for 100% illuminated area = 0.2594º. Diameter = 6.75 mm
Angular FOV for 75% illuminated are = 1.2258º. Diameter = 31.9mm

So, I'm thinking the 2.6" is the better option.

What I'm wondering is:

If I have a large 100% illuminated field, does this mean I am 'wasting light' if it exceeds the field stop of my largest eyepiece?

As always, any advice would be greatly appreciated.

Cheers

Stephen