[ATM] secondary mirror help

[Oakley <oakley@spymac.com>]

Hi all,
   I'm well into my first telescope building project, and I'm a little
stumped on the secondary mirror.

   I've done a lot of research into this, and I'm just hoping I could
get some people to verify that I'm not screwing this up! I'm using an:
- 8" f/6 mirror
- 10" diameter tube
- focuser with a racked in height of 2.69" and a focus travel of 1.5".

What I've come up from reading websites is:

Location of secondary mirror = 48 - 10"/2 - 2.69 - fudge factor
Ignoring the tube thickness (for now) and setting the fudge factor to
.25"(is that good?????) gives a value of 40" from the primary mirror

Thus the secondary mirror size should be (48"-40")/48" * 8" = 1.33"
To be safe I'd get the next largest size (Orion has a 1.5")

My Questions are:

-Is this mirror the right size (i.e. will I not lose light, and not
noticeably lose contrast)?

-Is this mirror in the right place? My tube is only 48" long, will ~6"
after the secondary mirror be sufficient? Will I be able to focus all 
eyepieces?

I'd really appreciate anyone who could tell me if I'm forgetting
anything, I'd hate to do all the drilling and attaching and then find
out I messed up!

Thanks,
   Phil
ps. any other suggests are more than welcome!

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