[ATM] design question

["Kevin Williams" <kwilliams6176@verizon.net>]

I have built a 6" f5

I calculated the distance from primary to secondary based on a formula given
in Richard berry's  book

back of mirror location  = focal length - (1/2 tube diameter )- (height of
focuser(racked in)) - (1" for travel in focuser ) - (mirror thickness)

x = 30 - 7.75/2 - 2 - 1 - .625
x=22.5

so I cut the hole for the focuser,  mounted the secondary mirror, then
mounted the primary mirror

when I used the scope to look at the stars, I could not focus

the scope has a 2" focuser, and I use an adapter to use my 1 1/4 eyepieces,
I took off the adapter, and moved the eyepiece into the hole by holding it,
and I could focus, I estimate I had to hold the eyepiece 1/2" lower then the
focuser top (fully racked in) get it to focus

2 questions
what did I do wrong?
how much and which way do I need to move the  primary mirror? or something
else?

thanks
Kevin



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