[ATM] Secondary Cage Calculations (formula from Kriege + Berry's book)

[David Weinshenker <daze39@earthlink.net>]

Richard <cnc at cncservo.co.uk> wrote:

> Hi David,
> Sunday, October 7, 2007, 6:13:49 AM, you wrote:
> DW> ring ID = aperture + 1% of focal length

> Without knowing the focal ratio and the design field of view that
> statement is meaningless (like a lot of "rules of thumb")

Kriege + Berry are assuming a total angular field of view of 1/2 degree 
(i.e., +/- 1/4 degree from on-axis): thus they calculated the the extra 
diameter (for any aperture) required for this as: 

 sin (1/2 deg.) times the focal length 

and then rounded sin (1/2 deg.) = .00873 up to .01 (1%) 
for convenience  and to add a little extra margin. 

(Ref.: D. Kriege + R. Berry, "The Dobsonian Telescope", p.153-155)

-dave w
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