Re: [ATM] what is strelh ratio and how do I mount the spider

[Mark Cowan <toolontop@yahoo.com>]

David, one excellent way to figure this out is to draw
a scale diagram - decide how much of the sky you want
fully illuminated at focus (say 1 degree, two moons
worth), imagine a circle with the radius of your
mirror, and note that 1 degree is 2*100*pi/360 or 1.7"
across at the focus of your mirror.

Draw out a truncated cone, 1.7" wide at the focal
plane, 20" wide at the mirror, and 100" along the
sides.  Measure where the focus plane (eyepiece field
stop) will be when you mount the focuser on the tube
(or estimate it), add in half the tube diameter.  Go
this far down your drawing (say 13.5" as a guess) and
then you can measure the size of diagonal you need. 
Fold the drawing at this point and now you can measure
all the other positions you're wondering about.

Mark Cowan
Salem, OR

--- David  Williams <dwilliams1128@earthlink.net>
wrote:> My question is this:  Given that the sonotube
is 8
> feet, 3 inches long and the focal length of the
> primary mirror is 100 inches, where should I place
> the eyepiece holder (focuser), spider, and primary
> mirror mount?
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 



		
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