[ATM] Follow-up on focuser protrusion

[John Lynch <john_p_lynch2004@yahoo.com>]

To the ATM listserv:
 
I went back and redesigned the layout of my 8" f/6.25 telescope specifications,
and changed the image plane location to approximately 0.935" above the fully racked
in position using the JMI DX2.  This gives me a 100% illumination diameter of 0.76" 
and a 75% illuminaton diameter of 1.34".  This leaves me with about 1/8th inch outward margin for the shorter focal length eyepieces, which I think is acceptable if I'm careful in the layout and leave some adjustment in the mirror cell just in case.  The longer focal length eyepieces focus closer in without drawtube protrusion with the exception of one, and that one (UO 25mm Konig) is a little less than 1/16th of an inch into the light cone. 
I think this is pretty acceptable.  
 
My assessment is based on calculating the true field-of-view for each eyepiece and 
using the distance between the beveled mirror's edge and the inside of the telescope tube to project the gap between the edge of the light cone at the bottom of the focuser drawtube when the eyepieces are focused.  All theoretical at this point and probably somewhat academic.
 
Thanks for the advice that you all gave previously.
 
Regards,
 
John Lynch

		
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