ATM Re: Experiential versus Emperical cage height minimum

[tkrajci@san.osd.mil]

>From: Tom Lakovic <tlakovic@comcast.net>

>...I need help in determining my minimal 'pretty good' cage height and
>still have adequate baffling without the need for a velcro on extension. 
>Is
>there such a thing as a 'rule of thumb' minumum that does not require 
>stick
>on extensions in the field? 

Many variables at play...distance of focal plane from secondary mirror, 
desired size of fully illuminated field, etc.  See:
http://overton.tamu.edu/aset/krajci
specifically:
http://overton.tamu.edu/aset/krajci/dobsonian/dobsonian.htm
for some photos of a scope that has a small baffle disk, thanks to a 
baffle below the focuser and a 'not low profile' focal plane location.  
(Especially the bottom half of the web page.)  Baffle disk is about 8 
inches in diameter.

>Details: 2 ring design 15" ID, primary=13.1", stalk, stalk, vanes and
>secondary height 7",  2" focusser at the bottom ring.

Can you post diagrams, pictures, etc?  It gets lengthy and error prone to 
make long text posts on the topic of baffles.

See:
http://overton.tamu.edu/aset/krajci/scope-design.htm
..at the very bottom of this page is a diagram for one baffle situation.  
Yours is probably different, but a picture's worth a thousand words.

I hope this helps.

Tom Krajci
Tashkent, Uzbekistan