Re: [ATM] More on aperature stops

[Jeff Rowe <jroweapp@swbell.net>]

Dear Mike;

>I cool down my scopes a minimum of an hour before
>using and collimating. I use a laser collimator to
>collimate before every viewing.
>  
>
Two quick thoughts, Bryan Greer in his S&T article has shown the ill 
effects of heat rising off the face of ones mirror of only a few degrees 
difference. The addition of a small computer fan blowing across the face 
of your primary may be helpful. I have 2 big fans on the back, and a 
smaller fan blowing across the face of my 16. A night ago I set up and 
looked at Mars and it was not so good until I plugged the fans in for 1+ 
hours, then life got good. I used the whole mirror, and I'm glad I did.

Its been stated here before, just because a laser beam reflects back 
upon itself, it does not follow that a scope is collimated. Forget about 
the primary, tape a piece of paper right across the inside of your tube, 
right below your diagonal. Take a look.  Is the secondary square to the 
inside of the focus barrel, ( does your diagonal form a centered circle 
within  the barrel)?  Dont't touch the secondary once its centered. 
Remove the paper, can you see all of the primary? Adjust the primary 
until you can.  If your mirror is center dotted,  put a peepsight (35mm 
film container with a hole in its center) in your focuser.  Adjust your 
collimation screws on the back of your mirror till your dot is centered. 
Voila.

Jeff


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