[AZ-Observing] [Fwd: Focusing input requested]

The method I use that works very well is to block the aperture with 
something (cardboard works well) with a width around half the diameter 
of the telescope's aperture all the way across and through the center of 
the aperture. When the scope is not in focus, you'll see two images 
similar to a range finder camera. When the two images combine into one, 
the scope is in good focus. Do this on a bright star near the area of 
sky you want to photograph and then compose your shot.

I use this method with my Canon EOS 20D and it works great. I also use a 
magnifying right angle finder on the camera's eyepiece to make it easier 
to see.

Rick Scott



-------- Original Message --------
Subject:        [AZ-Observing] Focusing input requested
Date:   Tue, 26 Feb 2008 4:15 PM
From:   Bob Christ <bchrist@xxxxxxxxxxxxxx>
Reply-To:       az-observing@xxxxxxxxxxxxx
To:     az-observing@xxxxxxxxxxxxx



Greetings all, some time ago I read an article (don't recall the 
reference) that addressed the use of diffraction spikes as a means to 
achieve a higher level of focus versus when astroimaging versus using a 
Hartman mask. The approach was touted as being easier and much more 
accurate. String or some other thin material, positioned to bisect the 
objective lens, creates the spike effect. When the width of the spikes 
has been minimized - excellent focus has been achieved. Has anyone used 
this technique? Is a single "string" used, or two at 90° apart? And, 
what is the thinness/thickness of material to use? Guidance will be
much appreciated.

Thanks,

Bob Christ



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