[AZ-Observing] [Fwd: Focusing input requested]
- From: Rick SCOTT <rmscott@xxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Tue, 26 Feb 2008 17:21:26 -0700
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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