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Figure 21. M57, the Ring Nebula in Lyra. This is one of the author’s first autoguided

images obtained with his Compustar 14 and the autoguider described in this article using a

focal ratio of f/11. This image shows that despite the C14’s impressive focal length of 3900

mm, the Ring Nebula, measuring only 230 arcseconds, takes up only a small portion of the

image. The image was acquired with an unmodified Canon 20D DSLR as the imaging

camera, a Meade DSI as the guiding camera, and an off-axis guider. The image was taken

from Portland, Oregon, on 7/4/2010 at 8:14 UT. It is composed of 80 (yes, 80) 30-second

sub-exposures for a total exposure of 40 minutes at ISO 800. This is shown for comparison

to Figure 22.

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Celestron Compustar Bedienerhandbuch Seite 44