Coma corrector, auto-guider & M71

By the time I had acquired a DSLR camera and got my system capable of taking a half decent image the globular cluster M13 had gone too far over to attempt an image in a dark sky so the next cluster worth trying would be M71. By now I had converted my old 1.1/4"rack & pinion focuser to a 2" Crayford so that I could use the Baader coma corrector I had recently purchased. Expecting to see an immediate improvement in uniform star images across the field with the coma corrector I was disappointed when the first trial images looked terrible with distortions all over the field. Some research on the web indicated that the cause was likely to be poor collimation that apparently is super critical when using a corrector. An evening spent on achieving good collimation resulted in a massive improvement. At this stage the auto-guider was getting its first trials. This too was initially disappointing and my immediate reaction was that a lot of time had been spent on something that was never going to work properly. Once again the internet came to the rescue when I found a forum that led me in the right direction when it suggested I balance the scope biased to the east and run the RA drive slower than sidereal rate to force the guider to work in one direction only. This worked like a charm and the situation suddenly looked much brighter. It wasn't perfect but I was tempted to give it a try on M71. The resulting image (Canon 450D iso 400 & PHD guiding software on 7/11/08) is from 12x 100 second exposures (images only) in Deep Sky Stacker and CS2. (click on image for larger version)

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