Thanks Daniel! I'll see about picking up the Suitter book. I was outside last night, attempting to collimate the scope using a star. I'm not well practiced at collimating. I got CLOSE last night before some high clouds started rolling in. The alignment is still not perfect. Here is a photo. Threw the Nikon D800 on the back of the LX200GPS 12" after playing with the collimation (and just before the clouds rolled though). This shot was a quickie 3 second photo @ ISO6400 of the Orion Nebula. https://www.flickr.com/photos/22238456@N04/13051356465/ I'll keep working at it. If I can't get the collimation correct, the next time I bring the LX200 to a SPOC star party, I may request some collimating tips and tricks from you guys. I'm not interested in star testing the scope. Just collinating the scope as well as possible. Bruce Hugo ________________________________ Date: Sun, 9 Mar 2014 13:05:05 -0700 (PDT) From: daniel turner <outwest112@yahoo.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Subject: Re: [Utah-astronomy] Not enough backfocus Message-ID: <1394395505.95243.YahooMailNeo@web125001.mail.ne1.yahoo.com> Content-Type: text/plain; charset=iso-8859-1 Bruce: Now I see what this device is all about.? You don't need to come to focus with it.? The defocused image is a doughnut and you collimate by centering the hole in the doughnut.? I can't comment on the usefulness of the tool but a defocused view on a real star will do just as good.? The book by Harold Suitter that I mentioned is a classic on the physics of the amateur telescope (by a physicist no less).? And it is well worth the time spend reading it.? When you mention "star test" or artificial star, many (older) amateurs think in terms of the concepts in his book.? His main emphasis is on evaluating the figure of the parabolic Newtonian reflector mirror.? You can do this with an artificial star but you have to move it out to a distance of several hundred meters depending to the size and speed of the mirror.? Doing the test at a short distance will make the image appear as if the mirror has a nasty amount of spherical aberration.? That's why warning flags go up when you mention a test star at a short distance.? Many good mirrors have been called bad either by mistake, or as part of a ploy to sell you on a refiguring service.? As a rule then, don't let someone "test" your telescope for you.? It's a good bet that they don't know any more about the subject than you do and it's so easy to be oh so wrong.? As similar warning goes for collimation.? An adequately aligned telescope in the hands of a helpful but incompetent stranger can be thrown so far off that the evening's viewing is ruined. DT