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This could also very well be a vibration issue with a failing fan in your 1600 Good point Ara! |
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Hi Kapil, Using ASTAP software and the option CCD inspector, you can measure the tilt and off-axis abberation, by using one fits file, click ccd inspector and the software will report the tilt on your optical train. astap can be found here: https://www.hnsky.org/astap.htm this test may help you understand what might be wrong with your setup. I took your image and used the 'astap' image ccd inspector, and this is what ASTAP reported. It would be best to run it using a fits file.  If you defocus your stars, do you see a perfect doughnut or a circle within a circle or is the dark circle off-center? example of a defocus star where collimation is required...  For my setup, using a reducer, last year, my stars were egg-shaped but I discovered the sct backfocus distance was wrong. This year, I used ASTAP to 'tune' the sct. With my RASA, tilt is an issue, and I usually rotate the baader system/CCD (with ASTAP indicating lower tilt values) until the tilt is at a minimum. You could open up the fastar mirror and check that it has no tilt. Before you do that, read on how to open up the diagonal chamber (fastar). This tuning takes time, one month this year, and every year... hope this helps. Richard |
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Rich Sky: Hi Rich, thank you so much for taking time to help troubleshoot. I can definitely verify that the scope is collimated well. I have been checking it every night to doubly make sure. It could be bad backfocus as I have never really measured or checked it. I just usually moved on after I focused a center star. I need to do some thinking and tuning here anyway, if I want to go with OAG to eliminate other possible cause (flexsure). |
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I agree with what Tim has already suggested as a possible cause and solution. I will add one more thing though: This could also very well be a vibration issue with a failing fan in your 1600, which I experienced just a couple of months ago with my ASI294MC Pro. Thanks Ara. I will give this a try tonight and confirm. |
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Many of us have tried and failed to use a guidescope with a longer focal length main scope. Differential flexure of some kind always seems to creep back in and ruin some subs of 5 minutes or longer. You can spend a lot of time trying to minimize this, but in the end, using an OAG or ONAG or some other guiding technique that sees through the scope is the best solution. Be aware that using these devices makes it much harder to find guide stars, and I had to fit a rotator into my image gear in order to even have a chance on some objects that were not in the Milky Way, like galaxies. Frank |
