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| I had the same problem with the Celestron OAG. Loved it, but once I needed a tilt adjuster, the OAG took up too much space so I had to remove it from the image train. |
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I hear the pain of oblong stars and I have the same problems with my EDGE HD8. However, I never thought to check the FR and see if that was the problem. I received some inexpensive shims from astrodymium which I hope will sort out my oblong star issues in parts of my image. I choose these since I'm limited with BF with my ASI1600, Celestron OAG and ZWO EFW. I'll report when I've tried them out. David |
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I've had a few clear nights with my Edge HD 8 working at both f10 and f7 using my ASI 6200 MM pro. I switched the scope to an iOptron GEM 28 from my CGEM II. I realize I wont get a flat field at f7 with the 6200 chip but I had it 'bolted' to the ZWO OAG and filter wheel and I just seemed like that was much firmer set up than the screw fit set up I had before. I used the standard distances prescribed by Celestron for the scope at f10 and f7. In both cases I was able to get round stars which I haven't with previous setups. I think what was key was the more robust EFW/OAG set up and much better guiding. While at it's limit the GEM28 achieved less than 1 arc second guiding which I was never getting with the CGEM, I was also much more careful with cable management! It was quite an exercise which ranged from wanting to throw the whole thing in the trash to being amazed when it suddenly all came together. Bottom line there is a lot going on at 2020 or 1400 mm focal length and I seem to have found a solution that works for me especially given that I BIN 2x2 even at f7 which is more than enough resolution for my backyard. The difference in photon capture between f10 and f7 is very noticeable I'd say more than the the 2x math would lead one to believe, especially in Ha, perhaps it's a light pollution effect. So I'm planning to stick with f7 and just crop the image, the useable FOV at f7 and f10 is about the same. CS John |
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I had a similar problem to you with smaller stars being oblong. It was caused by vibration from the fan in the ASI1600mm. The stars remain oblong in short exposures of 5 seconds. You can check if this is the problem by comparing images with cooling off and on, this should turn off or lower the fan speed. I replaced the stock 40mm fan with a Noctua fan. |
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| Our adjustment is done for now. QHYCCD OAG-M plus some adapters has been installed (backfocus distance is correct), colimated and focused but not tested .... yet. We will report! |
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Hi All, following up on this topic i would like to report the issue seems to be resolved. Latest picture https://www.astrobin.com/x8jjuk/ shows round-ish stars. As described earlier following steps have been done: - Installation new / other / slimer OAG (QHYOAG-M) - Fiddling around with adapters to achieve correct backfocus (+- 0.5mm) - waiting for 2 months for a clear night to achieve correct focus and collimation (Metaguide) We would like to thank you all for your help. Cheers Jacob |
