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I have been on this site for a few months and am posting images using a 70 mm scope with a reducer @ f4.9. My imaging experience is limited to about a year. I have a standard stock Canon 60D with a pixel size of 4.3uM. The seeing that I normally shoot my images is OK, not exceptional. I am using unguided rig and am working on putting together auto guiding. My thoughts are generated from the sampling of targets. For nebulae, this combination and sampling isn't such a bad thing as I can smooth the result and deemphasize the stars with processing. The issue is in star cloud images... with added luminance/noise reduction, comes the loss of detail. My camera has rather large pixels for the naturally wide field capability of my little scope, and thus I am always and forever under-sampling (pixel scale of ~2.61), especially when I reduce my effective focal length with a 0.8x reducer. This was a useful page to get a handle on this issue: https://astronomy.tools/calculators/ccd_suitability With OK seeing, I can walk the edge of acceptable resolution I think 🙂. Nontheless the other issue is that with no auto guiding, I am unable to use a computer to dither my lights. I guess these two realities conspire to require me to run the processing gauntlet... do I try for maximum sharpness (not likely the best plan - too much noise) or should I try to "smooth the result" thus taking me in a direction that may deviate from the raw subs eg, reality in representation? So, this is an ongoing obstacle, and something I am working on. I also am building my autoguiding capability (ASIAIR Pro, 290mm mini camera, 60 mm guide scope), and am waiting for ZWO to send me the camera. Perhaps I can improve my raw data, and I am excited to try it. Otherwise (by fiddling with the scope itself) I can try dropping the focal reducer, gaining back some focal length, and slightly improving my pixel scale. Or buy a camera with a chip using tiny pixels, like the 183. This has turned into a long-winded discussion, but I thought I might post these thoughts to stir some discussion about the problem. I welcome input... thank you for reading to the bottom. Ian |
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| Take lots of short subs and process with a drizzle. Unguided the drift between subs will act like an RA only dither. |
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| Thanks! |
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Hi Ian, I use the same telescope. Don't worry about your image scale.. you're just a little under-sampled. I've used mine with zwo asi1600 and asi533, the pixels are just a little bit smaller, my pixel scale is 2.33. It's not an issue. Your reducer is also a flattener.. without it your stars will look worse. I looked at some of your images.. pretty good considering the very short integration times. I noticed you are using a light pollution filter in bortle class 2/3. If you camera is a stock/unmodded camera, try without the light pollution filter.... and increase the total integration times if possible. |
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Hi James, Thanks for your kind comment, and also for your advice on the use of filters. I will definitely try removing them on moonless sessions. My camera is indeed stock... One of my tendencies is to jump to different targets (2 or more) in an evening. Not new to astro, but I am rather new to AP and I love to get a look at as many nebula as possible - those things that are very faint and colourless to naked eye observations. I am learning the importance of lots of data eg integration time, and I take your point well. 🙂 Best, Ian |
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Yes.. the color is what got me hooked! I can totally understand wanting to hit multiple targets in a single night.  |
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| Ian: I agree with James and David. For what its worth, I have never dithered and I rarely use filters or calibration frames but I take tons of short exposure frames. I can tell you with certainty, that guiding will be a game changer for you by giving you more control of your seeing conditions. Also I have found little success in trying multiple targets in a single session. I do not shoot much around a meridian flip either.mostly before or after. LOL. |
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James: Glad to see that I'm not alone, ha ha. |
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Ian: I agree with James and David. For what its worth, I have never dithered and I rarely use filters or calibration frames but I take tons of short exposure frames. I can tell you with certainty, that guiding will be a game changer for you by giving you more control of your seeing conditions. Also I have found little success in trying multiple targets in a single session. I do not shoot much around a meridian flip either.mostly before or after. LOL. Thanks wsg.. Good to know re: guiding - despite being another layer of complexity, I generally like sorting out these new challenges. I have my stuff on order too... come on ZWO (I need my 290mm mini to begin). 🙂 Best, Ian |
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To apply some of the advice..here is a sample of my "new" approach.. fewer filters and more lights. https://www.astrobin.com/hebprm/C/?nc=user Thanks, Ian |
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Warning: dither is the only way to avoid walking noise. Use it anytime you can. About your sampling, I agree with James: in Italy the mean seeing value is 2 arcseconds, so it won’t allow to catch details smaller than 2arcsec. In some areas is definitely better, but as you go in mountains zone which are more windy, turbolent and dark, things get worse. |
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Thanks Alessio, We have very few mountains to worry about in central Canada, but lots of access to relatively dark skies. I will look up how to implement dithering. 🙂 Ian |
