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Generally speaking, I personally shoot at iso800 if my exposures are in the 10 min range. ISO1600 if I take 5 min long exposures. I usually use stars as reference. Stating the obvious, if stars are overexposed I lower the ISO. I use a modified Canon SL2. How about you, guys?  |
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| I shoot at 2000 ASA for 2 mins with Sony A7III full frame. |
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A camera like that probably has an excellent ISO capability. Have you tried shooting 5 minutes or even 10 minutes exposures using low ISO for increased dynamic range? |
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| I have a Canon EOS Ra and I typically use 800 ISO. I expose from between 4 min - 7 min typically (depending on my f/value on my scope and how my histogram looks). I also shots from a bortle 8 zone and use filters like the L-eNhanced. If I am shooting filterless, my exposures are between 1-2 min and I will experiment between 400 ISO and 800 ISO. |
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You can do an experiment and find out yourself. For example, the attached images were taken (by a friend of mine) with Canon EOS 6D. All have exposure time of 30 second. Taken very close in time with identical optics. The image brightness was adjusted in Adobe Camera Raw to be the same. In short, every thing is identical except for ISO setting. This clearly tells you what ISO to use on this camera. Alternatively, you can look at the read noise curve on this page: https://www.photonstophotos.net/Charts/RN_e.htm Use the ISO with sufficiently low (but not necessarily the absolutely lowest) read noise.  |
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How does this balance with the drop in dynamic range as you increase the ISO? For my 5D Mark IV, the banding issue is another factor..... It's most pronounced at ISO 800, but for the most part gone at 2000 and higher. Cheers, Scott |
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| Dynamical range is a very very unimportant issue in deep-sky astrophotography. The key is always to find against all kinds of noise. Once you stack enough frames, the stacked DR becomes very high. |
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When imaging a faint object, or an object with a bright core and fainter outer areas, doesn't an increased dynamic range help with getting long enough exposures/high enough ISO for the object while not blowing out the stars or core? I realize taking images with different exoposures/ISO's and combining them using HDR also works in these situations. Cheers, Scott |
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Alessandro Cernuzzi: In short the answer is no as I was happy with 2 mins exposure and 2000ASA. Mind you for the core of M31 I probably should have gone for a very low ISO with more dynamic range to stop the trapezium blowing out. Moorefam |
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Scott Badger: Such extremely bright nebula cores are rare, they shouldn't be the priority when you are to establish a baseline workflow. When you really encounter such bright cores, just take a few additional shots at reduced exposure time. In my experience, only a handful of objects have such bright cores (M31, M42, M8, and a few small globular clusters). I don't always image such bright targets, and when I do, spending a few more minutes to take short exposures on their core isn't a problem. On the other hand, if you don't prioritize noise properties in your exposure strategy, you can be wasting hours of time every night. You can end up with spending 4 hours on a target but only reach a depth that's equivalent to just one hour of optimized exposure. Bright core vs. faint nebulas, which one is more important? I think the answer should be very obvious. |
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Wei-Hao Wang: I'll give you that.... For me, somewhat moot anyhow since I'll trade some dynamic range to not have the banding issue.Cheers, Scott |
