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Just did first light on Bode's galaxy with my brand new ASI585MC Pro. Came out pretty nice! I was using the recommended gain of 252 and I set the offset to 8. Seems like 180s exposures are over exposed, should I be reducing the gain and allowing more noise? I set exposure to 60 seconds to get a better histogram but was hoping to do 180 or 300s exposures. Any advice?? |
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I shoot with the 585MC, as well. Gain 252 almost always. What Bortle conditions are you shooting under? I shoot in B8, and generally do 30-second exposures and have decent results on Bode's with that. That said, I rarely go above 30s on any target because of the light pollution. Even with an L-Pro, the sky still starts to saturate out at around the minute mark. |
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I always shoot at 252 gain and 50 offset. At dark skies I use 180s and in the city skies mostly 60s subs. Here you can check my last image from this camera. I love it! https://www.astrobin.com/m9uocd/ Best, Mateusz |
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| While I still have yet to put much time on my 585 personally, I'd be pretty impressed if you're overexposed with that exposure length. You should be looking at the image in the linear with no stretch applied. Is the core of the galaxy visible, or blown out? Blowing out stars isn't all that big of a deal, as long as it's not too excessive. |
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Here is not stretched, just raw stack view. 180s subs gain252 |
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| Looks just fine to me. |
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I'm going to run some tests tonight with offset 50 and verify that it's overexposed at gain 252 and exposure 180s. I am in bortle 5-6 |
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This is the image I took last night with gain 252, offset 8 and 60second exposure https://www.astrobin.com/po4lzh/ |
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I'm going to run some tests tonight with offset 50 and verify that it's overexposed at gain 252 and exposure 180s. *** This might be too long for this sky quality. I would recommend 120s or even 90s *** |
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| Going to give M 13 a shot. |
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So M13 was pretty bright, 120second exposure was resulting in a completely white photo. I went with 30second exposures with this target: https://www.astrobin.com/0b7nec/ I guess the question is now, do I stick with very short exposures, or lower the gain? Will changing the offset help? |
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So M13 was pretty bright, 120second exposure was resulting in a completely white photo. *** Definitely 30s subs. Lower gain will not fix too saturated stars *** |
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Lowering the gain *does* reduce star saturation because the same number of electrons collected (i.e. the same amount of light) will result in a lower value read by the pixel. Saturation is simply the value hitting the maximum, so anything that makes it more difficult to achieve the maximum helps with saturation. Of course fainter signal suffers and read noise becomes more significant, otherwise we would be using only gain 0. It's a trade off. Based on the manufacturer's diagrams, lowering gain below 100 will give you better dynamic range than gain 252. And you will need 5 times as many electrons to reach the same signal intensity, which is important if your stars are blown. However, it would be a good idea first to make sure your stars are indeed saturated, because 30 seconds seems like awfully short time to manage and clip the tiny stars in the outskirts of M13. Maybe it is just your processing, especially BlurX if it is too aggressive, and of course the stretching done. Try reading out a few pixels on stars in the (unstretched) image after background removal. Does it say 65535 or whatever the maximum value is? If not, then they are not saturated. Proceed to stretching with MaskedStretch, leaving everything to default. You should be able to discern two star populations (blue and yellow). That's what you are aiming for, in the main. Cheers, Dimitris |
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Lowering the gain *does* reduce star saturation because the same number of electrons collected (i.e. the same amount of light) will result in a lower value read by the pixel. Saturation is simply the value hitting the maximum, so anything that makes it more difficult to achieve the maximum helps with saturation. Of course fainter signal suffers and read noise becomes more significant, otherwise we would be using only gain 0. It's a trade off. Thank you! Great advice! |
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Hey, has anyone figured out which offset is best for this camera? Best, Mateusz |
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Mateusz Bogucki: Cuiv the lazy geek's video came out to "8" but I am set at "3" now which is what ASCOM showed as default and it seems to work well. Maybe others can chime in with their experiences. |
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Mateusz Bogucki: Offset of 20 should be fine with gain 252 check the histogram and make sure your not clipping the data I think any lower than 15 then your likely to far to the left of histogram, I’m using 252g /off 30 , obviously if you use different gain then recheck your histogram so offset isn’t to far left . Dave |
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So update. I couldn’t do anything with offset to 3. In fact I was having trouble polar aligning because the stars were so weak. I am back to offset 8 for now but will test some higher settings. |
