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| I am doing a competition with 1 second exposures, and am still learning about the Gain settings. I typically run 100 as the recommended setting for my longer exposures. I somewhat understand if the gain is adjusted from 100, it impacts the dynamic range and read noise. But I am not sure what the setting should be on lower exposure times. Thanks for any suggestions/input. |
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| For one second, it should be the highest possible that gives you a meaningful reduction in read noise. I would say 350 to 400. |
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 Gain 100 (or some use 101) is where you have the most significant gain in reduction of read noise while preserving dynamic range and decent full well depth on the 533MC Pro. You could go higher in terms of gain, but you'll lose quite a bit of dynamic range and well depth, while not gaining much otherwise (presumably your SNR would increase), so it depends on what your goal for the competition ultimately is I guess! |
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| I typically run 102, but with exposures ranging from 180-300 seconds. 1 second is a challenging concept, and I did not know if the gain should be turned up with such short exposure lengths. |
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It should. Todd Tucker: It should. There is no way you will exhaust the available dynamic range with such a short exposure, while read noise is the dominant type of undesirable signal. I would actually be tempted to recommend cranking it up at the maximum value (450+) where you get minimum read noise with plenty of dynamic range available, but don't like how the sensor appears to behave above 400 with the RN actually rising somewhat just before that final drop. Best play it a little safer  |
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| I made an application in Excel which allows me to calculate the exposure times according to the Gain, the focal lengths and the diameter used, the size of the objects and the surface magnitude. I made some modifications in my formulas to give you the calculation for M 101 photographed with your Askar 120APO Focal Length 800mm. Result: We can do Lucky Imaging with an exposure of 1.3'' with a Gain of 500 Magnitude accessible 17 approximately. In these conditions, 40” of installation is required to reach magnitude 20. We find the parameters of long exposures with an exposure of 300'' with a Gain of 100 Magnitude accessible around 20. For a 10” exposure with a Gain of 100 Magnitude accessible around 17, this is the limit of Lucky Imaging. ForThe Pinwheel Galaxy M101 with your Askar 120APO Caméra ASI533[b] [/b][b] [/b][b] [/b] Exposures duration 120/800 : 108' Accessible Magnitude[b] [/b] Gain 20 19 18 17 50 711" 225" 71" 23" 100 299 " 95" 30" 9,5" 300 76" 24" 7,6" 2,4" 400 53" 17" 5,3" 1,7" 500 40 " 13" 4" 1,3" |
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| Very generous of you. Thank you so much!! |
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| I will be using my Rokinon 135mm @ f/4 with my ASI533MC @ 1" max exposures on targets ranging from a magnitude of 4.5 to 6. |
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Is the maths you used available somewhere ? Or the spreadsheet ? I'd like to see what it says for BigMak and Juniorburger. |
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Todd Tucker: Ah I see what you mean now. Yes, I think you could certainly crank it up like others have mentioned. |
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| Thanks to all for your input. I appreciate any advice, as I am still learning. |
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I did a few experiments at 1 second and 0.2 secs to see what was possible resolution-wise, since my rig is oversampled, ie so short that tracking and seeing would not be an issue. The results were interesting inasmuch as showing the extent that longer subs are degraded by these. Currently using subs between 30…300s at f/5 or f/12. What I’d really like to know is how long subs should run at a good dark site (Bortle 1 or 2). |
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| I redid the calculations for your Rokinon 135mm @ f/4[b] [/b] Regarding the apparent magnitude objective of 4.5 to 6, this means nothing because it is the surface magnitude that must be taken into account. For example :[b] [/b] For M 101 Visual magnitude: +7.9 / Surface magnitude: +14.8[b] [/b] For M 51 Visual magnitude: +8.4 – Surface magnitude: +12.9[b] [/b] For M31 Visual Magnitude: +3.4 / Surface Magnitude: +13.5[b] [/b] For M 42 Visual magnitude: +4 / Surface magnitude: +11[b] [/b] For M 45 Visual magnitude: +1.2 – Surface magnitude: +11[b] [/b] For M 13 Visual magnitude: +5.8 – Surface magnitude: +12[b] [/b] Two simple rules: 1- Multiply by 3.16 tps pose image to gain 1 magnitude more for equal gain and by 10 for 2 magnitudes[b] [/b][b] [/b] 2- Multiply by 1.32 image exposure tps to change a Gain from 500 to 400, and by 1.89 to change a Gain from 500 to 300, etc. ForThe Pinwheel Galaxy M101[i] [/i]with your Rokinon 135mm @J.F. Caméra ASI533 Exposures duration pour Rokinon 135mm @ f/4: 40' Accessible surface magnitude Gain 20 19 18 17 Exposures time / Frames " 100 3100” 980” 310” 98” 200 1300 " 412" 130" 41" 300 785" 248" 78" 25" 400 548" 173" 55" 17" 500 414 " 131" 41" 13" PS: The calculations in my spreadsheet were done for my Newton 150/600 Quattro and 254/1200 with the Nexus reducer of 0.75 and barlow x2- x3 x5. Given the complexity of the equations it is not transposable. PS bis: For the previous comment there is an error: the exposure time for your 120mm/800 is 108’ |
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| Thank you, again!!! |
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| Nick, I don't know BigMak or Juniorburger, but if your question concerns NGC 3628 Hamburger Galaxy the subs are very close to those displayed in my first comment for a 120/800 telescope. The calculations in my spreadsheet were done for my Newton 150/600 Quattro and 254/1200 with the Nexus reducer of 0.75 and barlow x2- x3 x5. Given the complexity of the equations it is not transposable. |
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Thanks... that table of values for M101 correlates with my own experience with Juniorburger (MN65, 165mm f/5). Primary limit here is sky background as my home site is Bortle 6-7, though occasionally travel to a much darker site. The relationship in your table between gain vs time vs magnitude is obvious, mathematically. |
