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I am tring my first galaxy tonight, I only have a Samyang 135mm so it's quite small but it's gonna be fun anyway, an a good experience. Here's a preview from the Asiair. It's 300 seconds with an Optolong L-Pro. The core looks quite bright to me, I wonder if it will be burned when I stack 4 or 5 hours of this. Should I take shorter exposures ? Like maybe 120 seconds or even less ? |
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Can you provide a bit more info? Camera type, gain, Sky SQM (Bortle), etc. Are you shooting at F2? I would say 120 sec (or lower) at very low gain would be more than enough for that Focal Length but other factors need to be considered too.. |
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Eric, I typically image with 60 seconds for LRGB and 5 minutes for Narrowband. As you can tell, I image with a mono camera. I assume it would be similar for OSC. I also image from a Bortle 7-8 location. |
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| I should have given more details. It’s a cooled osc, shooting at gain 100, under bortle 6 sky at f2.8 |
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I would go by the information displayed on the histogram. Ive had success keeping the data 1/4 to 1/3 in from the left of the graph. J |
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Éric, moi aussi, mais en mono. Durant l'hiver, je ne met pas de refroidissement - la caméra ne peut pas atteindre -10°C quand il fait déjà -20°C dehors.... D'habitude je prends mes images à f/8. L'instrument le plus vite que j'ai est un Newtonian à f/4. Mon gain est 139 pour ma caméra mono. Comme j'ai dit, 60 secondes pour LRGB et 5 minutes pour NB. C'a me donne des assez bons résultats. J'ai moins de bruit de fonds de cette façon. Même après plusieurs années, j'en apprends encore! |
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| Purely depends on the focal length- At 2032mm like I shoot on, I take 5-10 minute exposures- minimum. On lower focal length (and quicker systems) I take only 1-5m exposures at a maximum. |
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| Running at 1 minute, I figured I should stick to that since there is a little wind, not much, but I couldn't get guiding to start this time, would not calibrate and I did not feel like losing time on this. |
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| Probably be better off at 30 seconds or less even maybe at f/2.8 at 135mm, 60 seconds would be about my max with my Sammy 125 under Bortle 3. With a dual narrow band I’ll go upto 120 seconds. |
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If it's not saturated in a sub, it won't saturate in a stack, right? Stacking averages out signal which stays in the same place in the star field. It doesn't intensify it. Stacking cancels out noise that moves around randomly. So if a galaxy core is 80% of full well in a sub, it's 80% in the stack. That's how I understand it. (I'm no mathematician. D'Oh) You want the sum of sky background and bright objects below 90% of saturation. Your 5min sub doesn't look blown out so maybe you could go to 8 min if you want more faint detail. But I think stacking twice as many 4 minute subs is almost the same end result. Just more work. It's the stretching after the stacking that makes faint objects bright. if you stretch a sub (before cancelling out noise) you amplify the noise more than the signal. |
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Éric, look at your histogram as you take the picture. If the peak of the histogram is well separated from the black point (left side), then it is enough to process. |
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Simply look at the linear image. Are the core details blown? No? Then you're good. |
