Tareq wrote in post #18495196
Talking about that M45 in this thread, so you have 140 frames for stacking, each frame is 1 second, that is translated into 2 minutes and 20 seconds, then what about a single frame or exposure that is 3 minutes or even 5 minutes? what if i take frames of about 10-15 and each frame is only 2 minutes? So if i have more frames to stack it will be better than a single frame same exposure long of the stacked ones?.
Quality of signal is important, so a longer exposure time will yield more signal than a shorter exposure time will. Stacking simply reduces random noise and keeps constant signal. But if your signal is already really weak, it's not going to get stronger, it's just not going be lost as noise. As the noise is reduced, the signal to the noise's ratio becomes more favorable to the signal.
You simply cannot get much signal from a 1 second exposure compared to a longer exposure (on the order of several minutes). There are extreme imagers who do capture 2~3 second exposures of feint galaxies, and stack them, but they're stacking on the order of several thousand images to achieve it, not just a few or even a hundred (and generally are using small sensor USB cameras, not dSLR's, and especially take advantage of monochrome sensors).
You will get far more out of a 2 minute exposure, 10~15 of them, than even 120 exposures of 1 second. Again, the number of images being stacked primarily reduces random noise. But to get better signal and more of it, you simply need to expose longer.
Bottom line: expose for as long as your system can tolerate. Get more higher quality signal. Get lots of them if you can. I'd rather have 30 x 3~4 minute exposures than 1,000 x 5 second exposures.
For example, here's a single 3 minute exposure at F6 and ISO 800. You can see the flame nebula pretty well on its own from just this one single non-processed non-stacked exposure (this is literally unprocessed beyond converting to JPG). You can see the feint outline of the Horse Head nebula too to the right of it. Just an outline really. And it's surrounded with dust other trails, but you can't really see those here from this single exposure.
Single exposure, 180 seconds, F6, ISO 800:
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Here's the stack of 37 x 180 seconds, or 111 minutes, just a little shy of two hours of exposure time with the histogram stretched and some minor processing:IMAGE LINK: https://flic.kr/p/QW4q47 FlameHorseHead_01232017
by Martin Wise
, on Flickr
And here's the same data after extensive processing to pull out all the data in the near-2-hours of signal that was captured (the dust primarily around the nebula that I wanted to extract). Because as always, there's rarely ever truly black space out there, with enough signal you'll find there's dust every where.IMAGE LINK: https://flic.kr/p/QBWuoz FlameHorseHead_ReProc_01232017
by Martin Wise
, on Flickr