UlteriorModem wrote: ↑Thu Jun 18, 2020 4:57 pm
I dont buy it. There is no way you can collect as much depth of data with 100 x 30 second exposures vs 10 x 300 second exposures.
It has to do with the gain - sure, if you use the same gain you'd be absolutely correct (there are YouTube videos demonstrating this), but if you change the gain and especially in these newer
CMOS cameras you can push up the gain with little consequence (in terms of noises, etc.) then you can capture the same details. So if you ever do these experiments where you compare the two, you need to consider different gain. Still in the end even with a higher gain, I think you can get very close but it will not be the same unless you do MORE. If you do 100+ 30 second exposures (the + would depend on your conditions/environment, rig, and target) then you could match or even exceed the the 10x300 second exposures. You may argue that's not a fair comparison since the total exposure length changes but the people looking to do shorter exposures have some reason that might involve tracking/guiding/etc. so they may not have a choice but it is possible.
In the end, the correct exposure length/gain/other parametres is based on a combination of factors that includes your setup, your environment, and your target (which is related to the environment, I suppose but different places in the sky have different brightness and also whether you're doing NB or
RGB or
OSC). SharpCap has this "brain" histogram function that ostensibly do this for you - it takes you through a series of steps and figures out what the best sky limited exposure for that night would be that includes your setup and your environment but it doesn't always work though for some older cameras this has been figured out similar to the table posted by the OP so you can just look it up.
It's something I've been spending a lot of time figuring out and I still have little idea of how it all works but I do enough to know it can all be worked out in terms of math and it corresponds to real life pretty well provided we have people of the same expertise taking the images (the human factor obviously isn't taken into account).
--Ram
PS: Yes, the chart is camera specific and also different for different filters, etc. It's all about how much background light gets in relative to how much of your target you see and for modern
CMOS cameras it seems longer exposures aren't necessarily useful in places with a lot of light pollution especially.
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