Oh I see, because I’ve always had this thinking that longer subs = better (especially for narrowband). My scope isn’t exactly a fast one, what is your usual set-up May I ask? I was wondering if one or Two f-stop differences will significantly impact the required exposure time
Faster systems require less total imaging time to achieve the same signal to noise ratio. It's roughly the same as conventional photography, one f stop requires half the total time to achieve a similar result. Because, per pixel, you've acquired more photons per unit time. Obviously pixel size also plays, like much in AP of DSOs, this is not simple.
This is why I purchased a C8 RASA, F2. That's not cost free, F2 imaging can be challenging in more than one way. But it has its points. <smile>
I also image at F4.8, F5.8, and F7. With cameras with different pixel sizes. I adjust my total imaging time goal accordingly.
More longer exposures reduces the impact of read noise, at the cost of reduced dynamic range. It's a balancing act, not easily explained in a short post here.
It _is_ well explained in this book. It takes several pages, with graphics.
But the bottom line remains. Once you're in the ballpark for subexposure times (and narrowband changes the playing field <smile>), total imaging time is _far_ more important. It's all too common for beginners to skimp on that.
Edited by bobzeq25, 21 November 2019 - 10:28 PM.