For various reasons, I've been using ISO 1600 for most of my imaging. Long story short: not-so-great tracking limiting me to shorter exposures (maximum 30 seconds). As a result, my images are rather noisy, and it's a challenge to reduce that noise while retaining image details.
The short answer to this is probably "No kidding. That's why you should use a lower ISO." Sure, I've love to. At ISO 100, my Nikon D7000 produces fine images, limited mostly by what lens I'm using. And yes, I probably need a better mount.
I get that adding frames is intended to increase the signal-to-noise ratio. But how much effect does simply adding frames have on noise? Or is that primarily a function of increasing signal, and not so much at reducing noise? And will using a lower ISO actually reduce this noise?
By way of illustration, noise is somewhat reduced at higher frame counts, but not really that much:
Crop of a single frame of M31 at 30s, f/5.6, ISO 1600, 18-140mm zoom lens set at 140mm, brightness increased just to show noise:
30 frames at the same settings, Siril for stacking, photometric color calibration, and automatic histogram adjustment (no other modifications):
202 frames at the same settings, Siril for stacking, photometric color calibration, and automatic histogram adjustment (no other modifications):
I know these images are not terribly sharp, but that's more a function of using my less-than-premium zoom lens rather than a nicer fixed focal length. I guess I'm just curious as to whether this residual noise is to be expected at ISO 1600, and whether using lower ISO and/or more frames will actually reduce it.
Thanks for any insights!