Flaming star nebula

[micheleorsini]

Hi Startools friends!
here is another image! flaming star nebula

http://www.astrobin.com/275905/?nc=user

as I wrote on astrobin: the image needed more frames, fortunately the subject is incredibly beautiful!

If you noticed the unusual set of frames, here the explanation: I wanted to test which ISO is best for my camera and I planned to make 2 or 3 nights changing ISO to see which one got better results. Unfortunately we had clouds for all nights except for the first one, so my tests had to be stopped.

Here is the rationale of my ISO explorations

1. I did my homework reading all possible articles on the subject and coming to the conclusion that the right ISO for my camera is 800 or 1600 ISO
2. but I'm living in a quite polluted city so this means that I have to use single frame exposures of 1 minute or 2 minutes (at 800ISO)
3. somewhere I read that the lenght of the single frame is important too: you are giving more time to the faintest parts of your DSO to send photons to you. If you don't have signal, it is useless to average tons of frames, right?
4. so I wanted to test how much I loose in noise picking a lower ISO

ok, the temporary conclusion is that there is no significative difference between 400ISO, 800ISO and 1600ISO: after stacking and a quick post processing the image produced with 40 minutes of frames are almost of the same quality.
Most probably the explanation is that the real problem of my environment is light pollution and everything else is negligible. So, until further notice, I'll stick with 400

(please note that I did a similar test this summer with the veil which is much fainter and it seemed to me that the 400ISO stack was slightly better)

cheers

Michele

[Rkonrad]

Beautiful image.

My understanding is that lower iso produces more read noise but more dynamic range. You're image has a relatively low dynamic range. So technically you have more noise to deal with at 400 compared to 1600. I'm not sure how much though.

Richard

[micheleorsini]

I agree with you Richard and I'm considering adopting a double strategy using lower ISO for high dynamic range images only
Still, doubt persists: how much time is "enough" for a frame to have faintest detail photons reaching the sensor?