hy post=69080 wrote: SQM is an interesting number, but really I believe what thread is about is getting a good exposure values. My (gut feeling) belief on this is that if you're in the ballpark (e.g. if 240s was "optimal", 120s is probably in the ballpark, but not 10s), not saturating parts of the image you care about, stacking your subs for your final image, and have a modern camera with reasonably low read noise, then getting precise with exposure is overkill. Disclaimer--I've never won any image-of-the-day or top-pick awards


 

But we are talking about optimal exposure range. Based on SQM and our hardware we can calculate Sky Electron Rate in electrons/pixel/s
tools.sharpcap.co.uk
And then based on camera noise ratio we can calculate exposure time. Please analyze www.sharpcap.co.uk/sharpcap/features/smart-histogram.

Based on my two locations, focal ratio and gain, my optimal exposure time with 5% of background varies from 3s ! (urban with F/4 gain 300) to 300s (Bortle 3, F/10, gain 100)

Herę is gret explanation
youtu.be/3RH93UvP358?t=2038

Read More...