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Re: Picking the correct exposure for Deep Sky

Posted: Sun Feb 16, 2020 3:43 pm
Hi,

Yes, you're welcome to translate this content and share it. I would be very grateful if you could make sure that your translated version includes a link to the original content and credits me as the author.

Thanks, Robin

Re: Picking the correct exposure for Deep Sky

Posted: Mon Feb 17, 2020 1:10 am
Thank you very much Dr Robin!
Sure I will include a link to this thread and credit you as the author.
Thank you again!

Re: Picking the correct exposure for Deep Sky

Posted: Sun Mar 15, 2020 9:36 pm
Hi Robin,

I have been a user for 2 years and I found your noise analysis (previous posts) helpful and the March 9, 2019 video. I would like to see more of the math behind the calculations from the table in the video.

I run the sensor analysis and divide Full Well Depth by Read Noise and usually pick the point where the sensor changes gain amplifiers. What I find when discussing with individuals is 1) too long of exposures with an outside source (airplane lights, satellites, tracking issues) causing them to unwanted artifacts or 2) too much gain (poor SNR, over exposed), because the ability to see an image in real time exciting.

Equipment:
RASA 11" f/2.2
ZWO 6200 color (Read noise 1.53)
Optolong L-enhanced filter (maybe medium band filter)
Typical settings gain 100 and exposure time 30 to 120sec depending on object

I usually do not image for fixed time, but until I see a "smooth" histogram in front of the major peak and low ripple in the end of the histogram. My judgement based on observing the histogram develop.

My question is calculating the optimum number (10% or 5% noise) frames to stack?

thanks,
Mark

Re: Picking the correct exposure for Deep Sky

Posted: Sun Mar 15, 2020 9:57 pm
Hi Mark,

I think you can still use the calculation results even though you don't image for a fixed time – the calculations are trying to optimise to give you the best possible output image in a certain amount of time (for instance one hour). The same settings are also going to be optimal for getting to a particular image quality in the shortest time possible. If you run the calculations either in SharpCap or in a spreadsheet calculator, you will notice that the recommended gain, exposure and offset values don't change if you change the total imaging time.

Hope that makes sense, Robin

Re: Picking the correct exposure for Deep Sky

Posted: Mon Mar 16, 2020 2:48 pm
Hi Robin,

Thanks, I think I understand. I like to plan my astrophotography sessions and would be interested in spreadsheet to calculation the number of frames for each object before imaging. Where do I find the spreadsheet?

Mark

Re: Picking the correct exposure for Deep Sky

Posted: Mon Mar 16, 2020 6:40 pm
Hi Mark,

As far as I'm aware there isn't a spreadsheet readily available with these calculations in (unless somebody has followed the discussion above and put the calculations into their own spreadsheet). I was just commenting on the possibility of making that sort of spreadsheet if you felt inclined.

Cheers, Robin

Re: Picking the correct exposure for Deep Sky

Posted: Tue Mar 17, 2020 12:52 am
Mark,

You can check out my site here: https://snrcalc.now.sh/

The code is open source and available at GitHub (scroll down to the footer for a link). You can create a spreadsheet if you want from the formulae in calculation.service in the core/services folder.