Optimum Subexposure Calculator (and more...) - Forums

Topic starter

Jul 2, 2021

Hi,

I wanted to let here my spreadsheet about calculating Optimum Subexposures for a given combination of equipment and sky conditions. It is based on the widely accepted criteria about the impact of the Readout Noise in the SNR. I have to say that I'm not an expert in this field and this document has to be taken as a simple summary of the formulas I have been learning from the people that really knows a lot about this stuff.

The spreadsheet works by filling some parameters (the ones in yellow) and it calculates the results. One key step is that we need to take a test exposure with the specified equipment, to calculate the Background Flux and use it as a reference to give the Optimum Exposure Time for this conditions. Apart of the Optimum Exposure, I added some other calculations that can be useful to plan the astrophotography sessions needed for a given project, for those (as me) that invest in long integration projects.

I had this spreadsheet in my website time ago, but I never invested time in to give any instruction. Today I had an agenda gap, so I could write some explanations into a post:

https://aiastro.wordpress.com/2021/07/02/optimum-subexposure-calculato
(As told, don't expect any mathematical demonstration, although there are some links with more in deep theory.)

Hope it helps!

Helpful Engaging Supportive

Kelvin Hennessy

Jul 2, 2021 · Edited: Jul 2, 2021

Thank you Alberto - this could be a real time saver. I've studied and used the sub exposure tables developed on cloudynights for my ZWO cameras and also created my own spreadsheet based on the calculations but this looks so much more thorough and easier to use.

Well Written Respectful

Claudio Tenreiro

Jul 2, 2021

It certainly should help, once you get all the input data correctly into the spreadsheet. This goes inline with a talk by Robin Glover, mentioning a few aspects that helps to select proper cooling of the camera and exposure time. I am not qualified to contribute since I am still in the first one third of the learning curve…
As you mention, background is a bit important, and maybe, in my case, it is an issue. So thanks for bringing that up here and providing your web pointer. I will certainly try this.
CS !

Rick Veregin

Jul 8, 2021

Wow, this looks really great, being able to virtually put in different options then being able to explore how it affects exposures! A great planning tool that can be used when we can't image–sadly less and less with global warming, more clouds, smoky fires and brilliant satellites…

I do really also like SharpCap's Smart Histogram for on the fly adjustments to imaging setup during the night. The neat thing is when you go to image you can use it for the current conditions and camera to automatically calculate how exposure time and bit depth are going to affect your image. All you need to do is a quick capture of a background area of the frame, and it then calculates everything from your current camera settings. Make a quick adjustment to your settings and you are good to go. Sky brightness varies with the altitude of your DSO, haze, and of course varying light pollution, as well as time of night. So SharpCap can enable you to make a quick on the fly adjustment to your settings as you need them for changing conditions.

Fair warning, SharpCap Pro costs <$20 USD/yr, but also has an awesome FOV plate solver polar alignment around Polaris, which is worth the price alone in my opinion.

Clear skies everyone
Rick

Helpful Insightful Respectful Engaging Supportive

Related discussions

Fullwell Capacity – Does it really matter?

Hi! With CMOS cameras you are being told to use a readout mode with a high fullwell capacity (FWC) for deep sky objects, so your stars won’t burn out that quickly. This is one of those things you usually don’t question, because it sounds plausible. H...

Fullwell capacity affects SNR calculations relevant to subexposure optimization.

Apr 15, 2023

Hello from Los Angeles

Hi Everyone! I'm new to astrophotography (only been doing it for a few months) but I'm fairly experienced with visual astronomy and did some work in radio astronomy for a couple years. I got into astrophotography when I got asked to teach a c...

Technical tool for optimizing equipment settings in astrophotography.

Apr 16, 2020