I revised the Gain and Sub-exposure calculation spreadsheet for the ZWO ASI183 and developed a new one for the ASI294.
They are too large to attach, so I setup a read-only Google share drive:
1. Much of the theory and equations came from Jon Rista, Frank, Craig Stark, and others (Thank you!)
2. Blue boxes are for user entry, everything else is calculated for you. If you don't want to use image data to calculate the sky background and camera dark current, just enter those values directly to the best of your ability.
3. The "Transmission Efficiency" of the entire optical system is likely the largest potential source of error. Play with it until your data matches a hand-held SQM, or known sky brightness value. This may change with different filters. I find 0.5 to 0.7 works for me.
4. The common thinking is you want a Swamp Factor of around 10. However, with narrow-band, especially at darker sites, this becomes impracticable.
5. The 183 tables go from Gain 0 to 270, but Jon Rista warns to not exceed Gain 178 with that camera.
6. I arbitrarily fixed the "object signal" to 22.0 magnitude/square arc-second. This is to compare imaging an object from two different sites, with different sky brightness, so as to have an apples-to-apples comparison. If you actually know your object's brightness, change the "22" in that equation to the desired value. This will only affect SNR calculations.
7. It is just a guide. No precision was intended.
8. The 183 spreadsheet is not all that different form the Gain and Sub-exposure tables posted here:
Special thanks to Nik Coli, who has been running these spreadsheets on his 183 and 294 and finding and fixing all my errors.
Edited by StevenBellavia, 12 August 2019 - 03:33 PM.