Remember that low value can actually be a benefit because it means you can take advantage of subexposure integration and get better pixel rejection and a reduced penalty for an image with defects.
This is turning out to be more complicated than I expected when I first decided to 'write a simple script to learn the API'
No matter how many sub-frames you want to stack, there is going to be a limit in total exposure time, call it T_{Total}. The final combined stacked photo’s total noise term, will be
(http://www.cloudynights.com/images/optimal_files/image108.gif)
Where: E_{Total} is the total noise for a shot of time T.
S is the sub-frame length in units of time T
T_{Total} is the total time in units of time T
Thanks Sean. Works fine now :)
I am not understanding something though: I image from 6800ft, at a location where we have a 21.5SQM skies.
And the ExposureCalculator is telling me that the suggested exposure should be 53 seconds?
How is that possible?
I'm also getting some 'unusual' figures for my Luminance subs - suggested exposures of 16s on a 300s Lum sub???
With his help I have updated the script to use equation (16)
is there a practical purpose for the 4 hrs (14400 sec) total exposure time
Can those of you with crash problems please try the most recent version on GitHub https://github.com/seanhoughton/CalculateSkyLimitedExposure (https://github.com/seanhoughton/CalculateSkyLimitedExposure)? If it fixes the crash I'll post another release here. This might be something that Juan has to look at with a debug build of PixInsight.
I've been considering adding some charting to the script to provide a more intuitive look at what's going on as the sub-exposure length changes
Use the formula to determine the practical upper limit of the total time for a given sub-exposure and know that if you are thinking of possibly putting in even more total time, you need to use a longer sub-exposure to be safe.
So..... Do I just use a preview from a single un-debayered sub and unstretched sub? If I do that I get a max exposure of around 2.5mins which is not good :-[ Also how/what is the pedestal value?Deduct a 600s Dark frame from the Light and try. ;)
I have been taking 600s images in the hope that I can bring out some faint detail but it now seems that 2mins is it and any more is pointless :-\
Ah.... I don't bother with darks as the qhy8 does not need them, or so I was told ???Anyway you must subtract Dark for correct calculation. But, if your camera have zero dark current, you can subtract bias frame.