It would be really nice to have a flat module that helps with taking sky flats.
When shooting sky flats at twilight for example, the light changes fast and you potentially need to adjust exposure time for each flat frame to get the same desired ADU.
And different filter also need different exposure times.
If Ekos could be told what the desired ADU is, it then could take an image (or a couple) to find out the best exposure time and then start a sequence that adjusts each frame to match the set ADU based on current time and some algorithm how much dimmer the sky gets each second.
Much like similar functions that exists in for example CCD Commander.
Hmmm, that's a good idea, I remember taking all the flats manually, it would be nice to have this somewhat automated.
I guess we can add a % desired ADU, then Ekos takes two images to find out the "Slope" and use that to estimate the exposure time given desired ADU... if the light changes, it adjusts the time accordingly. Ok, sounds good in theory, let's see if it can be implemented.
I gave this feature a try with my Canon 1000d and the Aurora Flatfield foil. I believe ADU is een CCD value, but wanted to try it anyway. I got the following result:
2015-12-13T15:41:02 Current ADU is 6.2% Next exposure is 64 seconds.
2015-12-13T15:40:34 Capturing image...
2015-12-13T15:40:34 Current ADU is 3.7% Next exposure is 2.7 seconds.
2015-12-13T15:40:06 Capturing image...
2015-12-13T15:40:06 Current ADU is 2.5% Next exposure is 0.15 seconds.
2015-12-13T15:39:39 Capturing image...
I started with a 0,1 second exposure. 64 seconds will result in a somewhat overexposed flat
Will it be at all possible to use this feature with a CMOS chip DSLR? What does it measure now if it isn't actual ADU?
It's been some years since i've fussed with a dslr, but from what I remember, there is an easier way to get proper flats using one. Instead of trying to manually adjust exposure times, put the camera into automatic, and let the camera figure it out on the fly itself.
As for twilight sky flats with a dslr, I'm not sure that'll work very well. I played with automatic flats some years back, and came to the conclusion that there isn't enough time during twilight to get flats from all 7 filters, as the light level is changing rapidly, and the narrow band filters take significant exposure times to reach the required levels. But I did find I could 'almost' get a full set if I started when it was still fairly bright out, and did all the narrow band filters first, then the colors, and do luminance last. But I was never happy with the results when trying to automate sky flats. When we were setting up to do a precision photometry run, I could get a really good set of sky flats, if I only did one or two filters, ie the ones we would be using for that nights run.