darks and binning

[antonio]

Hello,
I have just met PI and I am impressed by the overall project!
I would like to start processing directly from PI, but from tutorials it is not clear to me whether I need a single bias/dark sequence at binning 1x1 or if I need a separate one for binning 2x2.
From what I learned, PI is able to figure out recalibration with different exposures lenght or temperature, but probably it would be better to start from 2x2 binning, instead of obtaining from 1x1 files, wouldn't it?
Thanks,

Antonio

[sreilly]

I have always used the same bin calibration images for the lights. While you can scale a dark I don't think this works for using 1x1 calibration frames on a bin 2x2 image or vice versa. Using nights that aren't suitable for imaging makes it easy to build a library of darks at different bin rates you use and if I remember correctly 6-10 is about all you need to use for a master frame.

-Steve

[antonio]

Thanks, Steve!
So you basically confirm my feeling: doing mostly LRGB/Ha at 1x1 (L,Ha) and 2x2 for RGB, just one series of bias/darks at a single exposure for each binning choice should work. That will be a considerable saving, since currently I take darks for all the exposure range I can use (1,3,5,10,20 min) because I am not sure Nebulosity can handle rescaling as well as PI. As for the number of darks, you suggest the same number as I currently take for preprocessing in Nebulosity, but in PI tutorials they recommend more: in any case, planning a single exposure series with 20 frames is perfectly acceptable.
I assume flats at 1x1 binning should suffice, instead, since resampled flats at 2x2 are readily prepared.
Sorry for such basic level questions, but as you know these are most important issues for correct starting preprocessing flow.
Regards,

Antonio

[sreilly]

There is a tutorial on Master Calibration Frames that explains this very well. Below is an excerpt from that:

"Acquisition Notes

As we'll see in this article, the dark scaling algorithm implemented in the IC tool works better when read noise is negligible in the master frames. IC is optimized to work with calibration libraries: don't worry about differing temperatures and exposure times between dark and light frames. IC will always rescale the dark noise to match every light frame.

It is also very important to have a bias library, because thermal noise must be bias-subtracted: only thermal noise must be rescaled in the master dark to match the thermal noise in the light frame.

After experimentation, I highly recommend taking at least 10 dark and bias frames. Never use less bias than dark frames, because this would introduce too much read noise in the bias-subtracted master dark: a 50-frame master dark will have almost all the read noise of a 10-frame master bias.

Don't waste time acquiring dark-flat frames: IC will rescale the master dark to match the dark noise in your flat frames. "

The full tutorial is here.  http://www.pixinsight.com/tutorials/master-frames/en.html  Much better than I can explain. Just remember that the master calibration frames you create in PI won't work in other programs such as MaxIm or CCDSoft. Having used the tutorial and gotten use to image calibration in PI I get the impression that I get a cleaner result. I haven't tried to prove that but it's my impression.

[antonio]

Thanks Steve, I read the tutorial indeed but it left me with some doubts about binning. Now I am more confident I understood and will definitely give it a try!
Regards,

Antonio