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Old 21-12-2017, 03:17 PM
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ChrisV (Chris)
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Calibrating with darks in pixinsight - ASI071 camera

I just got my ASI071 upgraded to the pro. When I calibrate the flats with the bias/darks in pixinsight I get this error.

** Warning: No correlation between the master dark and target frames (channel 0).

I thought I'd done something wrong with the camera temperature so redid all the calibration files - 100x bias frames (0.05sec), 40x dark frames (90sec), and 40x flat frames (0.15sec - optimal exposure set by APT). I've made these at -5C as this is where 071Pro reaches near minimal dark current of 0.008 e-/pix/sec (https://astronomy-imaging-camera.com.../asi071mc-pro/).

The error only happens when I use the darks, it doesn't happen if I use just the bias frames. I went back and used the calibration files from the camera before I upgraded it and get no such error.

I've looked up the PI forum and maybe the problem is that with the short flat exposures I don't need dark frames to calibrate the flat frames ?

Inspecting my calibration files in PI, the master calibration files: the mean(average deviation) are
- Master Bias = 268.5 (3.5)
- Master Dark = 270.1 (4.0) in ADUs (16 bit)
So does this suggest that darks aren't even necessary for these exposures on my camera?
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Old 21-12-2017, 04:05 PM
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Atmos (Colin)
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I’d suggest that either one is debayered (RGB) and the other isn’t OR they’re slightly different geometries; different number of pixels.
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Old 21-12-2017, 05:29 PM
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Quote:
Originally Posted by ChrisV View Post
** Warning: No correlation between the master dark and target frames (channel 0).
This is common with flats where the exposure time is a lot shorter than the darks. Here's what Juan Conejero wrote on one of the many threads about this...

Quote:
Those warning messages are telling you that the master dark frame you are using has no correlation to the light frame in terms of thermal noise. In other words, if the master dark frame is subtracted from that light frame, then the result will always have more noise than the original. Hence, a zero dark scaling factor is being applied, which is equivalent to not subtracting the master dark frame at all.

The noise evaluation routine implemented in our ImageCalibration tool is very robust, so in general my advice is trusting it. We still haven't seen a practical case were it fails to compute an optimal dark scaling factor.
It's a warning you can safely ignore.

Cheers,
Rick.
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Old 21-12-2017, 07:18 PM
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Quote:
Originally Posted by Atmos View Post
I’d suggest that either one is debayered (RGB) and the other isn’t OR they’re slightly different geometries; different number of pixels.
I checked. None are debayered. They have the same pixels/geometry.
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Old 21-12-2017, 07:21 PM
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Thanks Rick. So maybe I'm best using just bias frames and no darks - there's not much diff between my darks and bias frames. And dither to take care of the few hot pixels
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Old 21-12-2017, 07:30 PM
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Originally Posted by ChrisV View Post
Thanks Rick. So maybe I'm best using just bias frames and no darks. And dither
That's what I normally do, Chris.
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