Cooled Mono Camera: No correlation between the master dark and target frames

[Farzad_k]

Hello,

I know this question has been discussed a few times. I am still not sure what the answer is. I have read in another discussion that "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." The discussion was on a DSLR, but for a cooled sensor, should the thermal noise still be a reason for lack of correlation? Also, this warning only appears after image number five has been processed, meaning that the first five seem to be okay for some reason and the rest (nearly 40) are not.

Thanks for any insight.

[pfile]

what kind of sensor is it? some sony sensors have really low dark current and for that reason some people only use bias frames to calibrate.

rob

[Farzad_k]

I am not sure of the make of sensor, but the camera is a new ZWO ASI 1600 Cooled Mono. What is interesting to me is that the sensor temperature is controlled and the light frames and dark frames are all captured under the same conditions, except for the cover, of course.

[pfile]

what ImageCalibration does is that it iteratively scales the dark frame and subtracts it from the light, until the noise in the light frame is minimized. so if the dark signal is really small, it can't find a correlation between the scaling factor and the noise, and so it gives up and prints that warning. i believe in this case it sets the scaling factor to 1.0 and then subtracts the dark.

what duration are your subexposures and the dark?

rob