Weird Artifacts in Calibrated 1x2 Mosaic.

@rixon Many of the black squiggles have similar shapes which indicates that they are cold pixels that squiggle through the image due to drift during imaging. It could be that the raw lights show very short squiggles or single cold pixels, depending on how much drift happens during a single image. This seems to indicate that your flats don't fully correct the cold pixels or, if the cold pixels already show up as squiggles in the raw images, completely fail to correct for the cold pixels because they aren't pixels anymore but short squiggles. In the flats they would be single pixels so they'd be very hard to spot.

Hi Wouter, What settings should be turned on in the calibration step to prevent this? 

@rixon First you'll need to inspect the raw lights to see if there are dark squiggles or only cold pixels. You can do that by inverting the image such that white becomes black and vice versa, for instance by exporting to TIFF and then opening in an external image editor. if there are little dark squiggles then you cannot correct those with flats.

However, if there are cold pixels (which should show up as bright single pixels in the inverted image), you can set the value of the integrate drop down of MasterFlat to a different value than "automatic". Then choose an outlier rejection filter and set the kappa low and kappa high values. When you hover over the drop downs, you get an explanation of what each setting does. You'll need to select the outlier rejection filter that applies to your amount of lights (which is what "frames" refers to) and then play with the kappa values until you get a good result.