This is to document that I too have had dewing problems, from my very first imaging session a couple of days ago.
During imaging (set point -20C), it became clear that ice crystals were gradually growing from one of the long sides (bottom) of the sensor. By the end of the evening, this was taking up almost half of the sensor area.
At the end of the evening, the problem was captured through the use of Flats – which were unusable during subsequent image processing.
I attach a sample Flat, so the extent of the problem is clear.
During processing, it was obvious that there was also a more general dew problem in terms of a general 'clumpiness' throughout much of the frame. This manifested as a granular texture. This was mitigated through moving the black point – which was OK for stars, but tended to interfere with nebulae. The granularity disrupted the representation of fine detail with the nebula.
These problems will almost certainly affect my previously-prepared dark libraries – which will need to be replaced once the problem has been resolved.
I will work through the options documented in this thread, but can see that it may be necessary to open up the camera periodically to dry out the dessiccant tablets.
A better-sealed camera would be the way forward.
