The shutter is a bit of a dissapointment! It fails 30-50% of the time, and there is considerable variability, and bias, in the exposure durations. Only for 1s exposures is the scatter less than 0.1% and the bias negligible. We have heaters on the shutter, but apparently not enough. Low temperatures ('below 5C') are supposedly not acceptable - yet we see failure at 9-10 C.
We also see 'dragging' of the image. [Image needed here!] This used to be due to the shutter staying open after the image started reading out. We see a variation on this: For the overexposed images of various stars blooming occurred in th evertical direction - well, 'dragging' of these spurs occurred in the image. This is hardly anything to do with photons arriving on the image during readout but is some issue related to electrons and their transfer from column to column - perhaps suggesting that the previous 'dragging' also is related to saturated or highly charge pixels.