Kring dithering doesn’t come in to play at all
Of course dither matters. You cannot be exposing while dithering is occurring. The idea of dithering is to move a point in the sky to different places in the sensor, so that after stacking, you average out the artifacts on the sensor.
Exposure has to be stopped before a dither is started, and new exposures are only resumed after the mount has resettled at the new location. This places a star at a different location on the subsequent frames, and the stacking program will compensate by aligning all sub frames to a reference frame.
With two cameras, you will need to wait for both cameras to stop, before dithering and then starting exposures again.
The term "dither" is hijacked from the signal processing world where a small noise is added to the incoming analog voltage before giving the voltage to an A/D converter. This reduces the artifacts from the discrete steps of the converter. Although the output ADU is noisier, on average, you have improved the granularity of the A/D converter. For example, when applying a voltage of 2.42, the dithering noise will cause the A/D converter to sometimes put out 2, and sometimes put out 3, instead of always putting out 2 when undithered. If the noise is uniformly distributed with an amplitude of 1, the fraction of the measurements the A/D converter puts out 2 vs the number of measurements it puts out 3 will end up after averaging lots of samples and converge at 2.42.
Chen
