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Doesn't this also assume perfect tracking with no drift at all between subs. Is that the case with your system? Dithering implies every sub is exactly the same without a dither command. I rarely see that even with high end mounts.
If you work your PA to perfection maybe but if you are using a higher PE mount I think it highly unlikely to the extent of 1 or 2 pixels or even more.
Another point not quite related is its common practice to bin your guider 2x2 as Peter pointed out. But if you can I think there is a gain by using 1x1 binning. Perhaps not practical if its hard to find a guide star.
SBIG STi has 7.4 micron pixels. Not sure about a Lodestar. 2x2 binned would 7.4 micron pixels would be the equivalent of 15 micron pixels. So if you are using a 9 micron pixelled camera you are already over 1.6 pixels. I suppose the guide star would land within that 15 pixel band at optimum but highly unlikely it would in practice and no doubt lands somewhere within several pixels. Even with good seeing sitting watching the guide star it changes shape all the time so the centroid would have to be moving around as well.
My point is even if you aren't deliberately dithering there would still be a significant amount of dithering occurring anyway as mounts PE, polar alignment drift, flexes and seeing are causing it to move around already.
Otherwise you wouldn't need a Protrack TPoint model if it were dead still sub after sub and within a sub.
But as an approach this is good work and it makes sense to make subs not replicate each other exactly.
Greg.
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