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Hi Norm,

> I have a question. If the two stars are smeared because of camera motion,
> why is the ISS track so narrow? What am I missing?

The ISS track is the vector sum of its own motion and the camera
motion.  For these short exposures, the camera motion is a simple
unidirectional translation, though there is an ambiguity as to which
end of the star trail is "first".

Theoretically the camera motion could be anything that resulted in the
linear star trails shown.  A rapid back-and-forth would indeed have
resulted in a wavy ISS image.  But the image stabilizer strongly
attenuates that kind of camera motion.

The width of the ISS image will be some combination of focus error,
sensor resolution, interpolation filtering from the Bayer matrix, and
intrinsic source size.  Also in this image it is saturated, the
unfortunate result of lack of raw mode.

Cheers,
Peter

   

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