A variation on using the CCD to see the donut of an out of focus star image
is to use a Hartman (Hartmann?) mask - I use a 3-hole mask - and try to
tighten the triangle of a slightly out of focus star image.

I'm trying this approach and it seems that an out of collimation image shows
an other than equilateral triangle. Line up the three holes with the
adjustment screws and it's easy to link the star spots with the screws by
covering the holes one at a time.

This seems promising, but I can't say yet if it's superior to other
approaches.

Jim Sgt.

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