SEC: UNCLASSIFIED RE: ATM Collimation Question

[afmartyn@raaf.defence.gov.au]

One thing you should be aware of is that the star 
image and its secondary shadow will be different if 
you offset your diagonal. If you don't offset your 
diagonal then when you do an optical alignment during 
then the you will find that very little change will be
 required when you align doing the star test. In fact 
I generally find if I do a good optical alignment then
 I usually don't have to do an alignment when checking 
the star test (and I don't own a laser). However, if
 the secondary is offset, ie away from the focuser and
 down towards the primary, then even if you do a 
perfect optical alignment, the secondary shadow will 
still be off centre in the star test. If you then 
centre the secondary shadow by adjusting the primary 
alignment then you are in fact making the alignment 
worse. So as far as I'm concerned, the star test 
alignment only works for non-offset diagonals.