Re: ATM "collimating" diagonals

[Dwight Elvey <elvey@hal.com>]

Jay LeBlanc <jaleblan@dakotacom.net> wrote:
> 
> At 03:22 PM 12/7/99 -0500, you wrote:
> 
> >How important or degrading to the image are these apparent misalignments??
> It becomes a question of how much astigmatism you can tolerate!
> Try using an artificial star like an xmas shiny ball in the sun in a well
> collimated refractor.  Put the diagonal in and shim the mirror while
> examining an extrafocal image.  Stop when it is nice and round!   -Jay-

Hi
 There is the other issue. If the 100% illuminated beam
hits near the center of the eyepiece, you can still point the
primary such that it will have a good diffraction image
at the center of the eyepiece field. This is still good
imaging, even though the secondary is not making the
100% field concentric with the center of the eyepiece field.
 So, there are two factors that the laser requires that
do not significantly effect the quality of the final
image. There is a Nils mention, slight tilt of the focuser
and slight off centering of the 100% field ( vignetted by
the secondary). Both of these will show as errors in the
laser tester while they are not really a big problem.
Worse yet, one may tilt the primary to compensate for
these putting the system into worse alignment. In order
to get good alignment with the laser, these have to be
finely adjusted before touching the primary. When using
the cats eye tester, these only need coarse adjustment.
Just my opinion
Dwight