Re: auto-collimation & postscript

[erker@xxxxxxxxxxxxxx (Greg Erker)]

>Sam Brown's "All about Telescopes" (from Edmund Scientific) has a
>section on building an optical bench and collimator.  You can measure
>the focal length of a lens either by measuring the images size of a
>test target (basically the projection method that Greg mentioned), or
>by auto-collimation.  Unfortunately auto-collimation requires a good
>(i.e., flat) first surface mirror.  The bench and collimator are
>pretty easy to make (the collimator needs a good achromat, 3 inch
>diameter with a 24 inch focal length is mentioned as being good for
>testing 6 inch diameter telescopes), and if you make a postscript or
>PCL file of the test target available on the web you wouldn't need to
>ship anything.

  I need to do my measuring with stuff I
have in the house in the middle of the
night. No auto-collam's.

  Re:postscript files. I'm a bit worried
about the geometric errors and slippage of
laser printers. In my experience the long
axis of the paper/transparency isn't quick
the size you expect but it is closer across
the width.

  If Bob and I print useing printers with
opposite distortions the cumulative results
may mess up our measurements.

Greg