Re: Single or multi hole off-axis filters?

From: Chris L Peterson (clp_at_alumni.caltech.edu)
Date: 06/10/04 

Date: Thu, 10 Jun 2004 00:22:47 GMT

On 10 Jun 2004 00:15:26 GMT, jonisaacs@aol.com (Jon Isaacs) wrote:

>So how accurately do the holes have to be cut to provide that alignment?

Not at all. You can hack a Hartman mask out of a paper plate with a pen knife.
If you make a mask with a collection of randomly located holes, you will see
that same pattern reflected in the multiple star images when out of focus. When
in focus, you will see a single star image. But note that at high magnification,
you will see a distinctly non-circular diffraction pattern around this single
star image. There may be special cases where such a mask provides good results
(such as looking at double stars of the appropriate spacing and angle), but in
general, such an aperture will not yield better results than a simple,
unobstructed circle.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com