Re: Star Test Question

Jan R. Sugalski (afn19866@freenet.ufl.edu)
Tue, 2 May 1995 01:01:22 -0400 (EDT)

It is possible to test for astigmatism with a Ronchi grating. I do it all the time with refractor objectives. If you rotate the optics the lines will slant from the vertical. A lens with no astigmatism will show lines running at the same angle no matter how the lens is rotated. This is described in optics books. Jan

Pushing glass will set you free!

On Tue, 2 May 1995, Mark Suchting wrote:

> Date: Tue, 2 May 1995 10:57:42 +1200 (EST)
> From: Mark Suchting <masuch@dap.CSIRO.AU>
> To: atm@best.com
> Cc: Bratislav Curcic <epabcc@epa.ericsson.se>, atm@best.com
> Subject: Re: Star Test Question
>
>
>
> On Mon, 1 May 1995, Jan R. Sugalski wrote:
>
> > The ronchi test, especially with a
> > double pass of the light under autocollimation is extremely sensitive to
> > zonal defects and in most cases there is no real advantage to the star test.
>
> Astigmatisms that make otherwise great optics useless ( ie 1/2 a wave or
> more ) are literally impossible to detect with a ronchi screen, where the
> star test shows it up easily. These tests should always be used together,
> I think, to give you the whole picture.
>
> Mark
>