Re: Star Test Question
Chuck Grant (grant@aretha.llnl.gov)
Fri, 28 Apr 95 12:35:35 -0700
> From: epabcc@epa.ericsson.se (Bratislav Curcic)
>
> This is the exact reason why star testing is NOT really a reliable
> source for optical testing. In other words, it's not QUANTITATIVE. It
> will tell you if you have perfect optics, but when it is NOT perfect,
> it is very difficult to tell what is wrong and more importantly BY HOW
> MUCH.
>
> Your case sounds to me as a typical UNDERCORRECTED mirror, i.e. outher
> zones focus closer than a central ones. But there is so many possible
> causes for symptoms you've described that is almost impossible to say
> without actually looking thru. Why don't you take a Ronchi grating and
> have a look ? That will immediately tell you the full story.
>
> Bratislav
>
Page 29 of Richard Suiter's book shows an example of an undercorrected
start test, more examples are on pages 182, 184, one 186, pages 183 and
185 show two undercorrected and one overcorrected set of images.
In all of these undercorreced pictures:
the outside ring is brighter inside of focus,
the center is brighter outside of focus,
the rings are more distinct inside of focus.
It does seem kind of counter-intuitive.
Chuck