Re: strehl ratio for obstructed scopes

From: Richard F.L.R. Snashall (rflrs_at_notrcn.com)
Date: 10/11/04 

Date: Mon, 11 Oct 2004 23:26:05 +0100

Vladimir Sacek wrote:

>jonisaacs@aol.com (Jon Isaacs) wrote in message news:<20041011071440.29660.00005715@mb-m16.aol.com>...
>
>
>>I was under the impression that the Strehl Ratio had a specific definition and
>>that that definition does not take into account the CO because the SR is meant
>>to be a measure of the quality of the optics in a given scope, not the measure
>>of the optics and the design.
>>
>>
>
>Jon, that is correct, and the definition describes the Strehl as a
>ratio of peak intensities of an aberrated vs. perfect system. Since
>aberrations are deformations of the wavefront, the Strehl indicates
>quality of the wavefront. CO doesn't deform the wavefront, although,
>similar to wavefront deformations, it does affect wave interference at
>the focus by blocking portion of the wavefront. The Strehl is by
>definition tied to the effect of aberrations; since CO doesn't deform
>the wavefront, it is not one of them, and is not covered by the Strehl
>(and so is not the effect of chromatism).
>
>
By the same token, it does not include vignetting. If a system with a
0.99 Strehl ratio is vignetted
down to 70% transmission, the Strehl ratio doesn't change. Seems kind
of "wrong" to me for
some reason.

>Vlad
>
> 

-- 
Rick S.
http://users.rcn.com/rflrs

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