From: Patrick Hudelot 
To: scottythefiddler 
cc: ATM 
Reply-To: Patrick Hudelot 



Qualitatively I d say that the Strehl ratio is the ratio of the Amplitude
of an image of a point source through an instrument (including atmosphere
or not) by the amplitude of the perfect image of this point source.

I m pretty sure it s related to the surface distribution but I heard the
definition with the amplitudes ...

Patrick

On Wed, 9 Apr 2003, scottythefiddler wrote:

>
> For the past several days, I have been 'googling' trying to find out more
> about the Strehl ratio, especially how it is calculated, and what it
> 'really' indicates.  The following is the best that I have been able to
> find:
>
> ((RMS * 2 * pi) 2 -/+ ) Inv Nat Log
>
> on a web page at http://www.rfroyce.com/standards.htm
>
>  The inverse natural log of ...?  Aren't there 2 other values needed to
> calculate the inverse natural log, and if so, what are they.
> Does anyone have a complete expression for the Strehl ratio?
> Does anyone know of a web page with a comprehensive discussion of the strehl
> ratio?
>
> >From what I have found so far, it appears that one could postulate a surface
> which merits a Strehl ratio of 1, (presumably perfect), but which also
> 'spills' some light outside the airy disk into the surrounding rings.    The
> strehl ratio has often been described as the ratio of light which reaches
> the airy disc compared with a perfect aperture.  However, it does appear
> that the Strehl ratio is somewhat different.
>
> What am I missing?
>
> Scott Donaldson
>
>
>

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