From: "Richard F.L.R. Snashall" 
To: atmlist 
Reply-To: "Richard F.L.R. Snashall" 




Bob May wrote:
> The Strehl ratio is determined in the monochromatic world.  Thus, a singlet,
> even at a very short focal ratio, can produce a very good number despite
> poor color correction.  You need to calculate the Strehl ratio for the
> unfocused part of the image also and that will indeed kick the number down.
> Bob May


The Strehl ratio I was quoting was the Polychromatic Strehl Ratio given in
OSLO (ZEMAX gives somewhat higher values).  As an experiment, I changed the
weight of the 650 nm wavelength to 1.0 (up from about 0.1) and recalculated
this Strehl Ratio; it dropped to .758 in the field center.  I assume from
this that the Strehl Ratio calculated by OSLO weights all the wavelengths,
even though it only lists wavelengths 1, 2 and 3 in the window.  In this
case, I used eleven wavelengths from 450 nm to 670 nm.  I believe that this
would give a good measure of Photopic Strehl Ratio, provided that OSLO does
not recalculate a new image centroid for each wavelength.

        Rick S.

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