Re: [ATM] Favorite Spider Designs

["vladimir sacek" <vla@toast.net>]

John,

>>If this spider mask is as effective as it seems to be,
>
> Suiter and Zmek weren't too impressed with it. Their simulation shows 
> diffraction spikes...

You've got me intrigued by the discrepancy in what the two side appear to be 
saying. But, then I realized that I'm - again - guilty of not using this 
little of brains that I've got.
What has impressed me most - and seemed to be the ultimate proof of the 
efficacy - about the apodizer effect were the PSF shown. As always, it's all 
in the way you look at it. And I looked at those PSF as presenting a 
circular aperture PSF combined with the spider vane effects. However, those 
are the PSFs of the spiders alone, in the direction of the intensity 
extension.

This means that the first minima width of these PSF is actually wider than 
the Airy disc radius by a factor of (Pi)D/3.83t, D being the aperture 
diameter and "t" the vane thickness (the vane being, in effect, a "negative" 
narrow slit). In other words, the main, central section of the spike (or 
spikes) didn't change significantly; only the following fainting maximas are 
nearly eliminated. The problem is that it is, at least for the amateurs, 
pretty much insignificant. It is the central spike PSF maxima that is most 
pronounced visually; it is where is contained - if I remember correctly - 
about 90% of the total spike energy.

Thanks for helping me to straighten that out.

Vlad


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