Re: Turbulence and diaphragm

Mitch Alsup wrote:
A Gaussian Aperture is a mask that sits on the front of a telescope
that reduces the amount of light entering the outer edges of the
telescope. Idealy the limits resemble a Gaussian curve (Bell curve). In
practice, one only needs to reduce the light at the very edge of the
aperture by 60% (40% of the light remains) to get a good effect. This
gets rid of the Point-Spread function effects on the airy disk and
gives a nice clean spot without diffraction rings.

It does *not* get rid of the PSF. (I know you didn't mean that, but the
original poster might not.) What it does is eliminate the dark gaps in
the PSF that lead to rings. It also makes the PSF somewhat more compact
and generally dimmer (as you've noted). Compact, good; dimmer, bad.
But possibly not so bad, depending on the application.

A true Gaussian mask leads to a Gaussian PSF, I think. But any physical
mask is stopped by the aperture, which leads to some non-Gaussianness in
the PSF. This discrepancy is generally small enough to ignore,
especially in larger telescopes (where turbulence effects dominate).

--
Brian Tung <brian@xxxxxxx>
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