Re: [ATM] 8" Diagonal- More info

["vladimir" <svla@isp.com>]

With ~30% c.o. the second minima is nearly twice the (original) Airy disc,
or 10 microns in diameter. But an aperture of this size doesn't stand much
of a chance to have recorded this kind of detail. Even in 0.5 arcsec seeing,
it would still have D/r0 of ~2.7, and average long-exposure (several seconds 
and up)
stellar blur larger than 10 microns in diameter. In more usual seeing, it is 
likely
to be 20-30 microns. According to the theory, an average long-exposure RMS
seeing error for this aperture in 1 arcsec seeing would be nearly 0.7 wave,
a rough equivalent of 2 waves of spherical aberration. Surface smoothness
could be more of a factor than figure errors.

Vlad

> With smooth 1/4 wave (wave front) zonal errors, most of the light that
> is split out of the Airy disc goes into the first "gap" and the first
> ring.  Those are still inside the pixel size.  Higher frequency errors
> would throw the light a little farther out.
>
> Mark Holm

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