Re: [ATM] 7 inch sphereical mirror

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

Richard wrote:

>If your figures are correct, and a Strehl of 0.92 corresponds with an
>RMS spot size of twice the Airy disk size, then it makes a very good
>case to never use Visual Strehl as a guide to optical performance.

Richard's figures seem correct; it is only that the last one gives actual 
blur diameter at best focus, not the RMS blur. The RMS here is ~0.85 times 
the 550nm Airy disc.

For lower spherical aberration, the RMS blur at best focus is smaller than 
the geometric blur by a factor of ~0.408 (slightly rounded off). In units of 
Airy disc diameter, the RMS blur diameter is ~121D/F^3 for D in inches and 
550nm wavelength.

Slight variation in the RMS radius probably comes from not quite radially 
symmetrical ray distribution with spherical aberration.

Vlad 

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