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[ATM] How many zones

At 2004-02-17 08:51 -0800, Jonathan Bishop wrote:

>I am figuring an 8" f5 mirror. Can someone recommend the number of zones 
>to measure? I read Tex and he discusses using 4 zones, but that is for an 
>8" f8 mirror (or was it f6).

Nils Olof Carlin has a program to find the required number of zones:

         http://www.atmsite.org/contrib/carlin/couder

Alternatively, you can put your readings into Sixtests plus an estimate of 
how accurate the readings are (take several readings to find the 
scatter).  The program will output the surface RMS and a 1-sigma confidence 
interval around that RMS value.  The size of the confidence interval 
depends on the number of zones and, of course, the reading accuracy 
estimate.  A quality optic has a surface RMS of about 20 nm, so if the 
program says RMS = 15 ? 5 nm, there's a 16% probability that the mirror 
doesn't pass.

         -- Jim Burrows
         -- mailto://burrjaw@earthlink.net
         -- http://home.earthlink.net/~burrjaw
         -- Seattle N47.4723 W122.3662 (WGS84)