To: atm{at}shore.net
From: Jim Burrows 
Reply-To: Jim Burrows 


At 07:51 2003-06-05 -0700, Jeff Anderson-Lee wrote:

>The amount of refocusing is generally small.  For the example 8x1in f/6
>pyrex mirror with a 3 point cell, it is -0.0255 (millimeters?).  I don't
>know how significant this would be when doing extended tracking, I just know
>that using refocus off avoids this difference.  Your milage may vary.

I had to dig out Born & Wolf for focus tolerance, p. 491:

         ñ2(f/)ýL, L=wavelength

For f/6 and 550 nm, .0396 mm - so you're pretty close.

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

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