Re: [ATM] Anastigmat

[Richard <cnc@cncservo.co.uk>]

Hi Richard,

Thursday, December 6, 2007, 1:15:48 PM, you wrote:

RFLRS> Not really.  Astigmatism is corrected in the field, with an
RFLRS> S-T crossover usually somewhere just inside the edge.  The
RFLRS> field diameter will not scale with the 'scope.  The maximum
RFLRS> field, in degrees, will vary inversely with the 'scope size.
RFLRS> The net residual astigmatism will also decrease as the 'scope
RFLRS> gets larger, since it typically varies as the cube (?) of
RFLRS> the field.

If we increase the diameter by scaling the whole scope, but keep the
same f/ ratio, we wouldn't change the field angle. It is exactly
analogous to looking at the design from closer or further away. If you
choose to fix the field *diameter* then you are, in effect, choosing
to vary the field angle with diameter, but that is not scaling (a word
I chose carefully :)

-- 

Best regards,
  Richard in the UK

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