Re: [ATM] how accurate is the foucault test

[John Lynch <john_p_lynch2004@yahoo.com>]

David,

Yes, you can take the average knife-edge position
between center zone (closest to mirror) and outer zone
(furthest from mirror), and add this to the
measurement that you make from mirror edge to
knife-edge position for the center zone using a tape
measure.  AND, don't to forget to add the sagitta,
which can be calculated.  This will give you a very
accurate estimate of the focal length of the mirror-as
good as you need to know to drill holes in your
telescope tube.

Texereau and Howard books have good explanations about
the Couder mask.  I would highly recommend using
individual masks for each zone, and make sure that the
"window pairs" for each mask are centered about a
horizontal line across the middle of the Couder mask. 
This technique works great, and once you start your
testing you'll get the hang of it.

Regards,

John Lynch



	
		
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