Re: [ATM] Ronchi Confusion

[Leftfieldstar@aol.com]

 The figure of a parabola is such that it reflects light from an infinite 
source, such as a star, to a single diffacrtion limited point of focus. This will 
produce straight lines when using a Ronchi grating at focus.
 A spherical mirror has only one point of perfect focus which is its radius 
of curvature, often stated as being twice the focal length of the mirror. A 
Ronchi grating will produce straight lines if the figure is of constant radius 
and the light source and observation point are at the radius of curvature; a 
standard Foucault test demonstates this. Any hooking that is observed indicates a 
difference of radii. 

Dominic DiLeo
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