Re: ATM Using a CCD imager to create a topographical map oftelescope mirror

[Anthony Stillman <atmer@flash.net>]

I agree, it is hard to see where interference "comes into play".  This is
never the less an example of a simple achromatic lateral shearing
interferometer.  The two pupils in the mask function as a diffraction
grating.  Each order of the "grating" is a lateral shear.  The interference
of these sheared images is what the sensor array detects.

As Bratislav and David note, shuttering the pupils or for that matter
introducing a pi/2 polarization shear spoils the interference. In so doing
it reduces the test's potential sensitivity an order of magnitude, possibly
more.  I ignored this intentionally and hoped to convey encouragement,
elicit research, investigation and study.

Anthony


David Hill wrote :
>>>...place a mask in front of the mirror and imager so that only
>>> two small circles of light were allowed through...

Anthony wrote :
>> It appears that, on your own, you
>> have invented the common path lateral shearing interferometer

Bratislav wrote :
>???? How did you come to that conclusion ? I though that David described
>simply a dressed up Hartmann test. I can't see the interference occuring
>anywhere, especially as David insists on separating the images by using
>shutters and/or filters

David Hill wrote:
>...I intended it as a test to calculate the shift in position...
>...I am not seeing where interferometry comes into play. In fact, the
>practical
>implementation of the test I described never allowed the light from both
>openings to hit the CCD at the same time.