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

["B. Pepin" <atmjedit@conceptsnet.com>]

Hmm..tube currents.. don't you hate local seeing? Maybe real-time sampling
might have the effect of semi-adaptive optics to tighten up such a CCD
mirror test: Use an oversized tube (or tubeless mount) to eliminate gross
"pooling" effects in the instrument, use a pickoff mirror to divert the
image from one of the apertures, with relay lenses to equalize the light
paths and increase the effective f-ratio at both sensor locations (or chip
regions). Chop both light paths with a synchronized variable mechanical
rotary shutter, using the blackout to isolate sample images and determine
the location, speed, and intensity of any local currents, subtracting these
averaged sum local effects from the respective regions of the pixel data to
make a custom digital video filter, subtract the time-sychronized filter
over the mirror-test image data to neutralize the seeing effects.


----- Original Message -----
From: Bratislav Curcic <Bratislav.Curcic@ericsson.com.au>
To: atm <atm@shore.net>
Sent: Thursday, September 07, 2000 5:11 PM
Subject: Re: ATM Using a CCD imager to create a topographical map of
telescope mirror


>
> Anthony wrote :
>
> > It appears that, on your own, you
> > have invented the common path lateral shearing interferometer
>
> ???? 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 :
>
> > The problem now becomes one of separating the two star images so we can
=
> > differentiate between the energy distribution of the reference image and
=
> > the test image. I have thought of a number of methods for performing =
> > this separation.
>
> No inteference, no interferometer.
>
> As far as the idea, I'm afraid that good ol' atmosphere will make
> this test completely unworkable. The assumption is that atmosphere
> will deflect BOTH reference image and test image; the reality
> will be anything but that. Unless taking long exposures or doing some
> serious averaging, this test will simply measure tube currents.
>
> Bratislav
>