Re: ATM Off Axis mask

[andydtg@phoenix.net]

Bruce Swayze writes:

My brother and I experimented
>several years ago with various configurations of aperture stops using two,
>three, or more holes cut out, and it just doesn't work.  You will find that
>the double, triple, etc. images just do not focus together properly, and you
>end up with a mess.  It defeats the idea of an aperture stop in the first
>place; that is, to give sharper images and less glare.  I don't know if it
>was due to extremely minute errors in collimation, or what, but the idea
>just doesn't hold water with me.

I suspect the 'misaligned' images are just due to the reason one uses 
masks in the first place - bad seeing. The full aperture image can be
considered to be made up of all the images formed by small areas of the 
aperture, in bad seeing they don't all line up with each other due to
differential refraction in the air colummn thru which the light passes.
This forms the basis for the 'speckle interferometry' image reconstruction
technique in which a grossly enlarged intensified short exposure image
of a star is scanned and individual sub images extracted and added together
to get something approximating the image one gets at the diffraction
limit.






Andy Saulietis / DTG Alt-Az-Fp Drive Systems
HDPE Worm Gears, Custom designs & Machine work
12617 Harriet Ln
Santa Fe, TX 77510 USA
409-925-8854 Voice/Fax
e-mail: andydtg@phoenix.net