OpticsPosted by Peter Thejll Sun, November 10, 2013 12:16:52
It is probably necessary to have that SKE - it leaves a remnant halo, but the intensity of this is very much lower than the halo you get with our co-add technique. Our SKE never worked and I wonder how a potential future one could be constructed?
One alternative could be these 'Digital Mirror Devices (DMDs)' which are essentially a adressable semiconductor matrix of little mirrors. The whole things is like a CCD in size but each element can be tipped to one side or the other, thus deflecting light. If one of those devices sat in the prime focus of an objective we could first take an image of the Moon, find the pixels that needed their light deflected, and then address those only and send their light off to one side, thus obtaining a sort of dynamic SKE. Mechanical SKEs still have to be positioned, which I think caused the death of our system - too many motors with dodgy systems for measuring the turning angle, timeouts that never got their timeout and so on.
A DMD array could be fixed in place and operated with software only. Apparently DMDs are evolving fast and in 2014 some kits for experimenting, by Texas Instruments, will come out. The Kits are supposedly some hundreds of dollars.
They need to be driven by something, and here is a driver board (for $210):
We need to get one of these - with some small pot of money to be raised by sale of stuff from the MLO system (when we decide to do that) - or a small proposal.
Such a DMD undoubtedly has its own PSF and that needs to be tested.
The DMDs have a 'fill factor' of about 90% - so an issue is what happens to the remaining 10%. Is it diffusely scattered or is it cast in another direction? Apparently there are three states to a MDD picel - left, off and right, where the left and right states position the light at +/- 14 degrees. The Offs tate is to be understood.
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