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I'm not sure exactly why they say its not diffrection limited. My design has a max RMS wavefront error about 0.09 micron over a 200 mm diameter.
Its less than 0.03 micron over a 100 mm diameter fileld. But they are using Strehl ratio of 0.8 as criterion. That probably means that they are including things like surface roughness (I think they quote 38 nm typical value),
figure errors (unspecified) , the impossibility of spending forever tweeking the mirror positions, plus diffraction due to the spokes and the hexagon separations. Adding all that up say 0.07 micron and
.12 micron for the two fields. You multiply by 12 to get the wavelength for
a Strehl ratio of 0.8. This gives about 0.84 micron and 1.44 micron
the the diffraction limited wavelength for the two field sizes's edges.
That's reasonably close to their spec of 2 microns.
Given that the thing has lots of edge differaction problems, its
gonna give images for stars that look awful.
The various detection devices are fixed in the fields, with the
longer wavelength spectrometers in the outermost areas. The images of
galaxies with the shortest wave imager will look nice.
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