|optical design - schmidtcassflat
This page describes a flat-field schmidt-cassegrain optical system.
The radius-of-curvatures of the primary and secondary mirrors produce a flat field without a field lens. Because the center of curvatures of the mirrors are not at the same point, this design is not a classical concentric schmidt-cassegrain. This design intentionally deviates from concentric schmidt cassegrain to produce the flat-field without a field flattener-corrector lens - impossible with concentric schmidts.
The deviation from concentric schmidt-cassegrain introduces some coma and astigmatism, but these aberrations are well compensated for by placing the corrector plate in the optimal position given the selected mirror radii. But the residual coma and astigmatism in this 10" aperture f/4 design are so minor, this optical system is diffraction limited over the intended 2 degree field diameter.
The spots and aberration curves are red because 7065A rays are the last drawn, and this design has virtually zero chromatic aberration. The other colors are therefore drawn over by the final red color.
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spot image wavefront-interference image
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