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Image aberrations in interferometers

Optical designs for phased-array imaging telescopes, and for interferometers with sparsely filled apertures, using simple two-mirror subtelescopes are discussed. Limitations to the field of view caused by Petzval curvature and distortion are discussed. Methods for reducing or correcting Petzval curvature in these systems by the use of off-axis paraboloidal mirrors are presented and design examples are given. It is shown that a 2.4 times increase in the field of view is possible for 10m diameter arrays, but that residual distortion precludes application of the method to the 50m diameter interferometers considered.