Balancing the astigmatic fields when all other aberrations are absent.
When all aberrations are absent other than third-order astigmatism and Petzval, it is demonstrated that selection of a flat tangential astigmatic field is optimum if the smallest maximum spot size is desired over the entire field of view. With balanced sagittal and tangential fields the spot size is observed to be smaller than the flat-tangential-field case until the field angle reaches √? of the full-field angle. Comparisons of the spot sizes and shapes for these cases and the flat-sagittal-field case are made for flat and optimally curved image surfaces.
Johnson
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RB