A simple three-element eyepiece is presented which has a zero Petzval sum and is corrected for both longitudinal and lateral color. Following a third-order analysis, results of ray tracing several examples are presented. Designs using a single glass are useful at ƒ/4 and 40°, and multiglass designs can be used at ƒ/3 and 40°. These latter designs also correct the coma of a paraboloidal mirror objective.
Thomas L. Clarke, "Simple flat-field eyepiece," Appl. Opt. 22, 1807-1811 (1983)