This article describes a new series of photomicrographic field-flattening eyepieces, designed to compensate the residual aberrations of microscope objectives notably flatness of field and lateral color. The systems are negative in power, and strictly speaking, are not “eyepieces” since the pupil is internal, preventing direct visual use, but they are directly interchangeable with conventional visual eyepieces in the microscope and yield a large and well-corrected image for photomicrography and microprojection.
JAMES R. BENFORD and JOHN V. BUTTERFIELD, "A New Series of Photomicrographic Lenses," J. Opt. Soc. Am. 44, 598-598 (1954)