When a lens is decentered in a microscope objective the most noticeable defect is coma in the center of the field. A method is given for computing the central coma by using the transfer coefficients of M’Aulay and Cruickshank. The results for a typical microscope are given and the experimental means of verification are described.
GLENN WOOTERS, "Lens Centering in Microscope Objectives," J. Opt. Soc. Am. 40, 521-523 (1950)