High-aperture beams: comment.
Clarifications are provided for the proper choice of the branch of a square-root function that is connected with the singularity on the focal plane occurring in the treatment by Sheppard on 'High-aperture beams' [J. Opt. Soc. Am. A18, 1579 (2001)]. The author's claim that the singularity is nonphysical is disputed.
Seshadri
S R
SR
s.r.seshadri@osa.org