  This paper describes the automatic measurement of the spatial organization of
the visual axes of insect compound eyes, which consist of several thousands of
visual units called ommatidia. Each ommatidium samples the optical information
from a small solid angle, with an approximately Gaussian-distributed
sensitivity (half-width of the order of one degree) centered around a visual
axis. Together, the ommatidia gather the optical information from virtually the
full surroundings. The spatial distribution of the visual axes thus determines
the eye's spatial resolution. Knowledge of the optical organization of a
compound eye and its visual acuity is crucial for quantitative studies of the
neural processing of visual information. Here we present an automated procedure
for mapping a compound eye's visual axes, using an intrinsic optical
phenomenon, the pseudopupil. We outline the optomechanical setup for scanning
insect eyes, and use experimental results obtained from a housefly, Musca
domestica, to illustrate the steps in the measurement procedure.
