Hemispherical canopy photography involves taking photographs through a hemispherical (fisheye) lens pointed upward from beneath a plant canopy. The resulting photographs can be analyzed to determine the geometry of canopy openings and to calculate potential light penetration. This manual serves as a comprehensive guide to the program CANOPY, a public domain microcomputer program for image analysis of hemispherical canopy photography. Included are discussions of theory, research applications, field methodology, hardware setup and operation, and software setup and operation. CANOPY enables video digitization of negatives, real-time display of positive images, interactive determination of a threshold to distinguish foliage from canopy openings, editing of photographs with poor exposure, rapid calculation of various measures of canopy geometry and indices of potential light penetration, and convenient output of results. A series of utility programs allow user specification of theoretical or empirical distributions of direct sunlight and diffuse skylight for a given site. _____________________________________ CHAPTER