We present the photometric calibration technique for the Digitized Second
Palomar Observatory Sky Survey (DPOSS), used to create seamless catalogs of
calibrated objects over large sky areas. After applying a correction for
telescope vignetting, the extensive plate overlap regions are used to transform
sets of plates onto a common instrumental photometric system. Photometric
transformations to the Gunn gri system for each plate, for stars and galaxies,
are derived using these contiguous stitched areas and an extensive CCD imaging
library obtained for this purpose. We discuss the resulting photometric
accuracy, survey depth, and possible systematic errors.Comment: 25 pages, 13 figures. Accepted to AJ. Some figures shrunk or missing
to limit file size; the full paper is available at
http://www.sdss.jhu.edu/~rrg/science/papers/photometrypaper.ps.g
