  In this paper we describe weighting techniques used for the optimal
coaddition of CCD frames with differing characteristics. Optimal means maximum
signal-to-noise (s/n) for stellar objects. We derive formulae for four
applications: 1) object detection via matched filter, 2) object detection
identical to DAOFIND, 3) aperture photometry, and 4) ALLSTAR profile-fitting
photometry. We have included examples involving 21 frames for which either the
sky brightness or image resolution varied by a factor of three. The gains in
s/n were modest for most of the examples, except for DAOFIND detection with
varying image resolution which exhibited a substantial s/n increase. Even
though the only consideration was maximizing s/n, the image resolution was seen
to improve for most of the variable resolution examples. Also discussed are
empirical fits for the weighting and the availability of the program, WEIGHT,
used to generate the weighting for the individual frames. Finally, we include
appendices describing the effects of clipping algorithms and a scheme for
star/galaxy and cosmic ray/star discrimination.
