  Two-dimensional surface photometry has been done for 166 {\em early-type}
galaxies (bulge/total luminosity $B/T>0.6$) in 3 fields of the Canadian Network
for Observational Cosmology (CNOC) cluster survey. These galaxies are either
spectroscopically confirmed members of clusters at $z=0.23$ (45 galaxies),
$0.43$ (22), and $0.55$ (16) or field galaxies in the same redshift range. An
additional 51 early-type galaxies in the rich cluster Abell 2256 at $z=0.06$
were analysed with the same technique. The resulting structural and surface
brightness measurements show that, in the plane of absolute magnitude
$M_{AB}(B)$ versus $\log R_e$ (half-light radius), the locus of cluster
ellipticals shifts monotonically with redshift so that at redshifts of (0.23,
0.43, 0.55), galaxies of a given size are more luminous by ($-0.25\pm
0.10,-0.55\pm 0.12,-0.74\pm 0.21$) magnitudes with respect to the same relation
measured at $z=0.06$ (adopting $q_\circ=0.5$). There is no evidence that
early-type galaxies in the field evolve differently from those in clusters. If
dynamical processes do not substantially modify the size-luminosity relation
for early-type galaxies over the observed redshift range, then these galaxies
have undergone significant luminosity evolution over the past half of the age
of the universe. The amount of brightening is consistent with passive evolution
models of old, single-burst stellar populations.
