The luminosity function of MS2255.7+2039 at z = 0.288 is determined down to a total magnitude of R \sim 24 , corresponding to M _ { \mbox { \tiny { R } } } \sim - 17 ( { H } _ { \mbox { \tiny { 0 } } } = 50 { km s } ^ { -1 % } { Mpc } ^ { -1 } ) .
The data are corrected for incompleteness and crowding using detailed simulations .
We find that the luminosity function is steeper than a standard Schechter function at faint magnitudes , and shows an excess of galaxies below M _ { \mbox { \tiny { R } } } \sim - 19 .
After corrections for light loss and crowding , the data can be described by a sum of two Schechter functions , one with M _ { \mbox { \tiny { R } } } ^ { * } = -22.8 and \alpha = -1.0 , and one steeper with M _ { \mbox { \tiny { R } } } ^ { * } = -18.9 and \alpha = -1.5 , representing the dwarf population .
A straight-line fit to the faint part yields a slope similar to the Schechter \alpha = -1.5 of the dwarf population .
The luminosity function of MS2255.7+2039 is compared to other clusters at lower redshifts , and does not show any significant difference .
The redshift range for clusters in which increased number of dwarf galaxies have been found is therefore extended to higher redshifts .