We present high-speed , multicolour photometry of the faint , eclipsing cataclysmic variable ( CV ) SDSS J105754.25+275947.5 .
The light from this system is dominated by the white dwarf .
Nonetheless , averaging many eclipses reveals additional features from the eclipse of the bright spot .
This enables the fitting of a parameterised eclipse model to these average light curves , allowing the precise measurement of system parameters .
We find a mass ratio of q = 0.0546 \pm 0.0020 and inclination i = 85.74 \pm 0.21 ^ { \circ } .
The white dwarf and donor masses were found to be M _ { \mathrm { w } } = 0.800 \pm 0.015 M _ { \odot } and M _ { \mathrm { d } } = 0.0436 \pm 0.0020 M _ { \odot } , respectively .
A temperature T _ { \mathrm { w } } = 13300 \pm 1100 K and distance d = 367 \pm 26 pc of the white dwarf were estimated through fitting model atmosphere predictions to multicolour fluxes .
The mass of the white dwarf in SDSS 105754.25+275947.5 is close to the average for CV white dwarfs , while the donor has the lowest mass yet measured in an eclipsing CV .
A low-mass donor and an orbital period ( 90.44 min ) significantly longer than the period minimum strongly suggest that this is a bona fide period-bounce system , although formation from a white dwarf/brown dwarf binary can not be ruled out .
Very few period-minimum/period-bounce systems with precise system parameters are currently known , and as a consequence the evolution of CVs in this regime is not yet fully understood .