  We present the results of a deep optical 2.6 square degree survey with near
infrared follow-up measurements of the intermediate-aged Praesepe open cluster.
The survey is complete to I=21.3, Z=20.5, corresponding to ~0.06 Solar Masses
assuming a cluster age of 0.5 Gyrs. Using 3-5 pass-bands to constrain cluster
membership, we identify 32 new low mass cluster members, at least 4 of which
are likely to be substellar. We use the low mass census to trace the region
where the sequence moves away from the NEXTGEN towards the Dusty regime at Teff
= 2200K. In doing so, we identify four unresolved binaries, yielding a
substellar binary fraction of ~30 percent. The binary fractions appear to
decrease below 0.1 Solar Masses, in contrast to the rising fractions found in
the Pleiades. We also identify a paucity of late M dwarfs, thought to be due to
a steepening in the mass-luminosity relation at these spectral types, and
compare the properties of this gap in the sequence to those observed in younger
clusters. We note an overdensity of faint sources in the region of the
so-called subcluster (possibly an older smaller cluster within Praesepe), and
subsequently derive the luminosity and mass functions for the main Praesepe
cluster, revealing a turn-over near the substellar boundary. We conclude by
presenting astrometric measurements for low mass Praesepe candidates from the
literature, and rule out as a likely foreground dwarf RPr1, hitherto thought to
be a substellar member.
