  We identify new Y- and T-type brown dwarfs from the WISE All Sky data release
using images obtained in filters that divide the traditional near-infrared H
and J bands into two halves -- specifically CH4s & CH4l in the H and J2 & J3 in
the J. This proves to be very effective at identifying cool brown dwarfs via
the detection of their methane absorption, as well as providing preliminary
classification using methane colours and WISE-to-near-infrared colours. New and
updated calibrations between T/Y spectral types and CH4s-CH4l, J3-W2, and
CH4s-W2 colours are derived, producing classification estimates good to a few
spectral sub-types. We present photometry for a large sample of T and Y dwarfs
in these filters, together with spectroscopy for 23 new ultra-cool dwarfs - two
Y dwarfs and twenty one T dwarfs. We identify a further 8 new cool brown
dwarfs, which we have high confidence are T dwarfs based on their methane
photometry. We find that, for objects observed on a 4m-class telescope at J
band magnitudes of ~20 or brighter, CH4s-CH4l is the more powerful colour for
detecting objects and then estimating spectral types. Due to the lower sky
background in the J-band, the J3 and J2 bands are more useful for identifying
fainter cool dwarfs at J>22. The J3-J2 colour is poor at estimating spectral
types. But fortunately, once J3-J2 confirms that an object is a cool dwarf, the
J3-W2 colour is very effective at estimating approximate spectral types.
