of CFBDS; i.e., each $\sim$ 1 square degree MegaCam field is covered by nine 21’ by 21’ WIRCam $J$-band 45-second exposures. For the sake of efficiency, no dithering is done. Instead, the 9 adjacent fields observed in sequence are used for sky construction. Each 9-field patch is actually observed twice, generally one night apart, in order to identify and remove any moving solar system object, for a total integration time of 90 seconds. The second sequence is observed with few pixels offset to average the fixed noise pattern seen on the WIRCam detectors. The 10$\sigma$ limiting depth of $J_{vega}=20.0$ ensures that all confirmed ultracool brown dwarf candidates can be observed with low-resolution spectrographs on 8-meter class telescopes.\
[**Optical data.**]{} The optical data consist of the $z'$-band images used for the CFBD Survey. This survey is made of public and P.I. data and associated 4 sub-surveys of different area shallowness, namely the Canada-France-Hawaii Telescope Legacy Survey-Very Wide,CFHTLS-Wide, CFHTLS-Deep and Red-sequence Cluster Survey-2 (RCS2), described in detail by @Delorme.2008b. The CFBDSIR only targets the 3 shallower components, as shown in Table \[maglim\]. This table compares the limiting magnitude, the maximum distances of detection for mid-L, mid T and the latest T-dwarfs, together 