Composite LBG spectrum from Shapley et al. (2003) shifted to z = 3.631 (black dashed lines) and z = 3.912 (grey solid lines), used for optimising the selection function for the W0410–0913 and W0831+0140 fields, respectively. After accounting for quantum efficiency and atmospheric transmission, the red and blue lines represent the HSC filter curves (used for optimisation and the blank field) and the IMACS filter curves (used for W0410–0913 and W0831+0140), respectively.