MF of Praesepe based on our survey LBT iz and Ω2k JK_s photometry (triangles), compared with that from Boudreault et al. (2010) (open dots assuming a dusty atmosphere and filled dots assuming a dust-free atmosphere). Error bars are Poissonian arising from the finite number of objects observed in each bin, except for the last bin, for which the error bar is derived from the linear fit. The vertical thin dotted line is the mass limit above which detector saturation occurs in the i and z-bands. The vertical thin long-dashed line is the mass at the 5σ detection limit of our optical LBT data.