Selection effects as a function of J–band magnitude across different stages of the sample construction. For this plot, we removed the southern part of the field (δ < 66.8°). Top: Fraction of objects surviving the main selection step (PRF classification). Middle: Percentage of objects remaining at each magnitude step relative to the sample of probable members from the PRF run. The orange symbols show the percentage of surviving objects after removing the objects older than 30 Myr (Section. 4.2), and the gray symbols show those with valid mass estimates (Section. 6.1). Bottom: Same as the middle panel, but showing the number of objects instead of percentages. Tick marks on the top x-axis indicate approximate stellar masses corresponding to J–band magnitudes at the distance of Berkeley 59, age of 2 Myr and extinction A_V = 4 mag.