  We performed a HST/WFC3-IR imaging survey of the young stellar cluster NGC
2024 in three filters probing the 1.4~$\mu$m H$_2$O absorption feature,
characteristic of the population of low mass and sub-stellar mass objects down
to a few Jupyter masses. We detect 812 point sources, 550 of them in all 3
filters with signal to noise greater than 5. Using a distance-independent
two-color diagram we determine extinction values as high as $A_V\simeq 40$. We
also find that the change of effective wavelengths in our filters results in
higher $A_V$ values as the reddening increases. Reconstructing a dereddened
color-magnitude diagram we derive a luminosity histogram for both the full
sample of candidate cluster members and for an extinction-limited sub-sample
containing the 50% of sources with $A_V\lesssim 15$. Assuming a standard
extinction law like Cardelli et al. (1989) with a nominal $R_V$=3.1 we produce
a luminosity function in good agreement with the one resulting from a
Salpeter-like Initial Mass Function for a 1~Myr isochrone. There is some
evidence of an excess of luminous stars in the most embedded region. We posit
that the correlation may be due to those sources being younger, and therefore
overluminous than the more evolved and less extinct cluster's stars. We compare
our classification scheme based on the depth of the 1.4$\mu$m photometric
feature with the results from the spectroscopic survey of Levine et al. (2006),
and we report a few peculiar sources and morphological features typical of the
rich phenomenology commonly encountered in young star-forming regions.
