  In this paper we present and analyze new CCD $UBVRI$ photometry down to $V
\approx$ 21 in the region of the young open cluster Collinder 232, located in
the Carina spiral arm, and discuss its relationship to Trumpler 14 and Trumpler
16, the two most prominent young open clusters located in the core of NGC 3372
(the Carina Nebula). First of all we study the extinction pattern in the
region. We find that the total to selective absorption ratio $R_V$ differs from
cluster to cluster, being $3.48\pm0.11$, $4.16\pm0.07$ and $3.73\pm0.01$ for
Trumpler 16, Trumpler 14 and Collinder 232, respectively. Then we derive
individual reddenings and intrinsic colours and magnitudes using the method
devised by Romaniello et al. (2002). Ages, age spreads and distances are then
estimated by comparing the Colour Magnitude Diagrams and the Hertzsprung-Russel
diagram with post and pre-main sequence tracks and isochrones. We find that
Trumpler 14 and Collinder 232 lie at the same distance from the Sun (about 2.5
kpc), whereas Trumpler 16 lies much further out, at about 4 kpc from the Sun.
As for the age, we find that Trumpler 16 is older than both Trumpler 14 and
Collinder 232. For all the clusters we indicate the existence of a significant
age dispersion, whose precise value is hampered by our inability to properly
distinguish members from non-members. We finally suggest that Collinder 232 is
a physical aggregate and provide estimates of its basic parameters.
