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 \pm 0.11 , 4.16 \pm 0.07 and 3.73 \pm 0.01 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 .