The Rubin LSST telescope, with its deep filters (ugrizy) and the multi-band information, will provide us with the ability to extract complete catalogues of young stellar object populations and to study their peculiar physical processes.As a precursor for Rubin LSST, we will present DECam data of Carina Nebula star forming region, relevant for both star forming region investigation and for source extraction in a crowded field. In particular, we will discuss the main issues related to the analysis of such fields, using an instrument very similar to Rubin LSST. This will be useful as a guide to also extract reliable sources and do photometry in star forming regions or in crowded fields in general.After introducing the whole DECam multi-band survey of the Carina Nebula, this talk will focus on our goal to obtain a complete and detailed stellar catalogue of Carina Nebula in the '2' band. We will discuss our approach and highlight its significance in the context of future Rubin LSST data (that will need to be studied in the same way), and we will show how we can use the Rubin Science Platform as an instrument for visual representation of these data.