  The number of type Ia supernova observations will see a significant growth
within the next decade, especially thanks to the Legacy Survey of Space and
Time undertaken by the Vera Rubin Observatory in Chile. With this rise, the
statistical uncertainties will decrease and the flux calibration will become
the main uncertainty for the characterization of dark energy. The uncertainty
over the telescope transmission is a major systematic when measuring SNe Ia
colors. Here we introduce the Collimated Beam Projector (CBP), a device that
can measure the transmission of a telescope and its filters. Composed of a
tunable monochromatic light source and optics to provide a parallel output beam
this device is able to measure with high precision the filter transmissions. In
the following, we will show how measuring precisely a telescope transmission
can also improve the precision of the dark energy parameters. As an example, we
will present the first results of the CBP in the context of the StarDice
experiment.
