$\star$ Cut field reduced

For the measurement of our supernovæ, we use Planetary Camera. It is one of the 4 CCDs of the WFPC2, and it has the finest pixelisation: a pixel covers a surface of one twentieth of arc second square on the sky, and it covers on the whole $40' ' \times 40' '$.

It is thus very difficult to use the little of objects present in the field to make the alignment of the images a posteriori . One needs for the moment observations to keep the same one pointed between the various installations of the field. The principal disadvantage is that the dead zones of the CCD will be present at the same place on the sky and could not thus be eliminated during the image processing: this forces to position the object which one wants to measure flux in a zone of the detector far from any cosmetic defect.