Blazars are a category of active galactic nuclei that feature the emission of a jet pointing to the observer. We are performing a photometric measurement aimed at studying a possible variation of the jet: depending on the observed variations, one could discriminate among various models describing the mechanism of the jet emission.
Preliminary results have been shown at a conference in 2015 and published in the conference proceedings and reported in the master degree thesis of Chiara Righi. As an example we show the observation of a candidate blazar of magnitude 20.3 along with the reference stars to be used for the differential photometry: even if very faint, the object could be isolated from the background with a large significance.