Photometry differential of comets
  Here are presented the results obtained with three comets 73P (Schwassmann Wachmann) B the component B, 6P dArrest and C2008 J1 (Boattini). Comet 73P was observed in April 2006 with a CCD camera Starlight Express SXL8 attached to direct focus of a Newton telescope 250 mm, focal length 1200 mm, while the 6P and C2008 J1 were ever observed by telescope Newtonian but with a CCD camera Atik 16IC to direct focus. To the CCD camera was added a filter photometric Rc (Schuler). For 6P comet has been used a defocus of 14 pixels, meaning that the central false nucleus has defocused a FWHM of 14 pixels. The technical data of the tools used are shown in Tables 1 and 2. 
Toni Scarmato
astro-ph.SR astro-ph.EP