Hello, I have compare the image (991101.124)unfilterred with the stars GSC,stars of UsnoSA2.0 and those of the sequence donnee by Hitoshi Yamaoka. Here results: 1)l'Image unfilterred give : 1.1)with 20 stars l'USNO SA2.0 --->SN = 13.47C 1.2)Avec la sequence de H.Yamaoka (mag GSC)---> SN = 14.45C 1.3)Avec 20 stars GSC--->SN=14.50C 2)L'image (991101.112) with Red filter give: 2.1) with 20 stars USNO SA2.0 ---> 13.59Rc 2.2) with GSC04739-0434 (V=12.36 B-V=1.23,U-B=1.15 etR#11.7)(Brian Skiff), ----> SN = 13.53Rc it is seen that the results of sequence H.Y and those of the GSC are practically identical. On the other hand, the estimate magnitude with Usno sa2.0 (13.47C) is nearer to measurements of SN in the image taken with the Red filter. We wish opinions and councils. Thank you Merci Jean Marie Llapasset Obs 635 Perpignan (France) http://perso.wanadoo.fr/jm.llapasset/ http://aude.geoman.net/observation/SN/sn.html (thousand excuses for my English)