And testing the guiding I tried 10 min subs. It is very well. It is too much time to Canon. The luminance of stars are something over-exposed.
GSO 305 mm - Canon Rebel XT - ISO 100 - 1 hour 10 min - 7 x 10 min - OAG - DSI-1 - Cor. Coma
large scale:
http://cdn.astrobin.com/images/3e2de...61addad534.jpg
Detail in large scale:
http://cdn.astrobin.com/images/34e4e...b07429d7d0.jpg