M51 - the whirlpool galaxy
This galaxy is in the constellation of Canes Venatici, but only just a short distance from the end star of the handle of Ursa Major. It is a fine spiral, about 25 million light years away. It is interacting with (has collided with?) another small elliptical galaxy that can be seen at the end of one of the arms, at the top of the photo.
This page shows a comparison between taking images at prime focus or with Barlow 2x magnification. The first image is the Barlow one, which clearly shows more detail but needs more frames to reduce noise.
Canon EOS5DMkII 254mm Newtonian @ 2380mm 100 x 20s f/9.4 ISO6400 2010-04-07 21:12:18-21:54:21 UT
Canon EOS5DMkII 254mm Newtonian @ 1200mm 100 x 10s f/4.8 ISO3200 2010-04-04 21:20:05-21:45:09 UT