Recently I played around a little bit with simple lenses mounted on a SLR using a body cap and macro bellows. First the setup using the convex lens of a cheap magnifiying glass and a Cokin filter holder as lens board and aperture holder.
And a few sample pictures.
Full open aperture f/2.4 (Canon EOS 300, Lucky SHD 100, Calbe R09)
Aperture f/4 (Canon EOS 300, Lucky SHD 100, Calbe R09)
Canon EOS 500D, f/4
Canon EOS 500D, f/2.4
Canon EOS 500D, f/8.3 (with smaller apertures this lens is pretty sharp)
More pictures in this flickr set: www.flickr.com/photos/ren-on/sets/72157624886206060/