I have used Nikon 6T diopters a lot in the past - very good quality for the amount you shell out.. available in 62 mm dia only if I recall correctly.

However, I find more flexibility with extension tubes, particularly when I use it on telephoto lenses - can be used to isolate a bit distant objects even better and create a nice dreamy feel. One of my shots with an extension tube on a cheapo zoom lens can be seen here http://www.flickr.com/photos/a_peek_...ld/2379621071/

Hope this helps.

Cheers
Deb