Hey,
Been chasing dragonflies of late. The 100-400L has proved to be a good lens for it, more useful that 100mm macro anyways. It would be good, though to reduce the 1.8m minimum focus distance.
Anybody had any luck using the 100-400 on extension tubes for insect photography?
Cheers!
http://www.pbase.com/thecellartroll/mini_beasts