The Canon EF 100-400mm f4.5-5.6L IS lens is the lens I would keep if I could
only have one. It is not quite as sharp as the 400 prime but the other
advantages are of greater value to me. It focus's at 6' compared to almost
12' for the prime. It's surprising the number of times I've used the close
focusing setting. Being able to sit quietly and wait as Jim Rosso suggests
is a natural with the 100-400 zoom and the IS for handholding, although if
possible I still prefer to use a tripod.
I started with a 70-300 IS and quickly went up to the 100-400 for distance
and quality. I now mostly use a 500mm f4 and I love it, but like I said if I
could have only one it would be the 100-400.

Joseph Higbee
Spanaway, WA
Mailto: jvhigbee at hotmail.com