I have a Sigma 120-400 and access to a 100-400 at work. The Sigma beats the Canon.... this has to be putting pressure on Canon to upgrade it.
Don, can you elaborate on the Sigma vs Canon comparison??? If I tire of waiting for the "new" 100-400 I might buy the Sigma. I was never quite happy w/the 100-400 and sold it, still rent one now and then. The reviews I read of the two Sigmas (120-400, 120-500) werent' great. Tx.
My test was not very scientific, only one copy of each lens, plus a Sigma 150-500 and a Canon 400 5.6....
The setup was a tripod mount, outdoors on a clear sunny day, and the target was cars on the other side of the parking lot. I can't remember what the shutter speed was, but it was ISO800, fastest F stop, and the body was a 60D. All lenses were manually focused with live view, zoomed in all the way. Shutter was 10 second delay so any vibrations would hopefully be dampened out. Image evaluation was by using the rear display to zoom in on a selected area of the picture, a car licence plate at the center of the picture.
Canon 100-400 at 400 5.6, could barely read liscence plate
Sigma 120-400 at 400 5.6, could read plate
Sigma 150-500 at 500 6.3, could not read plate
Canon 400 at 5.6, plate was very readable
I had expected the Canon 400 to be the best, and no suprise there. I expected the Canon 100-400 to be better than the Sigma 120-400 so I was suprised to find otherwise. I had also expected that the longer range of the Sigma 150-500 would resolve better than the shorter 120-400 so I was very suprised to find otherwise