Huh then something's VERY VERY wrong w your gear or w your skills!! If you use the AF switch limiter the 1-400 IS is quite snappy and tracks very very easy on a 40d! I can even track incoming (head on) seagulls w it..and that's a hard 1 for both the lens and the AF system!! Even fast flying ducks are a piece of cake w the 40d + 1-400 IS! Gosh I've been tracking cormorants IF even w a XT+70-300 IS!!
For the OP....i'm w Tony (Imagemaster) here!
It maybe my camera, as the lens tracks ok, but in AI servo 75% of the time is front focussed. In one shot the focus is dead on. If you can explain how it's fine in one shot and hopeless in AI servo I'm all ears.
I had a Bigma for a while and sold it because it wouldn't lock focus fast enough even for larger slower moving birds like Trumpeter Swans or Sandhill Cranes. That being said Servo on my 40D is not its strong point. Since the Bigma I have aquired the 100-400, 400 f 5.6 and 300 f 2.8. I noticed an immediate improvement with the 100-400 and 400 f 5.6. There was not as much difference between the two in locking focus speed especially with the IS on the 100-400 turned off. I can't say enough about the 300 f 2.8 but when using it with a 2X TC the Servo focus would not keep up on my 40D. This is not the case on my 50D where it keeps up just fine as something in the 50D focus has apparently been tweaked. IMHO the 40D is marginal for faster BIF with one of the Canon lenses listed above and near impossible with a Bigma. If you are serious about BIF I would sell the Bigma and get something better.
This is coming out of left field, but I noticed when I got my 40D that it absolutely falls apart when I tricked it into using an f/8 lens combo (ie: 100-400+1.4x or 300/2.8 + "2.8x"). AF simply doesn't work. Even in the clear noon day sun. As soon as I went back to f/5.6, the lenses worked great. By contrast, my 5D simply got a somewhat worse at f/8 (as you might see from f/4 to f/5.6), and even my 350D was somewhat usable at f/5.6.
I've heard others claim that when moving from a 30D to 40D they noticed their AF performance with a taped 1.4x TC (giving f/8) got much worse. I believe the general conclusion is that while other bodies seemed to work fine at f/8 if tricked, the 40D has some unknown trait that absolutely kills its performance, so you might as well not try AF.
Perhaps the Bigma (which is f/6.3 at 500mm) suffers "early onset" of this phenomena? Perhaps it might work better if you dialed back the focal length to the point where the lens is actually f/5.6?
CKrueger wrote:
This is coming out of left field, but I noticed when I got my 40D that it absolutely falls apart when I tricked it into using an f/8 lens combo (ie: 100-400+1.4x or 300/2.8 + "2.8x"). AF simply doesn't work. Even in the clear noon day sun. As soon as I went back to f/5.6, the lenses worked great. By contrast, my 5D simply got a somewhat worse at f/8 (as you might see from f/4 to f/5.6), and even my 350D was somewhat usable at f/5.6.
I've heard others claim that when moving from a 30D to 40D they noticed their AF performance with a taped 1.4x TC (giving f/8) got much worse. I believe the general conclusion is that while other bodies seemed to work fine at f/8 if tricked, the 40D has some unknown trait that absolutely kills its performance, so you might as well not try AF.
Perhaps the Bigma (which is f/6.3 at 500mm) suffers "early onset" of this phenomena? Perhaps it might work better if you dialed back the focal length to the point where the lens is actually f/5.6?
Something to consider, anyway.......Show more →
Thanks for the input. I believe this is possible alright. The Bigma itself ( my copy ) seems to be a poor performer at 500 mm unless I am using it to shoot slow moving objects or inanimate objects. I do not mean the optics are bad. Actually at 200 mm , it compares nicely to my 70-200 f 2.8 IS . I will continue to practice with this combination until I can afford a new lens. I will be looking for a 400 5.6 prime. But for now I will try to remember to keep the focal length close to 300 and 400 mm on the Bigma while in AI Servo.
