70-300IS vs 300f4LIS servo AF speed on 20D?

[dariusz calkowski]

Hello. My question is how much better is AF in tracking mode with 300f4LIS VS

my 70-300IS on 20D body. Will I get much more keepers? If now I can get 10%

sharp pictures will I get 20% or 50%? Is it night and day? Or should I get 1d

body(no chance with my funds). Second question is how does it(300f4) in servo

with 1.4 converter? Third question:Is possible to use 70-300 with tamron or

kenko tc and get AF? I read various opinions, some said yes, some said that it

hunts on 20D. If yes what about servo? I dont think it works but mayby... Thank

you for your help.

[david_lau3]

I have the 300/f4 and the 75-300IS (previous version of 70-300IS). The 300/f4 focus much faster than the 75-300, due to its ring type USM (75-300 is micro USM only). The 70-300 also has the same micro USM motor as the 75-300, and should be as slow (or fast).

 

How bad it servo against 300/f4 depends on the subject movement and direction.

 

300/f4 will focus slower with Canon 1.4X, which is by design to get better focus accuracy. I am not sure it is faster with 3rd party 1.4X.

 

For 70-300 with 3rd party 1.4X, even you can fool the camera with tape etc, the focus speed and accuracy are still much in doubt.

[bobatkins]

The 300/4L is much better at focus tracking.

 

I use MF with a 1.4x on the 70-300IS. AF is poor with a TC added.

[ron_kunzelman]

Bob,

 

Which model of 1.4TC are you using with your 70-300IS?

[jimstrutz]

I sometimes use a Kenko 1.5x TC with the 70-300IS. On a 20D the focus is indeed poor. It seems to work well enough at the short end of the zoom, but what's the point in that? At the long end it will only lock on if there is enough light and contrast, but it's pretty erratic. Bob's right that MF is easier to deal with. Interestingly, I find it considerably better at autofocusing on a 10D and the original DRebel. Still not great, but better. Image quaility also suffers with a TC. It's still usable, but...