16-35mm f2.8 L or 17-40mm L fast focusing...

[Belle&Sebastain]

Go read one by one folks. I've done my time, no point continuing saying again n again!

a few people agree with me, we are not getting any answers to your claim at all. How does a bigger barrel affect focusing speed?

how did you measure the barrel of 50mm 1.4 and the barrel of 16-35mm 2.8 is state that they are similar?

 

[songandesther]

Currently I've both lens but I've never thought of comparing their focusing speed. The main factors you will choose between them are f2.8 and price and not focusing speed. Besides, when AF is not invented yet, people still take stunning pictures.

 

[freelancer]

My personal view: in really low light, the 50/1.4 should focus a LOT more accurately than the 16-35. SHOULD, but not MUST. In daylight etc, the 16-35 MAY focus a lot faster, knowing that the USM is Ring type, and not MicroUSM type.

How accurate a camera AF is dependent on the AF processing chip and associated components. How accurate a lens can move the focus "ring" is dependent on the lens design.

For discussion purposes try taking a 50/1.8 lens and take a series of shots, repeating each time by setting the focus to infinity. I can guarantee you that you will find the focus point shifting to an extent. Try the same with a 85/1.8 lens and its spot on everytime. I know this because I had tested this with a 20D centre point, tripod mounted with cable release.

This tells you that the lens design is the cause of how accurate the AF motor in the lens will move for a given signal from the camera's AF system. I know I am simplifying things a little here but would like to correct some of the points posted

 

[Castlesinthesky]

I've used the 17-40 on my EOS 30 and AF is rather fast too. All my shots using this lens are indoors and performance is impressive.

In your point, the 16-35 being faster than the 50 f/1.4 is not only due to the Ring USM on the 16-35, but must also consider the barrel size.

:bsmilie: Are you sure?i do my work all the time in extreme low light at F4 and i still focus very fast.i'm using a lowly 20d somemore.

 

[EUGSEOW]

I had 17-40mm f/4L and have 16-35mm f/2.8L.

In terms of sharpness, I couldnt really tell even viewing at 100% at equivalent focal length. I sold the 17-40mm for 16-35mm becoz I need the versatility of fast f/2.8.

16-35mm also focuses faster on my 1D.