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

[syke]

ditto B&S.. i would like to know too.

I think he replaced aperture size with barrel size.

 

[Snoweagle]

pardon my newbieness, what has barrel size got to do with focussing speed, please enlighten me:angel:

Larger barrel size + large aperture + USM = faster AF

 

[Snoweagle]

I think he replaced aperture size with barrel size.

Nope, no misplacements.

 

[syke]

Nope, no misplacements.

Do you have anything on it I can read up on.

This reminds me of what my boss always say, the only 2 things he has complete trust in, god and data.

 

[sweat100]

Barrell size? I am not sure about that.:dunno:
Also at low light, the contrast of the scene invariably lowers so makes it harder to AF.

 

[Snoweagle]

Do you have anything on it I can read up on.

This reminds me of what my boss always say, the only 2 things he has complete trust in, god and data.

A larger lens barrel allows more light to enter. Here's an article talking about fast lens.

http://medfmt.8k.com/mf/fast.html

 

[Snoweagle]

Barrell size? I am not sure about that.:dunno:
Also at low light, the contrast of the scene invariably lowers so makes it harder to AF.

Yes true, cos not enough light is present to assist AF.

 

[LeaderXXX]

Is tat mean 50mm f1.8 maybe focusing faster den 16-35mm f2.8 if shooting in disco etc??Which have more chances OOF/miss F??

 

[Belle&Sebastain]

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.

Larger barrel size + large aperture + USM = faster AF

the 2 post does not make sense.

first post 18, you said barrel size makes focusing slower because being a 50mm 1.4, the barrel is larger

now post 22, you said large barrel size + large aperture + USM = aperture by your accounts 50mm 1.4 should focus faster than 16-35 because by your OWN theroy 50mm barrel size is larger, has a larger aperture size with USM.

so have you own the 16-35mm or 50mm 1.4?

which is faster?

Why are you so contridicting?
:devil:

 

[Belle&Sebastain]

Yes true, cos not enough light is present to assist AF.

this does not telly with post 18 which you said a 16-35mm 2.8 focus faster then 50mm 1.4. cos there is not as much light entering the 16-35 (less by 2 stops) to the 50mm.

 

[Tsangstudios]

I have owned both lenses and both are equivilantly fast.. Both use USM the 16 may be just marginally faster cause its has a slightly less range to hunt over. But in partical photogrpahy it wont make any difference

 

[freelancer]

Correct, usually i'll use the 2.8 end when i'm only taking portraits. Other than that, indoors i'll use f/8.

I try not to take portraits with wides as the distortion on the face can be quite pronounced. With longer lenses it looks nicer plus the bokeh is really sweet ..

 

[Gunbucker]

Do you have anything on it I can read up on.

This reminds me of what my boss always say, the only 2 things he has complete trust in, god and data.

LOL! I also remember that famous quote, I think from some process engineering guru:

"In God we trust. For anything else, bring data."

 

[sweat100]

A larger barrel size will have faster AF should not hold true. Imagine a sigma 24-70mm f2.8 with a filter thread of 82mm while a canon 24-70mm f2.8 with 77mm. This implies that the sigam has a larger barrell than canon. Can the sigma focus faster than the canon? I seriously doubt it. Also the canon 70-200mm f4 with a diameter of 67mm compared to 17-40 f4 with a diameter of 77mm. I think they focus almost the same speed.

After using the 16-35mm f2.8 and 50mm f1.4, i still feel that the 16-35 focus faster like what Tsangstudios said. The 50mm tends to hunt more though it is faster lens.

 

[knneo]

Question:

Ultra fast AF (eg. USM) + High ISO = Ablity capture the subject before it disappear?

Will locked AF be able to do the same thing?

 

[JediForce4ever]

Are you sure? Where did you get that from? :what:

I've tested them side by side before...whether the lenses I have tested are good or bad copies, i do not know.

 

[Discreet]

Personally if you are wondering which lens will AF better in dark situation, I would say the 16-35L... but it is not as though the AF is going twice as good or as fast. In fact, i think both lens "hunts" at the same speed and the 16-35L which allows twice as much light, will give you a higher chance that the camera AF will lock onto.

I used a 17-40L on a rebel and a 24-70L on a 1DmkII and I dont really see that much of an improvement because the places i shoot, the condition is pretty lousy and you really need a F2 or faster lens to focus accurately and quickly. Get a ST-E2 to help you focus or use the focus assist beam on your flash (but disable the main flash gun). It will work MUCH MUCH better

 

[JediForce4ever]

Actually threadstarter, if you really want fast focussing, I'd suggest going for a 1D series body.

 

[Discreet]

The large barrel size theory is wrong.
I have a 85L and a 85/1.8 USM in front of me... and the 85L which has a larger barrel size (72mm vs 58mm) focuses way way slower.

This is what i think is the misconception...

AF speed of the lens (dont care about the body) is dependent on a few things. The most obvious is the motor. Ring USM is faster than Micro USM or Arc Form Motor. Next is the throw of the focusing mechanism. For example, my 85L has a LONG LONG throw. It takes a like a few turns to get from one end to the another. Why is it so long? because at F1.2, you need to be very precise (DOF is thin). If your throw is short, you will miss the focusing.

Also different lens have different focusing distance range. Like my 24-70L does from "macro" to 0.7M to 3M then Infinity. My 70-200L goes from 1.4M to 10M then Infinity.

So if you compare focusing on something that is between 3M and Infinity, my 24-70L(less than 10 deg turn from 3M to Infinity) technically should focus faster than the 70-200L(90 deg turn from 3M to Infinity) because it has such a short range to find focus. So comparing a 50 prime to a 17-40L is like comparing orange and apples. you have to consider how far the subject is and even then the focal length are not the same... how to compare??

I think the OP should consider what kind of situation he is expecting the AF to be slow. Is it within 1M? or at Infinity? or at very close focusing distance (30cm??). It is very subjective but one thing is for sure, the 16-35 will NEVER focus slower. The magic question is it worth the extra $$$?

(IMHO NO, get a ST E2 if you want faster AF at low light condition. If the subject is too far away for the ST E2 to reach, you can focus on infinity using these wide angle zoom anyway)

 

[knneo]

Get a ST-E2 to help you focus or use the focus assist beam on your flash (but disable the main flash gun). It will work MUCH MUCH better

With regards to the above.

How do we disable the the main flash gun when the flash assist is on?