135L & 5D AI servo mode

Hi Eden,

I have shot butterflies at even longer distance. The lens is still very sharp and never gave any problem.

Are you using center focus point only (whic is all I use) ? If you let the camera pick AF points, it may be the cause.

Eric.

Eden Yip said:

but my problem appears more evident when shooting at a distance. i
guess, though longer DOF, the focus converges much rapidly at
longer distance, and any minor error in motor movement would induce
significant focus error...

you can see from the pic of my dad... which was taken at F2
one-shot mode.. the lens was able to nail the focus....

have u ever tried 20D to capture moving objects from 15ft or
longer... and AI servo at distant object, e.g. far buildings....

Click to expand...

Eden Yip said:

but my problem appears more evident when shooting at a distance. i
guess, though longer DOF, the focus converges much rapidly at
longer distance, and any minor error in motor movement would induce
significant focus error...

Click to expand...

Eden,

I don't really agree with this. If motor movement ever has a factor here, it will matter more with the shutter speed. The slower, the more blurry. DOF is the thing define what appear in focus and what is not. The shorter the DOF, the harder to get it in focus. The longer focus distance, the more room you have. And the motor movement is consistent. Looking at some of the speed of you photos are at 1/1600 seconds, I don't think motor will be an issue. And none of these should cause a change of focus any way, unless the lens or camera are not calibrated correctly.

Eric.

I dont have the 135 but use the 85 1.8 in low light with the 5D often, always on AI servo. Not always right, but much better results than I got with the lens on the 10D. Same with the 70-200 at f4 with moving objects. I have no joy with using all/auto focus points unless the aperture is shut down

It was f/2.8, and I would estimate the keeper rate at around 70%, which is about as well as any other lens I have on close/fast moving subjects.

Russell
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Eric,

motor movement is not always consistent. i did find my 35L focus much accurate on objects at close distance than anything beyond 15ft, e.g. a advertising panel 100ft away, which is, for a 35mm lens, assumed to infinity. i tested the lens for focusing to distant objects and a considerable nos of shots were OOF. i played the MF ring and found that a little movement at this range could bring the focus from a finite distance to infinity... i suspected the lens was not able to AF consistently.

i sent the lens to canon for service. they canon first said the lens performed compliant with the standards. I insisted him to test it more for distant objects and at the end he confirmed my suspection.... he found that my lens motor frequent was slightly mis-matching with the driving freq... that got the motor once in a while not stopping rite at the desired pos. the canon tech fixed this issues after consultation with their engrs...

Eric Chi said:

Eden,

I don't really agree with this. If motor movement ever has a factor
here, it will matter more with the shutter speed. The slower, the
more blurry. DOF is the thing define what appear in focus and what
is not. The shorter the DOF, the harder to get it in focus. The
longer focus distance, the more room you have. And the motor
movement is consistent. Looking at some of the speed of you photos
are at 1/1600 seconds, I don't think motor will be an issue. And
none of these should cause a change of focus any way, unless the
lens or camera are not calibrated correctly.

Eric.

Click to expand...

btw.. pls do let me know after you test your 1D2 with 135L at F2 :>

thx1138 said:

Eden did you see my first post? Your DOF is razor thin at f/2 from
10' or less and even at 20" it's not large but large enough to get
a face focus.

Click to expand...

Eden,

Great to know.

Eric.

I am having similar problems. Maybe you find something of interest in this thread :

http://forums.dpreview.com/forums/read.asp?forum=1032&message=18435828

Dan
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