1D MKIII Predictive Focus AI-SERVO

1D MKIII Predictive Focus AI-SERVO, Single Centre point AF

I was wondering if anyone knows how C.Fn III-2 AF system sensitivity affects the way the MKIII focuses @ 10FPS on a subject i.e. fast motorcycle accelerating from 30mph to 100mph towards the camera. Is the AF system capable of predicting an accelerating object moving at a non constant speed, if the camera is not capable of predicting the speed I would think the MKIII would not be able to focus accurately on all of the burst of shots. Which C.Fn III-2 setting would be best -2 -1 0 +1 +2 . Hope I have explained my question properly?

Cheers

Nick,

My understanding of CF III-2 is it only affects how slow or fast the camera shifts the focus from the initial target to another target that fills the focus area. As long as you keep the ceter focus point on the bike, CFIII-2 will not make any difference.

For motorcycles, I would guess that the ring of fire would be the prefered focus method with CFIII-2 set at 0 or a negative number to make the camera slow to shift focus off the bike.

it affects how fast it analysis the focal point and adjust focus.

From a Canon PDF file on the CF http://www.robgalbrait​h.com …-1D_Mark_III_C.Fn_III.p​df:

C.Fn III-2: AF system sensitivity to sudden subject changes when in AI Servo mode
0 — Standard sensitivity (AF tracking will momentarily pause if the AF point sees another subject while tracking)
-2 — Slow (Tracking will pause for a longer period when AF is disrupted to allow the photographer to find original subject)
-1 — Moderately slow (Pause length will be in between setting -2 and 0 )
+1— Moderately Fast (The AF system will respond faster to a change in subject position)
+2 — Fast (AF system will not pause, if a change occurs camera will instantly re-focus)

This custom function adresses the different focus tracking needs of various photographers. It adjusts how the AF system will respond if when tracking a moving subject (AI Servo mode), you lose your subject and find your AF point now in the distance, or if something closer moves in front of you subject. Important: It does NOT change the speed at which the camera can track a continuously-moving subject. It only deals with how quickly the system will try to focus upon something different, if the active AF point no longer sees your moving subject.


Steve,
Your photos at VIR are awesome!

Steve Beck wrote in post #3917592
it affects how fast it analysis the focal point and adjust focus.

Steve, I know you shoot bikes have you experimented with C.Fn III-2? I have never changed from mid standard setting. How I look at this setting with an erratic accelerating bike coming towards you there is know way that if AF points drifts of the bike the camera can predict where the bike is the next time the point is over the bike because the bike is not moving at a constant speed. If this is the case setting the C.Fn III-2 to +2 will speed up the AF to help the camera reacquire the focus on the bike. Obviously in theory you would loose focus quicker which could be a problem if focus point is not nailed.

Cheers

Merciez wrote in post #3917247
Nick,

My understanding of CF III-2 is it only affects how slow or fast the camera shifts the focus from the initial target to another target that fills the focus area. As long as you keep the ceter focus point on the bike, CFIII-2 will not make any difference.

For motorcycles, I would guess that the ring of fire would be the prefered focus method with CFIII-2 set at 0 or a negative number to make the camera slow to shift focus off the bike.

Steve, Thanks, in theory you are correct but in real world shooting situations I am not sure, I have a bike meeet at the weekend so I will test C.Fn III-2 settings. I've tried ROF (ring of fire) never had any success with that, I like to nail the focus myself instead of letting the camera decide where to focus for me.

Cheers

Thanks Merciez, I feel great about them. Appreciate you looking at them and commenting.

as far as i know +2 has nothing to do with how fast the AF works but how fast it regains focus should you take the focus point of the subject .
i think +2 is the way to go you not only can lose focus quicker if you wonder of target but you regaing it quicker so your job is to try not to lose it at all .
i look at it this way +2 is instant -2 it sort of thinks about it.
Rob.

I have been getting such good results shooting bikes and racing in general i did not want to dork around with the custom functions to much.

Steve Beck wrote in post #3921497
I have been getting such good results shooting bikes and racing in general i did not want to dork around with the custom functions to much.

Steve, Same here, but this pumping the AF business to get the camera to refocus is a little irritating anyway I'll do some test this weekend, I've got 3 days to test at the track.

Cheers