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Archive 2013 · Question about 1D Mark IIN AI Servo AF
  
 
AmatureMic
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p.1 #1 · Question about 1D Mark IIN AI Servo AF


I've acquired my third (and final) Mark IIN body and have a question:

1) when setting the body to AI-SERVO (using central AF point only/no expansion/standard AI Servo tracking sensitivity) using a standard 50mm 1.4 USM lens, the camera tends to continuously "refocus/move slight fine focus" even when locked solid on a tripod and the subject is not moving (like a resolution chart). This I find strange (I shoot Nikon also and none of my Nikon's do this) because the camera tends to feel overly erratic/hyper and doesn't stop focusing. Could this be the normal way the Canon's focus in AI Servo? It tends to feel overly active and aggressive at wanting to refocus immediately.

Any help is appreciated.


PS: these 1D-series bodies are dust magnets! The viewfinder area (condenser lens sandwiched btwn the pentaprism and focusing screen) tends to get dust permanently trapped inside regardless how careful you are at changing lenses/protecting the body when body cap is off). It keeps building up.



Feb 27, 2013 at 04:01 AM
mttran
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p.1 #2 · Question about 1D Mark IIN AI Servo AF


Your subject is not moving but your 50f1.4 optical projection plane does while its element(s) was/were moved by 1D2N's AF. This sequence repeats until the AF sensor(s) no longer see any error.

Regarding the dust...avoid the blower and use any low speed vacumn with small tube ( starbuck coffee straw) to suck them all out. You need to lock your shutter and mirror (sensor clean mode) before doing anything. This vacumn process is not recommended if you really don't know what you are doing. I hardly clean my 1ds2 sensor...maybe once/twice a year.




Feb 27, 2013 at 04:18 AM
AmatureMic
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p.1 #3 · Question about 1D Mark IIN AI Servo AF


mttran,

Thanks a bunch.

This is quite strange because the target in front (focus resolution chart) was prefocused and had achieved focus already but the lens continues to "chatter" the focus slighting and continoulsy. My cheaper Rebel/30D/EOS T2 film bodies don't have this "continual chatter" when in AI Servo and have focus achieved. Like I mentioned: could this be a characteristic of the 1D bodies or just a faulty body, I don't know.

Firing a burst of 20 RAW images (locked on the tripod with neither camera or target moving), the camera managed almost all focused w a few slight OOF images.

I've also noticed with this 1D body, when the two subjects (of different distances) are nearby to each other, the AF tends to "shuffle" forward and back sometimes (can't decide to focus on further or closer subject). This may be due to the AF point indicator being a bit smaller than what the AF sensor is really detecting, but this again is totally different from Nikon's AF approach.



Feb 27, 2013 at 04:59 AM
mttran
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p.1 #4 · Question about 1D Mark IIN AI Servo AF


The differences between 1dseries and lesser AF bodies is the AF motion prediction firmware. Your 50f1.4 is low contrast lens when it's in wide open. Just look at the 50f1.4 projection curve from SLRGEAR you can tell the movement of 50f1.4 focal plane does fool the 1D2N's AF motion prediction firmware. Try another lens like 135L then you won't see the same action from 1D2N in AF SERVO mode.

http://slrgear.com/reviews/zproducts/canon50f14/ff/tloader.htm
http://slrgear.com/reviews/zproducts/canon135f2/ff/tloader.htm

just playing with aperture tag, you can see the 50f1.4 focal plane changing but not much in 135L



Feb 27, 2013 at 05:16 AM
 

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AmatureMic
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p.1 #5 · Question about 1D Mark IIN AI Servo AF


mttran,

Thanks again!

Ok, so from what you're saying is due to the lens being "low-contrast" (since the lenses are always wide open before the shot is taken to allow light hit the AF sensor), it confuses the 1D body to do this chattering (due to its high-speed prediction algorithm vs. the lower-end AF modules) and become overly re-active in AI-servo mode.

I'll have to dig up a 70-200 2.8 and a slower speed lens to test the above soon. But it sounds very interesting (especially coming from Nikon's AF).

I did notice when I had borrowed the 70-200mm II IS (stablizer off) attached to this 1D IIN body, that the AF is far quicker to initially lock focus vs. my D700 with the 80-200mm AF-S. The fine focus mechanics on the 70-200mm II IS is far shorter than the 80-200mm AF-S (as much as 1.5" more of turn mechanically from infinity to MFD). But the tracking method is far more stable on the D700 vs. the 1D IIN: hence the erratic/quick refocus of the Canon's AI Servo AF. I love the focusing speed, but not this overly erratic focus method too much (this was evident with all 3 bodies I had).

Also, when focusing from a near to close subject (such as focusing a quarterback then onto a receiver), the Canon is quicker at acquiring focus. Tracking is same with both system (with the Canon being more erratic).



Feb 27, 2013 at 05:36 AM
mttran
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p.1 #6 · Question about 1D Mark IIN AI Servo AF


AmatureMic, i am not a sport shooter and hoping someone will chimp in and help you soon. At the mean time, we have one canon document that might help you to fine tune your 1D2N custom AF tracking to prevent the erratic that you have mentioned: http://media.the-digital-picture.com/Information/Getting-The-Most-From-Your-EOS-1-Series-Camera.pdf

Page 14, Custom Function 20 controls the degree of focusing “sensitivity” in AI Servo AF



Feb 27, 2013 at 06:28 AM
mark fadely
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p.1 #7 · Question about 1D Mark IIN AI Servo AF


The chattering is normal and the 1DIIn. The chattering will vary from lens to lens but it never bothered me. I also had dust in the viewfinder of all my MKIIn's, but that never really bothered me either The camera has a great AF and is always searching in servo mode. Of course there is no chatter in one-shot mode. That camera makes some wonderful images no matter what you are shooting.


Feb 27, 2013 at 08:04 PM





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