Is the Canon 5D Mark II autofocus accurate enough for f/1.2 lenses, and is the 5D Mark III better?
Asked 3/17/2013
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I use a Canon EOS 5D Mark II with very fast lenses such as f/1.2 and f/1.4 primes, and I’m struggling to get consistent autofocus. Is the 5D Mark II AF system accurate enough for lenses this fast, or could my camera be faulty? Would upgrading to a 5D Mark III noticeably improve autofocus accuracy and consistency?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
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According to this Blog post by LensRentals.com owner Roger Cicala, the 5DIII has less than 1/2 the standard deviation of the 5DII with regards to Phase detection Auto Focus. But to get that additional benefit, one must also use Canon lenses introduced since about 2010. All of the testing was done using the center focus point.
In general, using the center focus point should yield faster, more accurate focus with faster lenses such as the 50mm f/1.2L and f/1.4. The 5DII can be an exception to this rule. When shooting in AI Servo AF, if C.Fn III-07 is enabled, there are six small AF Assist Points clustered within the spot metering circle that are active in addition to the Center Focus Point. The location of these six AF Assist Points are not indicated in the viewfinder! Yet the camera may be using one of them pointed at something that has higher contrast than what is located behind the square in the middle of the viewfinder when it decides the focus distance.
Here's the Map for the 5DII's focus system.
The entire series will tell you just about everything you've ever wanted to know about phase detection AF accuracy and consistency.
Autofocus Reality Part 1: Center-Point, Single-Shot Accuracy
Autofocus Reality Part II: One vs. Two, Old vs. New
Autofocus Reality Part 3a: Canon Lenses
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
13y ago
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Generated from our catalog & community — verify before relying on it.
Very fast lenses make autofocus look less consistent because depth of field is extremely thin. At f/1.2, even around 10 feet, you may have only a few inches of acceptable focus, so small AF errors or subject movement become obvious.
The 5D Mark III does offer clearly better phase-detect autofocus performance than the 5D Mark II, especially with the center point, so upgrading should improve consistency. However, that does not mean every f/1.2 lens will suddenly feel easy to use.
The EF 85mm f/1.2L II in particular is known to autofocus more slowly than average, and that behavior remains even on the 5D Mark III. So yes, the body upgrade helps, but the lens itself can still be challenging.
For best results on the 5D Mark II, use the center AF point for the highest accuracy. Also be aware that on the 5D Mark II, certain AI Servo settings can activate hidden assist points around the center point, which may affect where focus lands.
So: the 5D Mark II can work with f/1.2 lenses, but consistency is demanding; the 5D Mark III is meaningfully better; and some difficulty is normal rather than proof your camera is faulty.
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AI13y ago
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