1DmkIII AF optimised for sports, not fast primes?

futureal33

futureal33

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Ok, before I start, if I saw someone else posting this I would probably chime in that they were wrong. However.....

I have just spent the last 4hours reading Canon 1DmkIII reviews, in particular those vs the 1DsMkII and 5D series.

Several times, the fact that the AF on the 1DmkIII is not designed for fast primes (f1.2-2.8) was mentioned, on several different websites and forums. I wouldn't have believed this if Id seen it just once... but the fact it keeps getting mentioned caused me some doubt..

So... in a nutshell.. What are people's opinions on the AF on the 1DmkIII - obviously it is primarily a sports/wildlife camera used on 70-200's and the like... but if used in a wedding scenario, with 35Ls', 135L's etc... would the AF be perfectly fine and accurate at those apetures.

I currently use a 5Dmk3 and love the AF system that camera has, but interesting in getting a 1DmkIII as secondary camera

Thanks :)
 
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Well I have used mine with a 135mm f/2, 85mm f/1.8, and a 50mm f/1.4 and they all work perfectly. I have never heard this before.
 
Are you talking about how 19 out of the 45 AF points on the 1D3 are cross-type AF points for f2.8 and faster ?

You've probably read it but half way down here might explain better than me typing it....

http://www.imaging-resource.com/PRODS/E1DMK3/E1DMK3A4.HTM

The remaining 26 AF sensors have been demoted to "assist" sensor status. They contribute to AF operation, but can't be independently selected under user control. We don't see this as a limitation of any practical extent, as we've almost never found ourselves caring greatly whether we selected one particular AF point on the EOS-1 cameras or the one next to it. (Actually, we'll welcome only having to scroll through 19 sensors when making our manual AF selections, the selection process would go that much more quickly.)
The legend on the diagram above makes reference to "f/2.8 sensors" and "f/5.6 sensors," and also notes that the Center AF point is "f/4." Without going into all the details of how phase-detect autofocus systems work, at the heart of it is the need for light rays to reach the AF sensor, passing through different parts of the lens' optics. When the aperture is large, you can separate the light rays more widely, providing a longer "baseline" for the AF system, and in the process improve its accuracy. When the aperture is small, though, the light rays can't reach widely-separated sensor elements. Any AF elements having a wider separation than that allowed by the current aperture setting simply stop working, because they're not seeing any light from the subject at that point.

What this means for the EOS-1D Mark III is that its more closely spaced horizontal-sensitive AF arrays can work at f/5.6, while the more widely-separated (and therefore more accurate) vertical-sensitive arrays can only work at apertures of f/2.8 and larger.
 
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Well mine gets the shots at f/1.8 (85mm) where wouldn't even expect it to. 50mm had a couple random misses in awful light, but it's mostly reliable. There is almost no difference from 1Ds2. But if you started looking for a few bad frames in a 20 frame burst like some pro shooters did, then you would probably find those. Get 1Dx if that is a dealbraker.
 
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