The effect of lens choice on the 5D3's AF

[yakim_peled1]

<p>See the <a href="http://www.canonrumors.com/files/eos5dmkiii-im-c-en.pdf">user manual</a> p.79 to p.84.</p>

<p>Happy shooting,<br /> Yakim.</p>

[Marcus Ian]

<p>Wow. That's an argument for primes and fast zooms if I've ever seen one.</p>

<p>I'm kind of curious how the camera's AF system treats 3rd party lenses. I mean, all the Canon lenses can get put into a database onboard, and referred to when you mount any given Canon EF lens, but I wonder if it 'defaults' to Group H ( for yay! 1 pt AF!) or performs some sort of evaluation to 'sort' the lens once mounted (say by reading the max ape, or 'current' ape?). </p>

<p>At least it will tell you which AF points are operational, and in what mode, so you'll know (even thought there's nothing to be done about it!).</p>

[keith reeder]

<blockquote>

<p>I'm kind of curious how the camera's AF system treats 3rd party lenses.</p>

</blockquote>

<p>If it behaves like the 7D, it'll probably guess - badly - at a Canon equivalent.</p>

<p>My 7D identifies my Sigma 120-300mm f/2.8 OS as a Canon 400mm f/5.6 prime with a 1.4x TC in place; a Canon 135mm f/2 without, and <em>either</em> a Canon 180mm f/3.5 Macro, a Sigma 180mm f/3.5 <em>or</em> a Canon 150mm f/2.8 Macro, with a 2x!</p>

[yakim_peled1]

<p>Looking closer it is evident that the max aperture of the lens has little effect on the rating of the lens WRT these grouping. Even the motor is not a clear indication. Here are f/2.8 examples:<br>

<br /> The 135/2.8 (AFD) is in group A.<br /> The 20/2.8 (ring USM) is in group B.<br /> The 100/2.8 L (ring USM) is in group C.<br /> The 28/2.8 (AFD) is in group D.<br /> The 100/2.8 (ring USM) is in group E.</p>

<p>Happy shooting,<br>

Yakim.</p>

[nail33]

<p>Very interesting. I'm surprised that one of their finest (sharpest and with hybrid IS) lens, the 100mm 2.8L Macro IS, would be in group C, while their cheapest (but very good) 50mm 1.8 is in group A. I wonder what constitutes this decision? Anyone chime in? Sorry Yakim.........I'm not trying to hijack your thread, just curious.</p>

[sravan]

From what I see I think the group is based on the angle of the light rays and the aperture size.

The 100 and 50 mm macros fall into group c. Going to be a differentiator for the 85 1.2L which is in group A

Also wide angle lens seem to need wider apertures to enable more points.

 

I would love if there is an indication of the effective cross points based on the lens in the viewfinder so that I can only use

the cross points that work.

[robin_sibson1]

<p>Marcus, Keith, I don't think that Canon bodies make any attempt at all to identify off-brand lenses. My understanding of the position is that third-party manufacturers of EF-mount lenses have assigned reference codes to them that clash with the codes used by Canon. There is no reason to expect that the data about a particular Canon lens held by the camera body has any relevance to an off-brand lens aliased to that Canon lens.</p>

<p>Yakim, I agree that at first sight this looks a bit of a mess. But when you actually look at the detail, it quickly becomes clear that a large number of the lenses in the later, more restricted, groups are either very old, or are film-era budget lenses that are unlikely to find their way onto a 5DIII. Knock those out and Group D vanishes, Group F reduces to the 800/5.6L IS and the (superseded) 35~350/3.5~5.6L, Group G stays unchanged at the 180/3.5L without or with the Extender 1.4× and the (legendary but discontinued) 1200/5.6L, and Group H vanishes. Evrything down to and including Group E can use all 61 points. Given the coverage of the AF points and the complex relationship between point position and capability, I don't find it at all surprising that apart from these special cases four groups are needed to classify the rest, including with the use of Extenders. But I do agree that there are some slightly unexpected assignments to those four Groups.</p>

[yakim_peled1]

<blockquote>

<p>From what I see I think the group is based on the angle of the light rays and the aperture size.</p>

</blockquote>

<p>So why are the 100/2.8 and 100/2.8 IS in different groups?</p>

 

<blockquote>

<p>Yakim, I agree that at first sight this looks a bit of a mess. But when you actually look at the detail, it quickly becomes clear that a large number of the lenses in the later, more restricted, groups are either very old, or are film-era budget lenses that are unlikely to find their way onto a 5DIII.</p>

</blockquote>

<p>Large number? Yes, but there are some "very old, or are film-era budget lenses" that are high up e.g. 50/1.8 Mk I, 35/2 and 135/2.8 in group A, 24/2.8 and 15/2.8 in group B and 50/2.5 in group C.</p>

<p>Happy shooting,<br>

Yakim. </p>

<p> </p>

[alan_bryant1]

<p>Macro lenses generally get slower as they focus closer; I recall measuring about a 2 stop drop in speed from infinity focus down to 1:1 on two different macro lenses (Tamron 90mm f/2.8 and Sigma 150mm f/2.8). That could explain why they tend to be located lower on the list than other lenses.</p>