Focus point types

JohnN

JohnN

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Afternoon,

I had a little chat with Canon regarding focusing and he asked what lens I primarily used for my fast motion work - I told him the Sigma 50-500 OS, now he didn't trash it at all but did point out that the aperture wouldn't be wide enough at anything other than to 50mm end as the sensor could not work as a cross type.

If this is so (and I'm sure it is), that would explain the existence of massively expensive primes!

Can someone explain the cutoffs and how this work?
 
Ah, I found this:

Here's the AF info from the white paper...All MkIII cross-type sensors are active at f/2.8 or faster on vertical, and f/5.6 or faster on horizontal, with the exception of the center point, which is active at f/4 or faster on the vertical, and f/8 or faster on the horizontal. The 20D center cross-type is active at f/2.8 or faster on the vertical, and f/5.6 or faster on the horizontal.
Click to expand...

eos-1d-sensor-layout-comparison.GIF

So if I read that correctly anything F4 and under utilises the cross type on the centre point - once it goes over (up to F8) it becomes horizontal and the other cross types remain cross types at 2.8 but switch to horizontal up to 5.6.

Sooo.. My Tamron 70-300mm f4-5.6 will be cross type in the centre and horizontal elsewhere, but the Sigma 50-500mm f4.5-6.3 OS will always be horizontal.

Interesting stuff that I never knew.
 
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AIUI up to and including current 1 Series bodies will AF with any lens F8 or faster (centre point only), all other bodies (5D, 7D, XXD etc) need F5.6 or faster (including the new 1DX, which is why lots of people moaned).
Want aware it was differniated hoz/vertical though.
 
Does anyone know *why* it is like this?

Note the behaviour varies from camera to camera. Check your manual.
 
Costs, marketing and how Canon's work it so some models AF better than others.
 
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