Gear Talk > EOS Bodies - For Stills

1Dx / 5D3 AF system limitations, a (perhaps stupid) question

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3kramd5:
So, per the DP review description,

"The 5D Mark III loses out to the Nikon D4 and D800 when it comes to use with slower lenses or long lens/teleconverter combinations, in that its cross-type points can only be used with lenses that are F4 or brighter (and the double-crosses with F2.8 and brighter lenses). Canon says there's a trade-off to be made and that its approach allows the sensor to be more accurate with the large aperture lenses it expects its customers to use, and allows the F4 cross-type sensors to be placed further towards the edge of the frame."



So, the middle AF point (and indeed much of the center column) is double cross type. All points in the center three columns are either cross or double-cross points.

Does that mean that, if I'm using an f/5.6 lens (say 100-400 at max focal length), I would only be able to use points from columns 1, 4, 8 and 11? Or will the higher accuracy points function with less fidelity? Can I not use the center point with my 25-105?

Seems kinda foolish to force focus off center for slower lenses.

Mt Spokane Photography:
That display on DPR is pretty confusing, there are three charts in one, and you use the buttons underneath to select them.

Go back to DPR and click on the three buttons under the chart to see which points are active as just horizontal points(white),  cross type points(Orange), or double cross type points(blue with x) with the three types of lenses.  The double cross points work with the wide primes because they need more accuracy to get accurate focus.

http://www.dpreview.com/previews/canoneos5dmarkiii/4

All 61 points work with all canon lenses f/5.6 or brighter, and 21 of them are cross type points..

1. f/2.8 or brighter



2. with lenses f/2.8-f/4



3.  With lenses f/5.6 or brighter.

3kramd5:
A'ha.

Thanks.

That would have been a deal breaker.

neuroanatomist:
Not at all.  Every one of the 61 points is single orientation-sensitive (horizontal lines) at f/5.6.  The middle three columns are f/5.6 crosses (with the central column of dual crosses also having a superimposed diagonal f/2.8 cross, which is what makes them dual crosses).

So, with most f/5.6 lenses, you have 21 cross-type points (middle 3 columns) and 40  lines.  With most f/4 lenses, you have 41 cross-type points (all the orange and blue ones in the diagram) and 20 lines, and with most f/2.8 lenses you have 5 f/2.8 (more accurate) crosses, plus 36 other crosses (all the orange) plus 20 lines. 

So, almost all f/5.6 and faster lenses use all 61 points, what varies is the number of those points that act as crosses vs. lines. 


--- Quote from: Mt Spokane Photography on March 10, 2012, 11:18:34 PM ---All 61 points work with all canon lenses f/5.6 or brighter

--- End quote ---


Not quite.

I'm using 'most' because there are some exceptions. For example, the 24-70mm activates only the center f/2.8 cross, not all five, despite being an f/2.8 lens, the 100mm f/2.8L macro lens doesn't activate any f/2.8 crosses (but still uses all 41 regular crosses + 20 lines).  I say 'almost all use 61 point' because some very old zoom lenses, and the insanely expensive 800/5.6L IS, use only 47 total (the left/right sides drop off), and the 180L Macro only uses the central 33 of the 61 points.

Full details on which lenses activate which AF points can be found on this Google-translated page

That was probably way more than you wanted to know...   :P

3kramd5:
^^

Yes, but it's interesting nonetheless. Thanks for the link.

How does the camera know? By communicating with the lens? Begs the question as to what happens when you strap on off-brand glass...

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