# Canon 1DX: The AF problem may be bigger that we think?



## John Thomas (Nov 5, 2011)

Hi all,

Seeking the lens market AND the related info WRT Canon 1D X, I found some things which seems concerning:

1st, a note from Canon's Chuck Westerfall (it was quoted also here in some threads) saying:



> â€œAF is unavailable on the EOS-1D X if the maximum aperture reported to the camera through the electronic lens mount is smaller than f/5.6. This is a lower specification than previous EOS-1 series DSLRs. [...]"



Having in mind the above, this means that _*Canon 1D X cannot focus on the longer (telephoto) lenses which have an aperture smaller than f/5.6, say 6.3?*_

This includes (at least) the following lenses:

From Sigma:

50-500mm F4-6.3 EX DG HSM
150-500mm F5-6.3 APO DG OS HSM
50-500mm F4.5-6.3 APO DG OS HSM
28-300mm F3.5-6.3 DG Macro

From Tamron:

28-300mm VC F/3.5-6.3 XR Di VC LD Aspherical [IF] MACRO
28-300mm VC F/3.5-6.3 XR Di LD Aspherical [IF] MACRO
SP 200-500mm F/5-6.3 Di LD [IF]

_...so, by buying Canon 1D X and having at least one of the above lenses and raking out the glass, one cannot use the AF anymore?_


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## bikersbeard (Nov 5, 2011)

I bet Nikon are pissing themselves laughing :-[

and probably even more when the D4 is announced..


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## neuroanatomist (Nov 5, 2011)

1. This isn't news, there is a separate CR main page post and long thread on the f/8 issue with the 1D X. 

--more importantly--

2. The issue you describe isn't an issue at all. No worries about the Sigma or Tamron lenses. They spoof the camera into thinking they're f/5.6 at the long end. Keep in mind, only the previous 1-series bodies could AF at a max aperture narrower than f/5.6. Those lenses you list all AF on any Canon body, 7D, 50D, whatever, right? Then they'll AF on a 1D X, too. 

The 'problem' is f/5.6 lenses with a 1.4x TC or f/4 lenses with a 2x TC will not AF on the 1D X, but would on past 1-series bodies.


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## Flake (Nov 5, 2011)

"Having in mind the above, this means that Canon 1D X cannot focus on the longer (telephoto) lenses which have an aperture smaller than f/5.6, say 6.3?

This includes (at least) the following lenses:

From Sigma:

50-500mm F4-6.3 EX DG HSM
150-500mm F5-6.3 APO DG OS HSM
50-500mm F4.5-6.3 APO DG OS HSM
28-300mm F3.5-6.3 DG Macro

From Tamron:

28-300mm VC F/3.5-6.3 XR Di VC LD Aspherical [IF] MACRO
28-300mm VC F/3.5-6.3 XR Di LD Aspherical [IF] MACRO
SP 200-500mm F/5-6.3 Di LD [IF]"

Erm no it doesn't because the Sigma lenses at f/6.3 report to the camera that they are f/5.6 or they wouldn't work with any other camera than the 1D series. I suspect that the Tamrons use the same system.


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## Fleetie (Nov 5, 2011)

Ok, I have a few more questions then - purely because of my ignorance about how these lenses "lie" to the camera body about their aperture:

1) Does the fact that the lens lies to the body about its max aperture affect exposure in non-manual shooting modes? The lens actually lets in less light than it says it can, so.... It may not matter, if the exposure is judged and integrated while the shutter is open, until the camera "thinks" enough light has accumulated on the sensor.

2) (Do Canon DSLRs do that? Or do they determine how long to expose when the shutter is fired, and always keep the shutter open for that pre-determined time period? My Olympus film SLRs meter WHILE THE SHUTTER IS OPEN by measuring with an "OTF" ("Off-The-Film") light sensor, that measures reflected light from the film surface.)

3) Does this incorrect f/5.6 aperture show up in EXIF data as f/5.6, if you shoot with the lenses wide-open?


Just curious.


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## dr croubie (Nov 7, 2011)

dilbert said:


> Maybe Sigma/Tamrom will need to pull their finger out and produce newer, better lenses that don't drop down to f/6.3 at the long end?



Maybe they will, but then they'll have to charge closer to Canon's prices, and Sigron are more concerned about the cheaper end of town.

As for how the camera meters with the f/6.3 lenses, I'm not sure, but here's an idea:
The lens tells the camera it has f/5.6, when it really has f/6.3. But the aperture is wide open at that point. If you set the aperture at f/5.6 on the camera, everything will meter properly.
But if you set the aperture at f/6.3 or larger, then the camera will change the shutter speed by 1/3 but the aperture blades won't move because it's still f/6.3.
Maybe the lens just always under-reports by 1/3 stop, so choosing f/6.3 will close the blades to f/7.1? Then the metering will always be correct, but the EXIF will be out by 1/3 of a stop.

Anyway, (afaik) noone uses OTF metering anymore for normal exposures (although in a way there is when using an ETTL flash). In a canon the exposure is decided when you press the button, then the aperture blades close and the shutter fires for the right amount of time...


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## Fleetie (Nov 7, 2011)

dr croubie said:


> Anyway, (afaik) noone uses OTF metering anymore for normal exposures (although in a way there is when using an ETTL flash). In a canon the exposure is decided when you press the button, then the aperture blades close and the shutter fires for the right amount of time...



Thanks for that info.


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## Tov (Nov 7, 2011)

dilbert said:


> Flake said:
> 
> 
> > "Having in mind the above, this means that Canon 1D X cannot focus on the longer (telephoto) lenses which have an aperture smaller than f/5.6, say 6.3?
> ...



I doubt that a person who can afford a 1Dx will bother much with these lenses.


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## AprilForever (Nov 7, 2011)

If I had a 1DX, and spent the pile of cash on it, I would not be buying ANY of those lenses. I would instead be nabbing up a 400 2.8, a 600 f4, a 200 f2, and maybe a 100-400 for fun! And when the fabled 200-400 would come out, I would buy two of them, just to be on the safe side!


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## xROELOFx (Nov 7, 2011)

AprilForever said:


> If I had a 1DX, and spent the pile of cash on it, I would not be buying ANY of those lenses. I would instead be nabbing up a 400 2.8, a 600 f4, a 200 f2, and maybe a 100-400 for fun! And when the fabled 200-400 would come out, I would buy two of them, just to be on the safe side!


haha, you forget hiring someone to carry all that heavy stuff for you


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