The biggest one I have seen is the omission of f/8 AF sensors. ... I am still waiting for official confirmation from Canon about this issue. Is it a hardware thing? or could it be addressed with software?
Chuck Westfall provided confirmation of the lack of AF at f/8 in a reply to Art Morris referenced on another forum. Granted, that's not official. Here's the link
, and here's the quote from Art Morris: "...I would have to classify this info from Canon USA's top tech rep Chuck Westfall as bad news (just received via e-mail):
"AF 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. On the plus side, consider the fact that with most f/4 lenses including the 400 DO, 500/4L IS and IS II, and 600/4L IS and IS II, you now have 41 cross-type AF points plus color and face detection, whereas you had no cross-type points and no color or face detection during AF with previous EOS-1 series DSLRs using the same lenses, not to mention a significantly wider AF coverage area from left to right."
It's a hardware thing. The 1D X is the first 1-series body to have a diagonal f/2.8 cross point. That's the f/5.6 +-shaped sensor with an f/2.8 x-shaped sensor superimposed on it. That's a pretty crowded arrangement already, and it may there was just no room for the additional f/8-sensitive line. Maybe the engineers at Canon can redesign it...but that's a pretty tight timeline for design, testing, and production to meet a March release.
I hope that Canon addresses it before release, but I have doubts - I don't think it was an oversight. As stated, there seems to be a technical reason...but my cynical side wonders about marketing's role - take away the 1.3x, but some users can compensate by adding a TC; take away f/8 AF and that forces more people to buy longer lenses.
As a side note, the AF system on the 1D X does have other quirks. For example, those f/2.8-sensitive sensors? There are five of them, but only with certain lenses. Some f/2.8 lenses only activate the center f/2.8 point, and the other 4 f/2.8 points act as f/5.6 only - that's mostly the f/2.8 wide angle primes (28mm and wider), but also includes the 24-70mm f/2.8. In fact, two f/2.8 lenses - the 100mm L and non-L Macro lenses - do not activate any
of the f/2.8-sensitive AF points. Full details on this Google-translated page
This means that a 500 f/4L IS with 2X teleconverter wouldnâ€™t have AF at the center point...
Or, more importantly, the 500mm f/4L IS II
(and 600/4 II) + 2x will not AF. The irony is that Canon announced new MkII 500mm f/4 and 600mm f/4 lenses and touted their impressive performance with MTF curves showing performance with the new 2x III extender that's nearly as good as the bare MkI lenses. Those MTF curves with the 2x are on Canon's lens pages for the 500 II
and 600 II
, and are even placed before the bare lens MTF curve to highlight them. Quite tantalizing.
Then they replace their professional bodies with the 1D X, which cannot AF with that combination. Bait...and switch. Oops.
To guess at why, maybe trying to allow for autofocus with an f-stop of 8 requires sacrifices in AF sensor accuracy?
Exactly. The key there is 'proper' - yes, you can tape pins and make the AF system try to work with a lens slower than it's designed for, and sometimes it works...but many times it fails, which is why Canon limits it to the specified aperture.
The F8 limitation is only on a lens whose maximum aperture is F8 or smaller.
As far as I'm aware Canon doesn't make any, at all.
Even with a x2 Extender which changes the aperture by 2 stops this is only when the picture is being taken.
When the camera focuses it uses the whole width of a lens. So, even if you are in AV mode, set at F11, the lens will still be at F2.8 until you take the picture AFTER it's already focused. ( like with a 24-70 2.8 )
Sorry, but the first part of that is wrong. With a 2x extender, you lose two stops of light - all the time. It's not that adding the extender causes the camera to stop down the aperture of the lens 2 stops. The addition of the extender results in an actual loss of light (because the light from the central portion of the image circle is being spread over a wider area, there's less of it). Basic optical physics. We use aperture to mean f/number, but the f/number is actually the ratio of focal length to iris diaphragm diameter. That's why an f/2.8 lens with a 400mm focal length has to be so much bigger than an f/2.8 lens with a 100mm focal length - the former needs an iris diaphragm 4 times larger, and therefore bigger elements to fill that hole with light. When you add a teleconverter, you 1.4x or 2x the effective focal length, but you don't make the iris diaphragm any bigger. Therefore, you decrease the effective
So, yes, with a 2x TC on an f/4 lens, the lens will be set to f/4 during AF no matter what the chosen aperture for the shot is., stopping down only at the moment of the exposure. But that f/4 setting with the TC is only letting an amount of light reach the sensors that's equivalent to f/8. That's why Canon forces the AF to stop working when a teleconverter results in a maximum effective aperture that's not supported by the camera's AF sensor.