Canon Japan EOS-1D X The Birth of Entirely new Flagship

[J. McCabe]

But if the sub-exit pupils are located outside the boundaries of the exit pupil of the lens proper (as when the lens aperture during AF is smaller than that which supports the sub-exit pupil spacing of the particular detector pair of interest), then the AF detectors get no light at all, and thus cannot function.

And, prudently, the camera body declines to include various classes of AF detectors from the AF scenario based on knowledge, reported by the lens, of its maximum aperture.

Thanks, Doug! 

A follow-up question occurs to me.  How is it that when a subset of the electrical contacts on the teleconverter are covered with tape, so the aperture is not reported to the camera, the phase detect AF system wil attempt to achieve a lock, and in some cases it can do so (given sufficient contrast)?  Similarly, how do some 3rd party lenses, such as the Tamron and Sigma zoom lenses that have a maximum aperture of f/6.3 at the long end, manage to retain normal AF?

AFAIK, the Tamron and Sigma lenses send false information (read: that the aperture is at f/5.6 when it's actually f/6.3)

[neuroanatomist]

AFAIK, the Tamron and Sigma lenses send false information (read: that the aperture is at f/5.6 when it's actually f/6.3)

Yes, I know...but Doug stated, in effect, that at lens apertures narrower than specificed for the AF system, i.e. f/5.6, the AF detetors cannot function at all, i.e. it's an optical limitation, as opposed to a firmware limitation.  The fact that an f/6.3 lens can AF, as can an f/8 lens under certain conditions, with an f/5.6-sensitive sensor, suggests that it's a firmware limitation, and not an optical limitation. 

[xps]

Great Idea! Is there an possibility to do this with original canon lenses too?

I just returned from an wildlife-photographer meeting (birdwatching) and the whole group was disappointed by this new camera.
Does anybody know (or has an rumor), what Canon wants to do with these persons that need the "working AF at least @ f=8 performance" , you just posted before? (soory for poor English, Its not my native language).

[neuroanatomist]

It's possible now with original Canon lenses, but it's not supported or condoned by Canon.  You just put a small piece of Scotch® tape over the first three pins (i.e. on the counterclockwise side) on the rear side of the teleconverter (the side that mounts to the camera).

[CarebbianTraveler]

Yes, I know...but Doug stated, in effect, that at lens apertures narrower than specificed for the AF system, i.e. f/5.6, the AF detetors cannot function at all, i.e. it's an optical limitation, as opposed to a firmware limitation.  The fact that an f/6.3 lens can AF, as can an f/8 lens under certain conditions, with an f/5.6-sensitive sensor, suggests that it's a firmware limitation, and not an optical limitation.

Well, the pupils have a certain size, and at f/5.6, they're not shaded at all and the focus sensors get the full amount of light. But when you attach a slightly slower lens as f/6.3 they start to get shaded, but there's still light coming thru to the sensors. So it works worse in low-light conditions. As people report here, the pupils are nearly fully covered at f/8 depending on the lens. This is why it may still work with a lot of light.

[Bokehmon]

NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO! They've made the monochrome LCD backlight orange! Y U NO PUT BLUE BACKLIGHT LIKE BEFORE CANON!?!?!

[dougkerr]

Hi, CT,

Yes, I know...but Doug stated, in effect, that at lens apertures narrower than specificed for the AF system, i.e. f/5.6, the AF detetors cannot function at all, i.e. it's an optical limitation, as opposed to a firmware limitation.  The fact that an f/6.3 lens can AF, as can an f/8 lens under certain conditions, with an f/5.6-sensitive sensor, suggests that it's a firmware limitation, and not an optical limitation.

Well, the pupils have a certain size, and at f/5.6, they're not shaded at all and the focus sensors get the full amount of light. But when you attach a slightly slower lens as f/6.3 they start to get shaded, but there's still light coming thru to the sensors. So it works worse in low-light conditions. As people report here, the pupils are nearly fully covered at f/8 depending on the lens. This is why it may still work with a lot of light.

And the body may in fact let the AF system (try to) work at a reported aperture of f/6.3. But not f/8

Best regards,

Doug

[dougkerr]

Hi, N,

AFAIK, the Tamron and Sigma lenses send false information (read: that the aperture is at f/5.6 when it's actually f/6.3)

Yes, I know...but Doug stated, in effect, that at lens apertures narrower than specificed for the AF system, i.e. f/5.6, the AF detetors cannot function at all, i.e. it's an optical limitation, as opposed to a firmware limitation.  The fact that an f/6.3 lens can AF, as can an f/8 lens under certain conditions, with an f/5.6-sensitive sensor, suggests that it's a firmware limitation, and not an optical limitation.

The fact that the camera will not allow the AF system to attempt to work below a certain aperture is a firmware limitation.

The fact that it will not work (or work well)  below a certain aperture is a hardware (optical) limitation.

As others have pointed out, the latter is not "knife-edge". If we can force the camera to "let the AF work" at an aperture of, for example  f/8 (for an "f/5.6" AF detector). it may work with some difficulty. At f/6.3 it will likely work "pretty well".

Best regards,

Doug

[neuroanatomist]

That's what I thought, Doug, but expert confirmation is always appreciated!

Best,

John