Explaining Canon's "Pro Level AF"

[neuroanatomist]

Yes, 40D on up have the dual cross center point. An extender changes the effective aperture, so an f/2.8 lens + 1.4x TC is f/4, so the f/2.8 cross isn't activated.

 

[bigblue1ca]

...Canon proudly advertises that the new 1D X has five f/2.8-sensitive dual cross points, but they don't proudly advertise the fact that the 24-70mm f/2.8L, despite being an f/2.8 lens, only activates one of those five dual cross-type points.

Any idea if the 70-200 2.8 IS II will activate all five points on the 1D X? Or will all five only work with the 300 or 400 2.8 IS II attached?

 

[D.Sim]

Yes, 40D on up have the dual cross center point. An extender changes the effective aperture, so an f/2.8 lens + 1.4x TC is f/4, so the f/2.8 cross isn't activated.

And if a f/4 lens is used with an extender, it wont even focus at all?

 

[Fleetie]

Yes, 40D on up have the dual cross center point. An extender changes the effective aperture, so an f/2.8 lens + 1.4x TC is f/4, so the f/2.8 cross isn't activated.

And if a f/4 lens is used with an extender, it wont even focus at all?

For most cameras, you could use the 1.4x extender for an effective aperture of f/5.6; but you wouldn't be able to AF using the 2x extender, because then you'd be at f/8.

 

[D.Sim]

Yes, 40D on up have the dual cross center point. An extender changes the effective aperture, so an f/2.8 lens + 1.4x TC is f/4, so the f/2.8 cross isn't activated.

And if a f/4 lens is used with an extender, it wont even focus at all?

For most cameras, you could use the 1.4x extender for an effective aperture of f/5.6; but you wouldn't be able to AF using the 2x extender, because then you'd be at f/8.

Yes, I know, but what exactly will happen? Gotta go full manual on the focus?

 

[neuroanatomist]

Yes, I know, but what exactly will happen? Gotta go full manual on the focus?

If you attach an f/8 combo (f/4 lens + 2x extender, f/5.6 lens + 1.4x extender) you'll need to manually focus if you're using the viewfinder. Live View (contrast detect) AF will work.

Any idea if the 70-200 2.8 IS II will activate all five points on the 1D X? Or will all five only work with the 300 or 400 2.8 IS II attached?

Yes, it will activate all 5 AF points. All the details on which lenses activate which AF points can be found on this Google-translated page.

 

[bigblue1ca]

Thanks for the information Neuro and thanks for the link, that's very interesting.

 

[wickidwombat]

if you can find the older kenko DG Teleconverters apparently they will AF because there is no AF confirm like the new DGX ones apparently they are optically the same so these older ones will allow you to AF at greater than f8 even on non 1 series bodies you just have to factor it into your exposure metering thats all.