5d iii autofocus points.

[Dave Johnston]

Hey all,

Anyone else have a 5d3 and a 100mm 2.8 non-L that could chime in? In the 5d manual says that this lens and the 70-200 f4 are in the same lens grouping (refering to autofocus usage) and can use the outer cross type points. When I select the function for only cross type points to be available, the 70-200 has all the 21ish in the center as well as the ones on the sides approx ten each closer to the "rule of thirds" region.

When I plug in my 100 2.8 macro, I only get the center 21 with the same function enabled. Is this my lens? er am I missing something?

Dave.

[Dave Johnston]

Nevermind. Was looking at the "older" 100mm macro.

Cant freaking believe the USM one is not using all the cross type points! What in the world, Canon? Is this marketing for the L version or is there some hardware inconsistency that I am not recognizing?

[neuroanatomist]

Macro lenses are generally one group 'lower' than their aperture would suggest. I suspect it's due to the apparent aperture decrease at macro distances. This has been the case for a while, long before the 5DIII/1D X - for example, the 180mm f/3.5 with the 1.4x TC will only AF with the center point of pre-1D X 1-series bodies, despite a reported aperture of f/5.

[Dr Croubie]

Macro lenses are generally one group 'lower' than their aperture would suggest. I suspect it's due to the apparent aperture decrease at macro distances. This has been the case for a while, long before the 5DIII/1D X - for example, the 180mm f/3.5 with the 1.4x TC will only AF with the center point of pre-1D X 1-series bodies, despite a reported aperture of f/5.

But the 'apparent aperture' only gets narrower when you're at higher magnifications. Does that combo AF at infinity (where the aperture would be f/5) and not at macro? Or is there a firmware thing that just stops it from AFing at all times so as to not confuse people ("it AFs at infinity but not at macro, it must be broken!")

[neuroanatomist]

It's a firmware thing, just like with the 24-70 MkI and some f/2.8 wide primes being in Group B.

[Dave Johnston]

Macro lenses are generally one group 'lower' than their aperture would suggest.

Even still, the 100mm 2.8 L macro is in group b, and the older non-usm 100mm 2.8 macro. Why does the USM version get the shaft?