Lenses listed in Group A, Group B, Group C... Why?

[neuroanatomist]

I am not so sure if other/older Canon EOS bodies are not affected in very similar ways ... for all or most of the lenses in categories lower than A.

To a lesser extent, yes.  But the 5DIII/1D X have a more complex system.  Older non-1-series bodies had only a center f/2.8 point, everything else was f/5.6.  Older 1-series bodies had f/2.8-f/5.6 hybrid crosses away from the center, and in the center it was an f/4-f/8 hybrid cross, but on those bodies certain f/4 lenses/combos also activated the f/2.8 crosses.  So it was simpler - either an f/2.8 cutoff for non-1-series, f/2.8 plus a list of f/4 lenses for 1-series.

[BobSanderson]

neuro,
Thanks for the link but I get the following when I click on it:

Referral Denied
You don't have permission to access "http://downloads.canon.com/CDLC/EOS_1DX_AF_Guide_CDLC_Updated_June_2012.pdf" on this server.

Reference #24.b4210e6b.1345828490.388f1e0

[awinphoto]

naw guys, you all have it wrong.... it's a giant coverup conspiracy by canon to push people to buy certain lenses... It's a conspiracy I tell ya!

[Marsu42]

There is a logic to how lenses wind up in different categories.

The thing I'm sorry about is that lenses cannot change their category dynamically - The 100L could have a higher category at non-macro distances, and the 70-300L could have the outer focus points as cross when at f4. Esp. the 1dx/5d3 af and the 70-300L/4-5.6 could give the 70-200/4 sales a push for this reason.

[gtog]

Bob,

I think the "Referral Denied" means you can not access the pdf directly from a link on the Canon Rumors forum since it is not an official Canon site (it is checking what site you are accessing the link from -- the referring site).

If you go to Canon USA's Digital Learning Center and search for the "Master the EOS-1D X's AF System" document, it will provide a download link to the pdf which should work for you.

G

[Marsu42]

I think the "Referral Denied" means you can not access the pdf directly from a link on the Canon Rumors forum since it is not an official Canon site (it is checking what site you are accessing the link from -- the referring site).

... or use something like the "RefControl" Firefox plugin which has a config option to always tell sites that it originates from the same site, circumvents a lot of cross-domain referer checks. It has a whitelist, too so you can except sites that need the real referer.

With this setup, the download of said pdf works just fine :-)