Canon Wannabee's AF Question

[SantaFeBill]

I'm a Nikon user with a bad case of CAS. :lol: But I find that I'm puzzled by as aspect of AF for Canon-mount lenses.

One of Canon's advantages is that the mount doesn't use a mechanical connection between it and the lens, so no 'screwdriver' auto-focus. AF is done by electronic control of the lens' built-in motor.

Fine - but then how do lenses such as the Tokina 12-24 and 80-400, which, as far as anyone seems to know, do _not_ have built-in motors, do AF on Canon AF bodies?

If the Canon-mount versions of these lenses _do_ have a built-in motor, then they are entirely different lenses internally from the Nikon versions, not just different mounts. This seems unlikely.

Is a puzzlement.

[tim]

If the lens doesn't have a motor, it's manual focus. There are big differences between lenses for different mounts - the optics are the same, but electronics and drive are apparently quite different.

[CyberDyneSystems]

The third pary manufacturers lenses DO have built in motors for the Canon mount,. and some other mounts as well. Even Nikon's most recent generations of AF lenses has moved the motor into the lens.

As "unlikely" as it seems ,. it is true that the lenses by third parties for Cameras of different manufactures are contructed VERY differently.

However,. most third party lens manufacturers use focus motors in there lenses that are dog slow.. with the only exception being Sigma's "HSM" focus motor on many of there EX series lenses.