I am searching for a fast AF zoom-tele lens for my D70. Will the Nikkor 80-200mm f/2.8 D ED AF lens focus as fast as the Sigma 70-200 f/2.8 EX APO IF HSM AF lens? I am also considering the Sigma 100-300 f/4 IF HSM but am leaning towards the faster f/2.8 lenses. Any answers or suggestions would be appreciated.
In general, Nikkor AF-S lenses will focus faster than AF lenses of the same focal length. (Wide angle lenses normally focus faster than teles because the teles have to move farther.) The AF-S lenses have the focusing motor built into the lens. The AF lenses use the motor in the camera through a ''screwdriver'drive mechanism in the lens mount. I can't comment on how the Sigma USM lenses compare to the Nikkor AF and AF-S - maybe somebody else can do that.