Originally posted by jenko i've heard it is a good tc, but will it work with a 70-200 f/2.8 sigma hsm?
the TC has some unique features.
First of all, it modifies the lens information for F-Stop so that the correct F-Stop is used by the camera for exposure including the 1 1/2 stop loss of the TC
Second, it does not have a pin for transmitting the lens focal length and focusing data to the body, so you will have to enter focal length, therefore for a zoom, you will need to enter the focal length you wish to use. This is because it needs that pin to control the movement of the internal elements in the TC which actually do the focusing function.
The TC does not have the power pins of the KAF2 mount.
So with respect to HSM lenses, it will function as it does with MF lenses, you focus close with the lens focusing collar, then let the AF elements in the TC do the rest.