Hi Bart, > As far as I know there are two different types of > teleconverters out there: the 'intelligent' ones that 'talk' > to the camera and the 'dumb' ones that don't. You can tell > them apart by checking out the number of electrical contacts > on the camera-side of the TC. If you see the same amount of > contacts on your TC as on the camera itself (about 10 or 11, > if I'm not mistaken) you have an intelligent TC
As far as I know (from discussions, tests and disassembling stuff myself), the Canon and Sigma EX TCs *do*not* have any electronics in them, so those are as dumb as it gets. It's the *lenses* with extra contacts (i.e. compatible with those TCs) that use the additional 3 contacts to detect those converters and adjust the values they report to the body accordingly. The TC just passes the information from the lens through to the body. The 3 additional contacts are just on the lens side of the converter and are used to tell the lens which converter is attached. When you attach one of those TCs to a 'dumb' lens without the extra contacts (and thus without the electronics to detect a TC and adjust to it) or tape over those contacts, you will not only get a false aperture display, but the AF is likely to 'overshoot' and oscillate around the point of focus. OTOH, the somewhat 'intelligent' Kenko 2x MC7 (and probably any other TC without the extra contacts) *does* have electronics. The displayed aperture is not adjusted, but obviously AF data are, because AF will work with any lens without oscillating significantly (provided the actual aperture is still good enough for the AF to work at all). I suspect it might introduce a similar compensation factor for the aperture data as well, but this is just a guess. I have not used Kenko Pro TCs, but I believe they have both the extra contacts and electronics for 'dumb' lenses. Don't ask me how they know which one to use. Bye, Martin * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
