Don Weiss wrote: ------- snip ------- > Canon engineers faced a decision to make the extra contacts work > in one of two different ways. I don't know which way they chose, > so I list both of them here.
> 1a) The extra contacts on the extender tell the lens that an > extender is present, and what strength it is. The contacts are > merely wired in some pattern of (ground)/(logic high)/(open > connection) that code the information. > ..... > 1b) The extra contacts on the extender are used to reroute an > alternative output data stream from the lens. Each output stream > is already formatted for one of the (existing or planned) extender > magnifications. In this case the lens is unaware that it is mounted > on an extender; it is merely designed to output three alternative > data streams simultaneously under all conditions, and the extender > chooses which one to route to the camera's data input connection. ------- snip ------- Hi Don, i think, Canon decided for option 1a) On Canon-extenders the three contacts have only connection to the lens. - If all three pins are connected, the lens thinks that a 1.4xTC is present. - If the middle-pin of the three is not connected with the oher two, the lens thinks that a 2.0xTC is present. - If no connection between all of the three pins, the lens thinks that no TC is present. Two options I was not able to check: What happens if only the middle pin is connected with one of his neighbours ?? Regards Jochen -- GMX - Die Kommunikationsplattform im Internet. http://www.gmx.net * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
