Bart Kupers wrote... > >Hi Martin and list, > >>> 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 > >Well, up until now I thought I had figured it all out, but I have actually >never really looked at the contacts. Yesterday I did just that and Martin, >you are right: my camera's (300/5/RT) all have 8 contacts. My lenses >(tokina 20-35; 28-135IS; 50/1.8) have contacts that exactly match the >contacts on the camera (7 contacts in total, but one contact is bigger than >the others, so it actually shorts two contacts on the camera side. Only my >70-200/4L has three additional contacts. My Tamron MC7 TC has only 8 >contacts, on both sides. > >Is there anybody on the list who has disassembled his Canon 1.4x and 2x >extenders? I am VERY curious as to how these three additional contacts in >these extenders are wired. Maybe the extenders just links two of the three >contacts, depending on wheters its a 2x or a 1.4x??? If this is the case >why did Tamron/Kenko go through all the trouble of designing the >built-in-electronics, instead of just using the three dedicated contacts? >Patent reasons? > >Regards, > >Bart >
WARNING--I've got my propeller beanie on, and it's spinning at full RPMs. Now, here goes. The objective of all extender designs is to be 'transparent' to the camera; that is, for the lens+extender combination to appear to the camera in all respects like a lens designed ab initio at the effective focal length and aperture of the combination lens+extender. (I think a better term for the extender would be 'invisible' <)B^) Now, there are in principle, there are two basic approaches to the electrical design of an extender: 1) passive, i.e., no electronics, and 2) active, i.e., with some kind logic chip on board. 1) Passive. This means that the extender has only contacts in some arrangement which, in cooperation with special features of lenses designed for extenders, make the lens+extender combination transparent (in the sense mentioned above). This of course is the reason that specific lenses that Canon designates as 'extendable' have the extra contacts that mate with the corresponding extra contacts on the lens side of Canon's extenders, and those which directly copy the Canon design. (By the way, they could have put the extra contacts on the camera side and made the camera do all the work.) 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. The lens 'wakes up' when it sees power. This will happen either when the lens is mounted on the already-mounted extender, or when the lens+extender combo is mounted on the camera. When it wakes up, the lens recognizes the extra contacts, decodes them, and subsequently modifies everything it tells the camera in regard to focal length and aperture. Additionally, and if the lens designer sees the need for it, the lens can modify its response to commands from the camera, such as the amount it racks the focus in response to a focus advance/retard command from the camera. 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. Note that the lens designer has done considerable work on the lens chip's firmware in both cases 1a) and 1b). Considering the communications protocol (clocked bidirectional serial), the facilities available on the controller chips in camera and lens, and the potential functional advantages of approach 1a), that's the one that I think Canon chose. Sorry Bart, I don't know the coding of the contacts. For completeness, there's another 'passive' approach which I guess we can call 1c). This is where there are no extra contacts, no electronics in the extender, no nothing <)B^). Everything is passed through in both directions without modification. I believe the earliest 3rd party EOS extenders were like this. Of course, the camera thinks that the lens of X FL and Y aperture is still X FL and Y aperture, and autoexposure and autofocusing are hosed as a result. 2) Active. Here, there are no extra contacts needed anywhere. The logical job of the extender is to fool both camera and lens into thinking it's not there--i.e., to make itself 'transparent' (invisible). In order to do this, there has to be a logic chip of some kind inside the extender which can intervene, in real time, in the data stream from the lens to the camera, and perhaps from the camera to the lens. In the data from the lens to the camera, the chip adjusts the reported aperture and focal length values as they come out of the lens. I am assuming that (as mentioned before) the communications protocol between camera and lens is what microcontroller designers call 'clocked bidirectional serial,' or what Motorola named 'SPI' (Serial Peripheral Interface). This defines the actual waveforms and timing relationships of the clock line (from camera to lens) and data lines (both directions). The camera and lens designers then define a protocol on top of this, which states the structure and meanings of the bit streams in each direction. Now, the characteristics of this interface make it easy to define a protocol that would make it difficult to impossible for an intervening logic chip in the extender to successfully modify the data bits 'on the fly' in either direction. (I will refrain from the final level of technical detail on why this is. It would almost double the length of this note, which is too long already.) Therefore, the Canon protocol designers would have to take some care not to deprive some hypothetical active extender of the potential for full capability. Bear in mind that Canon's own extenders and long L- class lenses use the extra-contact passive approach. So if an active extender (as Martin describes the Kenko MC7) is capable of full function, it implies that the Canon designers took some care when defining the original EF lens protocol so that a full-function active extender would be possible. Or maybe they just got lucky :^). It may be that Canon's own long-L and extender designers saw the possibility of of a full-function passive extender by providing the extra lens-extender contacts. Since this approach is independent of the basic camera-lens protocol, it could have been thought of afterward. As to why anyone would build an active extender, it allows the full- function use of the extender with lenses without the extra contacts-- i.e., more than just the long L-class line. Not only that, but such extenders are in principle stackable. But it can be full-function only if Canon really did design the protocol in the way I described in the preceding paragraphs. ---------------------------------------------------------------------- As regards patent issues, Bart, there are certainly numerous aspects of the EOS EF lens interface that are covered by Canon patents. In addition, the protocol itself seems to be a trade secret. I don't know if your average third-party lens maker has to obtain a license from Canon to make EF lenses; Canon may have decided to grant free license for the basic mechanics of the interface, or they may get a license fee from the third parties. I don't know. It has been reported on this list that one third party (Tamron?) has paid Canon for access to their protocol definition; this is supposed to have the result that Tamron won't get blind-sided by Canon's exploitation of unnoticed nooks and crannies of the protocol. That is what befalls a reverse-engineering third party such as Sigma. Even Canon has to be careful about those nooks and crannies, otherwise they could break the vaunted compatibility across the EOS camera body and lens lines and become like N1k0n <>--<)B^) DGW * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
