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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 11 Dec 2010 (Saturday) 17:22
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Reverse-engineering Canon EF lens protocol

 
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Dec 12, 2010 04:31 |  #16

Very cool stuff. If you publish, I would be interested in seeing your stuff strictly for my own edification.


bodies: 450D; 600D ~ lenses: Vivitar 35mm f/1.4; EF-S 60mm f/2.8 Macro; EF 100mm f/2.8 Macro; EF 200mm f/2.8L II ~ strobes: Sunpak PZ42X TTL; Orbiter F400 BTS ~ support: Manfrotto 055XPROB + 804RC2

  
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mikiort
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Dec 12, 2010 11:06 |  #17

This is a really interesting project. I actually though that the communication protocol between a camera body and a lens is suppose to be relatively short and simple.
I mean, the camera has a microcontroller, working as a “master” and a lens has another microcontroller, working as a “slave”. Camera suppose to send relatively simple commands and receive simple answers and all the complexity of operations is suppose to be inside of each system. Otherwise it would be impossible to keep versatile.
The only thing I can’t understand why cameras never can (or would) display the third party (Sigma, Tamron…) lens information in the pictures Exif information?


Canon 5D Mark III, Canon EF 50mm f/1.8 II, Canon EF 24-105mm f/4 L IS USM, Canon EF 135mm f/2L USM, Tamron SP 150-600mm F/5-6.3 Di VC USD, Canon EF 300mm f/4L IS USM, EF 1.4x III

  
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Green_Tea
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Dec 12, 2010 11:25 |  #18

Erik_L wrote in post #11437106 (external link)
+1 for the electronic follow focus. Also, the reverse mounting macro-ma-bob requires no engineering at all, it just connects the pins to wires and then re-connects them to another set of pins. That price is stupid - high for how simple it is.

Yeah... this much more elegant solution did not occur to me:o
That price is crazy, give me two 12mm tubes, a reverse mount adapter, some wire, and 2hrs i expect that I could come up with one. Follow focus would be cool and useful.


6D|7D| Sigma 50mm 1.4 EX| Canon 100mm L IS macro| Canon 24-70 II L| Canon MP-E 65| 600 EX-RT| MT-24EX

  
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jetcode
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Dec 12, 2010 11:31 |  #19

Why not use one of the incredibly inexpensive Microchip development boards instead of prototype hardware which will eventually be taken apart? Everything I work on these days is on development boards.




  
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bkcorwin
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Dec 12, 2010 16:26 |  #20

Would love to read specs on the protocol. I have a bunch of 18 series pics and various arduinos looking for a project.

Post up I say.




  
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NeutronBoy
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Dec 12, 2010 17:01 |  #21

JeffreyG wrote in post #11435345 (external link)
You do not have any 'proprietary intellectual information' so far as I can tell. You have the results of your own experimentation. I don't see what Canon can do to you if you publish it.

Are you a lawyer?


5D Mark II, 40D, 350d
Canon 70-200 f2.8 IS II L | Canon 100-400 IS L [COLOR=black]| Canon 24-70 L | Canon 100mm Macro f2.8 | Canon 50 f1.4| Canon 10-22 | Canon MP-E 65 | Rokinon 14mm f2.8 | Sigma 17 - 70 macro
MT-24 & 430 flashes | other junk

  
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mabviper
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Dec 12, 2010 18:26 |  #22

Good project ^^ Maybe you can work on reserve engineering the flash protocol, lol.
I've been meaning to start on that but I still have master projects and exams :(

Anyways, good job ^^


7D | 15-85mm IS | 30mm f/1.4 | 50mm f/1.8 | 85mm f/1.8 | 580EX II | 430EX II | YN-560

  
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AntonLargiader
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Dec 13, 2010 05:44 |  #23

What have you seen, communication-wise, about focusing and focus confirmation?

I'm curious about why lenses can be out of focus when the camera thinks they are in focus.


T2i . 18-55 IS . 70-300 IS USM . 70-200 2.8L IS . 28mm 1.8 . 100 Macro . 430EX II . TT1/TT5 . Bogen/Manfrotto 3021 w/3265 ball-mount

  
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astronomerroyal
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Dec 13, 2010 14:16 |  #24

Sorry for the brevity of this response but I lost my previous, more detailed one.

Phreeky, the communication protocol is not RS-232 'serial' that you find on computers, it's more like SPI, designed for intercommunications between ICs.

The follow-focus idea is good. I was able to move the focus motors, although I didn't get around to achieving fine control. Aperture control was my original goal. Will definitely revisit the focus motors.

Mikort, I don't use 3rd party lenses very often, but the lens has a unique model number that it sends to the camera. You can see some basic lens specs if you open a .CR2 raw file with a hex editor. Addresses around 1878-ish give focal lengths, and what I believe to be a lens ID number. If the camera body doesn't have this lens ID number in its tables then it won't generate the "EF 17-40mm f/4L USM" string that you also see later in the exif data. I suppose you can't force Canon to fully acknowledge 3rd party exif data. The pdf I link to in the first post seems to suggest Canon want nothing to do with 3rd party manufacturers.

Mabviper, reverse-engineering the Speedlite protocol is an interesting and unusual suggestion. What were you going to do with that?

AntonLargiader, I can take a more detailed look at the focus communication. Not sure the lens has much to say about focus. Somewhat relatedly, the `AF confirmation adapters' you see on e-bay probably just mimic the presence of a lens, fooling the camera to go through its own motions.

In terms of applications, I see three classes:

1). Gadget + EF lens. Allows one to use the lens on non-Canon body, astro CCD, RED One camera (Birger mount).

2). Gadget + Canon body. The basis of 3rd party lenses, and those E-bay 'AF confirmation' mount adapters.

3). Gadget + EF lens + Canon body. Gadget intercepts/filters/mod​ifies data.




  
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mabviper
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Dec 13, 2010 14:27 |  #25

Hehe, it's interesting indeed.

I'm gonna see if I can come up with a way to control 3rd party manual flashes w/ the built-in flash settings. Although, this would require extensive electronic modifications of 3rd party flashes.


7D | 15-85mm IS | 30mm f/1.4 | 50mm f/1.8 | 85mm f/1.8 | 580EX II | 430EX II | YN-560

  
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LiberationFrequency
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Dec 13, 2010 14:36 |  #26

Your completely in the clear with this - there is nothing wrong with just figuring this kind of stuff out. If you start producing commercially stuff with this kind of information however, thats a little different. As information, there isn't anything to hide. You aren't infringing on anything until you start making money off of it.




  
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woos
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Dec 13, 2010 16:27 |  #27

Nah, in this case you're fine using it to make money as well. Sigma/Tokina/etc do NOT pay Canon any royalties or license the mount in any way from Canon.

As long as he reverse engineered the protocol, you are 100% in the clear. You could even implement your own version of it in your own cameras (like sigma does, they use the EOS signalling!) This is fine.

There is tons of legal precedent for this in the United States, as well. In other countries, I have no idea.

What would not be okay: if canon licensed the EOS protocol to you for something and then you published it or used it without permission.

What the op has done: clean room reverse engineering. Now, if the OP has somehow gotten access to information from Canon, or seen information on the EOS protocol from canon documents, etc, this doesn't apply. However, if he did a clean-room reverse engineering of the protocol by himself, without access to any info from Canon, he is 100% in the clear. That includes making compatible stuff and selling it. :) There may be restrictions on what you could call your stuff though. A lens that said "100% eos compatible" would probably be not okay, but "fits canon EOS mount" would almost certainly be fine. This isn't a grey area. Canon's marketing or HR people may tell you different, but if you get a reply from a lawyer from Canon USA they will confirm this (or beat around the bush and not deny it).


amanathia.zenfolio.com

  
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CheshireCat
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Dec 13, 2010 17:03 |  #28

Very interesting. Subscribing.


1Dx, 5D2 and some lenses

  
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Fureinku
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Dec 13, 2010 17:08 |  #29

if i keep reading this or stare at that picture any longer, my head will literally explode. Out.


Gear List | Wish List |

  
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AntonLargiader
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Dec 13, 2010 17:24 |  #30

astronomerroyal wrote in post #11445271 (external link)
Not sure the lens has much to say about focus.

What about the whole 'get the lens calibrated to stop the front-focusing' thing? I don't understand it either, but it seems to be real.


T2i . 18-55 IS . 70-300 IS USM . 70-200 2.8L IS . 28mm 1.8 . 100 Macro . 430EX II . TT1/TT5 . Bogen/Manfrotto 3021 w/3265 ball-mount

  
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Reverse-engineering Canon EF lens protocol
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