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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

 
krb
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Feb 04, 2011 16:25 |  #46

Whether it's level of error or distance, it's still the same engineering problem with the same points of failure.


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KaiserSose
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Feb 04, 2011 16:33 |  #47
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I wish there were more projects like this.

Seems to me there was a page somwhere a Sig body was hacked to use different lenses?

And I can NOT find it, I remember ?? called a "shotgun??" Was 2 or 4 fast Nikon L lenses hacked and remotely controlled for astronomical work.




  
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ivicyrusivi
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Feb 04, 2011 17:23 |  #48

phigment wrote in post #11777803 (external link)
Well, canon lenses have a shorter register distance, so you would lose infinity focus.

And you would also need to know the nikon communication protocol as well.

krb wrote in post #11777830 (external link)
There are physical issues that would prevent this unless you wanted every lens to be a macro lens.

oh fair enough, that's a shame :(


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KaiserSose
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Feb 05, 2011 09:51 |  #49
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Here's a little food fer thought. This was some time back that someone converted a Sig DSLR body to shoot Canon EF lenses:

http://www.fredmiranda​.com/forum/topic/67585​2 (external link)




  
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astronomerroyal
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Feb 05, 2011 22:49 |  #50

I've only had a little time to log the AF communications - still some work to be done there. It doesn't look extremely complex, so I'm confident that a basic focus controller will be possible.

Before getting into these details I realised I needed to replace the extension tube hack with a modified teleconverter. This provides me access to the pins whilst maintaining infinity focus - making the rig actually useful/usable.

Unlike the Canon 1.4x teleconverter, the relatively affordable Kenko-Tokina 1.4 teleplus pro 300 allows me to mount all of my Canon EF lenses - including wide angles. No rear-element interfernce. Inside I found a simple PCB with passive components and a gate array. I made a small PCB to replace the original, providing me simple access to the communication pins. Here are some pictures,

IMAGE: http://www.thewhippersnapper.com/EF/TeleCon_mod_1.jpg
IMAGE: http://www.thewhippersnapper.com/EF/TeleCon_mod_2.jpg



  
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number ­ six
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Feb 05, 2011 22:54 |  #51

Wow! Well done - keep us posted, please...

-js


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mabviper
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Feb 05, 2011 23:25 |  #52

The pins you labeled makes it seem like their using SPI.
Based on your findings, did they modify the protocol at all?

Very interested to see what else you have in store ^^


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RDKirk
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Feb 06, 2011 00:36 |  #53

That's been my impression also, butI don't think it's just distance - I think it tells the lens, "Move this much in that direction" but that's just my hypothesis. Reading through some Canon AF materials it really does seem to calculate what the focus error is rather than the distance.

That's what can be gleaned from what Canon has said, primarily in "Lens Work III."

However, a subsequent tap should bring it closer to being correct. Misfocusing lenses seem to stabilize at the wrong spot. That's why I wondered what sort of communication had been deciphered.

Of course it would. It does not know what you intend to be "correct." Whatever point it had determined should be the focus point would still calculate to be the focus point. The only difference is that the process will be quicker the second time.


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astronomerroyal
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Feb 06, 2011 08:55 |  #54

mabviper wrote in post #11785837 (external link)
The pins you labeled makes it seem like their using SPI.
Based on your findings, did they modify the protocol at all?

The wikipedia entry for `EF Mount' gives the pin assignments and states that it is 8 bit SPI plus 1 stop bit. However, I would say it's 8bit SPI plus the lens generates a busy signal on the clock line. To accommodate the busy signal I use the SPI peripheral on the microcontroller and wrap it in functions that deal with the additional busy signal.




  
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richardfox
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Feb 06, 2011 09:11 |  #55

Absolutely incredible minds on this forum!

None of us can leave ANYTHING alone!


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astronomerroyal
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Feb 06, 2011 09:30 |  #56

A couple of remarks about the clock speed,

1). Communications all begin at about 80kHZ, but if the lens is capable of higher clock speeds, the clock may increase to a whopping 500kHz. Obviously this makes possible performance improvements.

2). Interestingly, the high-speed lenses aren't necessarily L-series; the 400mm f5.6L only runs at 80kHz, and some non-L series lenses can run at 500kHz.




  
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krb
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Feb 06, 2011 19:17 |  #57

astronomerroyal wrote in post #11787454 (external link)
2)the 400mm f5.6L only runs at 80kHz,

Yet it has a reputation for fast focusing.


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astronomerroyal
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Feb 20, 2011 14:10 |  #58

Had some luck with the focus protocols. Here are a couple of short clips demonstrating basic follow focus. These are actually time-lapse sequences; take a photo, then move the focus motor by N steps, and repeat. For now this is slightly simpler to implement than continuous focus driving when shooting video.

Focus control is significantly more complex than aperture control.

These are straight out of the camera, so ignore the set-up shots at the beginning;

Password for both is EF

slow
http://vimeo.com/20170​008 (external link)

and fast
http://vimeo.com/20168​510 (external link)




  
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yjt
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Feb 20, 2011 15:27 |  #59

godosomething wrote in post #11880065 (external link)
Password protected ...

yeah he said the password is EF... make sure they're capitalized.


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woos
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Feb 20, 2011 17:04 |  #60

Now just gotta find that secret routine:
IF SIGMA LENS MOUNTED = 1
THEN DO RANDOM FOCUS ERROR

:P


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Reverse-engineering Canon EF lens protocol
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