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Nikon Hacker • View topic - Lens serial communication

Lens serial communication

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Re: Lens serial communication

Postby lain » Wed Nov 06, 2013 1:54 pm

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Re: Lens serial communication

Postby coderat » Wed Nov 06, 2013 1:57 pm

Do you think there is may be a number of pulses inside some bytes returned by one of serial commands ? Then cheap cams use this to get pulse number and stop AF motor, pro-bodys count pulses self and stop more exactly ?
That would correlate with a info of one photograph about using 50 1.8G on pro-body - he had much more accurate focus as I did.

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Re: Lens serial communication

Postby lain » Wed Nov 06, 2013 2:13 pm

That could indeed make sense!
While I realize it is not absolute, this patent has lots of information which turns out to be true to what we are seeing. It describes KD(1) and KD(2) bytes as part of the lens ID information in Table 2. KD(1) and KD(2) together make KD, a conversion coefficient used for AF. It explains that the amount of defocus is given by the phase-detect AF system, and then that defocus distance is multiplied by KD to obtain motor drive information.
It explains that KD is encoded as: let m = KD(1) and n = KD(2), then KD = (m/128) * 2
KD(1) is unsigned and KD(2) is signed.

It references another patent (US4509842) which indeed says that KD multiplied by the defocus distance is the number of pulses.

That patent also explains the aperture value encoding, matching what we have seen, and the aberration data and so on.
I think, since many other things in the patent match what we see, it is a very solid starting point.
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Re: Lens serial communication

Postby astronomer » Wed Nov 06, 2013 2:30 pm

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Re: Lens serial communication

Postby lain » Wed Nov 06, 2013 2:36 pm

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Re: Lens serial communication

Postby astronomer » Wed Nov 06, 2013 2:38 pm

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Re: Lens serial communication

Postby lain » Wed Nov 06, 2013 2:45 pm

astronomer, OH! I see, sorry about that. Well, our findings show that pins 5/8 are driven by the lens, not the body. Maybe it was the first of its kind to have GMR information to feed back to the body? Or am I still misunderstanding?
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Re: Lens serial communication

Postby coderat » Wed Nov 06, 2013 2:46 pm

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Re: Lens serial communication

Postby lain » Wed Nov 06, 2013 2:51 pm

coderat, speaking of bodies with 7 pins and in-body motor, a friend is sending me an old D70 he has lying around, and an AF-D lens. This should get us some more information about what is going on with pin 8, and more lens protocol info in general.
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Re: Lens serial communication

Postby astronomer » Wed Nov 06, 2013 3:21 pm

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