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Canon EOS lenses
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Canon EOS lenses

by Hfuy on Sat Nov 27, 2010 9:31 am

I have long idly mused that I'd quite like to be able to control the aperture of Canon's EF lenses when they're mounted on non-EOS cameras.

Physical practicalities of the lens mount adapter aside, we know that Canon EF lenses communicate with the camera using SPI, and although the command set is proprietary, it could probably be reverse-engineered by observing communication between a camera and lens. People have done this before, and there's reportedly a few subtleties in the communication, but I suspect it'd be quite possible to make it work for a given subset of lenses, if not for all lenses.

Does this sound like an Arduino sort of a project? What would I need to do in order to make one sniff an SPI bus and send a report of observed traffic to a computer for logging and analysis?
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Re: Canon EOS lenses

by adafruit_support_bill on Sat Nov 27, 2010 10:29 am

There is a thread on this topic over at the CHDK forum: http://chdk.setepontos.com/index.php?topic=1331.0

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Re: Canon EOS lenses

by Hfuy on Sat Nov 27, 2010 11:00 am

Yeah, I've seen that. There's a few "is anyone interested in this" threads kicking around, but not many with much hard info. I'd assumed it would be a start-from-scratch scenario, with maybe a few fragments of intelligence gleaned from threads like that.

I have looked at Bus Pirate, which seems to be designed for situations just like this, but the thing seems to suffer quite badly from "coder documentation" and having perused the manual I'm still not clear on whether it'll sit on an SPI bus and report all the comms that go in both directions or, if it will, how to make it do that.

P
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Please be positive and constructive with your questions and comments.