Canon EF-S Protocol and Electronic Follow Focus

Awesome! Will come in handy…

Pick and Place

Two years ago, I spoke with a film maker who told me about the problem of manual focusing with the video enabled Canon DSLRs. As the focusing sensor works only when the camera’s mirror is down, when in video mode, with the mirror up, the camera switches into manual focusing mode, via the lens focusing ring. Several solutions exist on the market, but they mainly use mechanical links to deport the focus ring to more accessible place on the camera rig.

Some electronic solutions exist, but they use the Camera’s USB input and the focusing speed is quite low.

I decided to dig into the communication protocol between the camera body and the lens.

Canon EFS lenses are connected to the body via a 7 pin connector. Three for the power supply and four for a standard SPI serial interface (including digital ground).

Canon EF-S Connector Pinout

Then, I bought a lens extender to…

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