Aperture control for canon EOS lenses on Panasonic GH2, AF100, Sony FS100 or similar
Here’s a trick I use to control aperture on Canon EF and EF-s electronic lenses when they on micro 4/3rds mount or Sony mount. You need a Canon DSLR body – while the lens is attached set the aperture. While holding down the DOF preview button detach the lens. Normally the aperture defaults to wide opens but now the aperture stays set after the lens is off.
There are other adapters out there that provide a 2nd iris which sits between the rear element and the sensor. I’m not crazy about them – feels like a recipe for aberrations! But it may be more practical for some shooters who change aperture a lot. In filmmaking I tend to choose my dof and leave the aperture alone. The technique described above is great if you want top performance from the lens and you are not in a rushed environment.
During a conversation on dvxuser I learned that detaching the lens while the canon body is in movie mode (rebel) or live view (7d/5d) will also lock the aperture. I didn’t know this as I usually leave them in M, Av or Tv (I shoot stills as well).
Its worth pointing out that these lenses were designed to have their apertures at an open position to protect them from movement when the lens is not in use. If you are switching lenses on a lot on a video shoot be aware of what aperture they are on when you finish.
Stealth mode GH2 incognito with an EF 85mm f1.8