Canon EF lens mount aperture question

[loccdor]

Can someone tell me if I stop down a Canon EF mount lens on a native camera, disconnect the lens and mount it to another camera with an adapter, will the aperture blades stay closed at that selected aperture?

Thanks

 

[koraks]

No, they won't. The aperture is electronically controlled. It only stops down when taking the shot and when using the DoF preview function.

Edit: a little more nuance and some empirical information:

The first stage of the process in principle works. Take an EOS camera, set a slow shutter speed or bulb, open the shutter and remove the lens. The aperture will remain stopped down to the value that was set for the exposure. So far, so good.

The next stage is the tricky bit. As soon as you mount the stopped-down lens onto another EOS camera, as soon as the camera has power (it doesn't even have to be turned on), the lens will open up as it's apparently (and logically) part of the power-up sequence of the camera to open up the aperture on the lens installed.

The process may work if the 'receiver' camera somehow doesn't have aperture control - which may be the case you have in mind, so then it's worth a shot.
What I do not know and have not tested, is whether the lens autonomously opens up its aperture upon power-up. This is quite possible, in which case you'd have to ensure that the lens remains powerless during/after the 'transplant'.