I'm looking to adapt my Canon EF mount lenses for other mirrorless mounts. Not all of them are made by Canon (some are Sigma lenses). I'm not really interested in keeping autofocus; a mere spacer as an adapter would suffice.
The problem with adapting the EF interface is the lack of mechanical aperture control. In order to control it, you've got to use the electrical interface. To adjust the aperture one can use an Canon EOS body and dismount the lens while holding down the DOF preview button. This is a very cumbersome method though and something like a battery powered EF lens cap with aperture adjustment would be very useful. That could then be used together with passive adapters for many different mounts.
Are there anything like that available? I know there are adapters like Metabones for sony. However they are very expensive (due to being autofocus capable) and have a very limited compatibility (especially with third party lenses). I recon that if one would limit the function of the adapter to only be able to change aperture, compatibility would be easier to achieve.
Are there anything like a lens cap with aperture control (and wide lens compability) for the EF mount?