Does anybody know if OM lenses rest wide open, or rest at set aperture?
Seen a OM tilt adaptor to EF-m, just windering about practicalities (i.e. am I stuck wirh a wide open aperture always, or can I control it, I know there is an aperture ring on less, I just recall someting anout the shutter being cocked bon OM bodies)
With my cheap OM to EOS adaptor (no chip; purely a mechanical piece of machined metal), there's a little screw/pin in the right place, so that the OM lens stays at the aperture you set. So when the shutter goes, the OM lens' aperture doesn't need to change. Also it helps with metering, cos the camera has no way of knowing what aperture the lens is set to anyway, so it pretty much has to work this way.
I've used my OM lenses quite happily on both my 7D when I had it, and my 5D3 now.
This comparison I did might be of some small interest, but the only aim at the time was to discover things about which lens was fastest/brightest, and what the bokeh was like. It compares about 5 different OM 50mm lenses and the Canon 50mm f/1.4 lens.https://www.facebook.com/media/set/?set=a.4505135767033.1073741834.1849695638&type=1&l=eb457b7c51
On an OM *body*, obviously, the iris DOES move when the shutter goes. So when you're composing, it's wide-open, and when you fire, something in the body (a pin or lever, I guess) actuates the lever on the lens to stop down the iris.
In "Program" modes on OM bodies, you set the lens to the most-closed aperture you want to allow the body to use (typically f/16, the slowest aperture), and then the camera will "decide" what aperture to set the lens to when you fire, so it's more advanced in that case than just opening/shutting the iris. It also decides what shutter speed to use. I don't know what the algorithm is, i.e. whether it favours the fastest shutter speed it can get (using max aperture at the expense of DOF), cos I never use the program modes.
Back to the EOS M, I am waiting very impatiently for the high-end one to come out, which assuming I still have a job and am still alive and well enough to bother, I will probably buy as soon as I find one available. I intend to get the EF adaptor and use my 50mm f/1.8 (i.e. very small/compact) with it, sometimes. I think it'll be fun! Just bring the damn thing out, already!