I found an Olympus OM 28mm 3.5 at my local Goodwill for $5, so I obediently bought it. I'm not sure how these lenses work, though. It's got a nice clicky aperture ring, but there doesn't seem to be any way to keep the aperture set at the desired setting, unless you depress a small, spingy button on the barrel near the lens mount. I can't seem to switch the lens to a manual aperture mode. Looking online for adapters, the ones I found don't seem to have aperture settings, so my question is, how the heck do I select aperture if I mount this lens on an adapter?