davidc wrote:Does your OM glass not fit on the OM-D body? I think I'd assumed it would (in the way EF fits today's mounts)
They are completely different mounts. One is for manual focus full frame, the other for autofocus and a much smaller sensor with a 2x crop factor. It is possible, but requires an adapter and the effective doubling of focal length is a mixed blessing.
Different companies solved the issues brought about by autofocus in different ways, requiring as it does communication between the camera body and lens. Olympus more or less ignored it, by dint of bypassing the problem until digital came along. Minolta had a mechanical linkage and Canon went the whole hog by introducing the EF mount with electronic contacts to replace its previous FD one. Technically that was the best solution, but it must have hacked off a lot of customers. Nikon went for a halfway house and managed to preserve the F mount, which means that many legacy manual focus lenses can be attached to modern cameras. I am hazy on the details, but I know that Nikon has some compatibility issues with later lenses, depending on whether or not the AF motor is in the lens or the camera body. Pentax did something similar to Nikon and has retained the K mount it introduced in the 70s.
I shall be shortly be publishing the second part of my blog post, in which I came to an unexpected conclusion. Well, it certainly surprised me.