Originally posted by dadipentak Thanks but that doesn't seem right. I want AF and the adapter is supposed to deliver that (and, in fact, it does its focusing thing.) Also, it worked fine at f22 with a different lens so why not this one?
You mean you actually forced this other lens to stop down to f/22 before pressing the shutter? Simply setting the aperture to f/22 doesn't normally stop it down until the shutter is pressed, unless you're talking about a screw mount lens. And with screw mount lenses, I'm not sure the camera will refuse to fire just because focus hasn't been achieved (maybe that depends on the the setting of the custom option having to do with focus indicator and screwmount lenses?). So without knowing exactly what strings you pulled, I'm guessing you weren't really asking the camera to do the same thing at all with this other lens.
Anyhow, while the AF system of the TC may have moved the lens, and may have even achieved semi-decent focus, it may well have given up before true "lock" was achieved. And if there isn't enough light for the AF sensor *in the camera* to judge that focus lock has been achieved, it won't fire when in AF-S mode. For a lens that is presenting f/13 to the focus sensor (as I believe yours is), I'd be really surprised if it was able to judge a focus lock, unless maybe you were focusing on the sun.