AF in aperture priority
I'm new to manual controls, having never before used even a point-and-shoot that had PASM modes. I'm using an Olympus E-420 (with 14-42mm kit lens) loaned to me by a friend, and I've encountered a confusing issue involving AF in aperture priority mode.
I noticed that with autofocus enabled, it was as if I was in program mode - it doesn't matter what I set the aperture to, autofocus completely overrides it, and will set the aperture on the opposite end of the focus range as I set it on the camera, if necessary to focus. I did a little experimentation, setting the aperture to f22 and pointing the camera at an object only a few inches away from the camera. The camera refocused, but the display still quoted f22 with a shutter speed of 4 seconds. So I press the shutter, it snaps for a fraction of a second, and I get a clear-focused shot of the object only a few inches away from the lens. Even more confusing, I switched to playback mode, and viewed the picture info - it still said f22, 4-second exposure time.
I also did a test in reverse, zooming to 42mm, setting the aperture to f5.6 (maximum available for that focal length), and focused on an area several hundred feet to several miles away. Again, autofocus took over, focused on the distant objects, but the display (both in-viewfinder and LCD) quoted f5.6 with a fraction of a second, and so on.
Is this normal? If so, what's the difference between Av mode and Program mode?