Kathleen, do you know what year your extension tube set B was made? It probably communicates all the features that were transmitted at that time. Older cameras, like the MX for instance, read out the aperture in the finder by means of a little window on the pentaprism, which looks down at the aperture ring. Naturally, that doesn't work when using an extension tube or teleconverter. Later cameras and lenses have electrical contacts to communicate with each other, but that didn't begin until 1983, with the KA series lenses.
Take a close look at the extension tubes. They'll have a mechanical linkage to stop down the lens (that's the Auto part), but probably no electrical contacts, which would be needed to transmit the f-stop info, nor a drive mechanism for autofocus. At present, I don't believe Pentax makes extension tubes which permit autofocus. Kenko makes a tube (not a set) which does allow AF. However, the lack of AF and aperture readout shouldn't stop you from happily using your extension tubes. I have an extension tube set K, probably dating from the early '70s, that works fine with my MZ-S. It has no linkages whatever, and is really just a set of tubes. Having to stop the lens down manually is an extra step, but for occasional use, I don't mind. I agree that the folks at Pentax (if it was a technician you spoke to) should have been able to tell you this, but a junior technician might have been in diapers when your tube set was made, and not familiar with it at all. Hope this is helpful. Pat White
