Thank you, John. I found a useful page at

http://digilander.libero.it/aohc/selart18e.htm

giving a history of the K-mount series. Mine clearly pre-date the KA variants.

Is the route to the "firmware update" pretty clear?

I have seen the general advice that the *ist D is compatible with K-mount lenses, but I have a nagging feeling that someone somewhere has pointed out a limitation in this respect, and I have a dim recollection that it was something about not being able to use some of them in automatic mode. I have a bunch of K-mounts -- 28, 50, 85, 135, 400 -- purchased between 1975 and 1985 for use with my LX, and have been holding off going digital, hoping that Pentax would finally deliver a good product. I'd be grateful for confirmation that there are in fact no problems using such lenses with the *ist D, other than the change in perspective.