Finally worked out the answer to my lens question - definitively now. I
was looking at another lens on Ebay - a 50mm 1:2 H Auto and
wondered if that would meter - turns out that is an older method - the
auto has nothing to do with focussing - it just means that the aperture
ring opens and closes automatically with the shutter release.
Found this handy chart on Ken Rockwell's site if anyone's
interested. I've got a D40 and the lens I bought was AI - so that
means it will fit - the older lenses need altered to fit but everything
since then has the same mounting (although pre AI lenses will fit a D40
just due to it being a bit more compact). You can see that until
you get to AF-S or AF-I the metering and autofocus don't work.
Some of the more expensive models do meter with the older lenses
but the bodies are a lot more expensive.
If you look at a picture of the lenses you can see the difference -
the older ones have 4 or 5 electrical contacts and as they get
newer they have more and more - the most recent up to 10 - obviously
just so the lens can connect with the newer bodies.
Shopping at The Leftorium since 1977.