I’m having fun doing something that the nikonistas on the message boards say is impossible. They say that new camera buyers should at all costs avoid the Nikon D40, the entry-level digital SLR which I happen to own, because it cannot autofocus with AF lenses. And “cannot autofocus,” to them, means “cannot use.” (The technical explanation is that the D40 lacks the autofocus motors that AF lenses rely upon, whereas AF-S lenses have their own motors.)

To which I say: horseshit. You can use AF lenses with a D40; the only thing you give up is autofocus. All the other electronic trickery an AF lens is capable of still works.

So I bought an AF 50 mm f/1.8D prime lens on Thursday — the lens that the message board types point to as the lens you want and that you can’t use on a D40. I bought it because it serves a particular purpose: low-light environments where the room is too cavernous for a flash to do any good, but I don’t have a tripod. Trade shows and museums — the sort of place I would tend to shoot.

A few months ago I didn’t even know what a prime lens was — it’s simply a lens with a fixed focal length (i.e., no zoom) — or why I’d want to pay $175 for this one. I didn’t grasp aperture or F-stops, you see, which is exactly why the D40 was the right camera for me: it’s good as a learning DSLR.

It’s proving interesting, having to manually focus. The in-focus indicator still works, see, so I’m not wholly reliant on my questionable eyes. It’s also giving me practice shooting in aperture- and shutter-priority modes. The point of a f1.8 lens is to use that big honking aperture: to let in more light or to increase the shutter speed. Manual focus renders it no good for sports photography, or quick-and-dirty shooting. It’s going to be, in addition to my low-light lens, and my portrait lens (if I ever get around to shooting those), my careful lens — a lens I use when I want to spend time thinking about composition, and when I have time to futz with shutter speed, aperture, and ISO settings.

I’ve been experimenting for a couple of days and have been having fun playing with depth of field, understanding bokeh, that sort of thing. We’ll see if it has an impact on my photography.