http://www.nikonchat.com/nikkor-best-lenses/

What kind of lens should I get for my Nikon D40?
I'm thinking of AF Nikkor 50mm f/1.4D And what type of flash memory will be the best?
Well, since you're wanting to get a lens with a low opening, then you probably do not want an instant, right? The lowest point of openings is captured with faster shutter speeds in low light without using flash:. Therefore, if you are the decision to achieve that goal Oh, wait AUTO FOCUS NOT READ THIS IN THE D40! IMPORTANT this lens The only autofocus lenses on the D40 are "AF-S" or a very old species "AF-I." Make sure when you're deciding on a target, says AF-S, otherwise you will have to focus manually. I found two other lenses (about the type you suggest) the autofocus of the D40. nikon 50mm f/1.8D AF-Nikkor (very cheap, but still large, around $ 130) Sigma 50mm f/1.4 EX DG HSM (much more expensive, about $ 450) Hope this helps, and make sure that from now on to find the AF-S or AF-I command to find objectives compatible with the D40.
Landscape Photography Tips – David Oliver