This is a great, I repeat great lens. It is so sharp and I have used it on both my D100 and D200. I bought it about 2 years ago, before getting my zoom 28-100 because I wanted a fast lens that could be used whilst photographing with available light. This means for those who don't know, working without any other light source than is what is available in the room, or if outside, the sunlight.
Because it stops down to 1.8 aperture, the lens can be used in low light conditions without having to keep the shutter speed really slow, thus avoiding too much shake. Ken Rockwell has a great review of this lens here if you want to learn more.
This is a Nikon 50mm lens that can be used on a film or digital SLR cameral. It has a manual aperture ring, which you can activate or deactivate as you need (if using with a digital SLR, you would normally dis-engage this feature and set the aperture via the camera).
If you're looking for a fast prime, then you would do worse than looking at this one for your low light photography needs
