...millimeter, that is.
Back in the day I used my dad's Nikon S2 35mm rangefinder camera. It has three lenses: a 35mm wide-angle, a 50mm normal, and a 135mm telephoto. I used the 50mm normal lens the most. When my dad switched over to a Pentax 35mm SLR with zoom lenses I started using those. Eventually I used nothing but zooms.
I lost interest in using prime lenses. Yes, I knew that an 85mm or a 105mm lens was great for portraits, but I used a zoom that covered that focal range. Yes, I knew primes were always faster than zooms, but I didn't feel a need for a fast lens for low-light situations. And I didn't want the hassle of switching lenses: having a zoom negated that problem.
But...using a zoom in low light meant I had to increase my ISO on a digital SLR to sometimes undesirable heights. I wasn't happy with all the electronic noise as a result. So I started researching wide-angle (35mm) and "normal" (i.e., 50mm) prime lenses to use on a Nikon APS-C SLR, and finally settled on the Nikon 50mm f/1.8 AF-D lens. It was cheap and "fast" (allowed lots of light in). And with my crop factor of 1.5, the 50mm has the field of view of a 75mm lens on a 35mm film or full-frame digital SLR (which makes it act like a short telephoto lens).
Oh...and I need to remember that I have to move when I'm framing a subject.
Here are some examples using the 50mm:
I use it a lot wide open (maybe to a fault), as you can see. I focus on the eyes, and shooting with the aperture wide open causes the background to blur nicely.
It's sharp, the bokeh is nice, and with the aperture diaphragm made up of straight blades instead of rounded ones, you'll get wonderful 14-point sunstars when the lens is stopped down to f/16 or f/22. You can get one for about $125. It's being replaced by the newly-introduced 50mm f/1.8G.
(Important note: the 50mm f/1.8G AF-S will autofocus on the cheapest Nikon DSLR's (like the D40, D40X, D60, D3000, D3100, D5000, and D5100. The 50mm f/1.8 AF-D, the subject of this post, will not autofocus on the models I've listed.)