Lenses are the most important accessories for your DSLRs, and in ideal condition the body is upgraded while most people hold on to their arsenal of lenses. If we were to classify the lenses, two broad categories would be
1. Prime lens
2. Zoom lens
Prime lens is simply a lens that cannot zoom from one focal length to another; in fact, prime lenses are often referred to as a block lens or fixed focal length lenses. A simple yes and no, might not be the best reply, I started shooting with a 50mm f/1.8, and next I moved to a 35mm f/1.8 as my walk around lens, and very recently procured a 24-70 f/2.8. I definitely have a soft spot for a prime, but a fast zoom is another important investment you have to make at one point.
Most people I know prefer a zoom lens over a prime lens, well it does have its advantage of covering vast number of focal lengths without the photographer having to move, and over the years I have really cursed not having a telephoto lens (I would prefer a prime here as well) to capture a number of photographs.
Why would you choose a prime lens?
Let us compare a 50mm f/1.8 with a 18-55mm f/3.5-5.6 as both of them are two of the cheapest lens Nikon has to offer. When I say 18-55 f/3.5-5.6, what it means is the aperture is f/3.5 at 18mm (wide end) and f/5.6 at 55mm (tele end). The only advantage you have over a 50mm is the option of variable focal length, on the other hand if you were to have a 50mm f/1.8, you could have a very shallow Depth of Field, the images will be exceptionally sharp (when compared to the zoom), and you can use the lens in a low light situation without having to crank up the ISO to a very huge number. Oh and not to mention they would focus so much faster.
Are prime lens sharper than zoom?
I think in most case the argument holds true, but not completely. A prime lens is definitely sharper than a cheap zoom lens, but many of the pro level zooms, are pretty much on the same level as a prime. I personally find the 50mm f/1.8 acceptably sharp, but if I compare it with the 35mm, the latter is on a whole different plane. More often than not we hear that “prime lenses are sharper” and somehow expect that to mean that ALL prime lenses are sharp, and that simply isn’t true.
So Prime or Zoom?
When it comes down to which lens to buy, the fact is that it depends greatly on the lens. For example, I would recommend that a beginning photographer purchase a 50mm f/1.8 lens, but after using the Nikon 24-70mm f/2.8 lens for about a month now, the 50mm lens cannot approach the optical quality of the latter; however, the 24-70 is significantly more expensive.
When it comes to the prime vs. zoom lens debate, the real answer is that it depends on the lens. I just want to bring to your attention the advantage and disadvantage of the two families of lens and also to point out that the simplistic “primes are better” mentality is simply outdated.