Why should I buy a 50mm prime lens? My kit lens is 18-55mm!
One interesting question I got recently after my recommendation video of "I just got a new DSLR camera, what should I buy next" was that someone asked why they should get a 50mm prime lens when the kit lens that came with their DSLR is 18-55mm so therefore already covers the 50mm focal range. My answer to that is NEVER question my recommendations! Im just kidding of course but seriously though there are great benefits to owning a 50mm prime even if your kit lens covers that focal range. Myself I own at least 3 lenses that cover 50mm or near to it but I still have my beautiful Canon 50mm f1.2L lens which I use all the time for weddings and portraits etc.. Why?
Well for one the image quality from almost any prime lens (a lens that has a fixed focal length and does not zoom) will be sharper than any zoom lens. Especially a kit lens that comes with lower end DSLR's.
Not to say they are no good, I used a kit lens many years back when I first started out shooting "professionally" (by professionally I mean doing photography full time as my job) but I was actually no where near pro photographer level at that stage but you've got to start somewhere.
Another advantage of a 50mm prime lens is the aperture. On a prime you will have a much "faster" aperture then on your kit lens. Generally a kit lens aperture will range from f3.5 at the wide end to f5.6 at the telephoto end where as a prime lens will generally have a maximum aperture of f1.8 on the cheap end to f1.4 for a decent quality one, right up to f1.2 or f1.0 for the high pro lenses. Some extreme primes even open up to crazy apertures like f0.95 but thats getting really geeky and expensive.
Other advantages of having such a big aperture are you are able to shoot in lower light conditions as that big gaping hole in the lens will allow the sensor to gather light much easier then a smaller hole at f3.5, f4 etc.. And in turn being able to use shoot at f1.8 or wider also means shallower depth of field. That is when you can get those shots where your subject is isolated against a very out of focus background, also referred to as the bokeh. Shooting wide open like this does have its own problems though, mainly focusing which can be super tricky when all that's in focus is just a few millimeters. Therefore you do have to be critical with your focusing making sure to just get the eyes in focus if shooting a portrait. You would not want to just use all focus points and let the camera pick what it wants to focus on because most of the time it's not going to be spot on where you want it.
Finally another good reason to get a 50 is because it will help you learn composition better because your not able to just spin the zoom ring to compose but it forces you to take the time, move around and think about how you compose your image more. You will find the look of an image made with a prime lens is quite different from using the same focal length on a kit lens, especially when used wide open. So if you don't have one already be sure to pick your self up one. It does not have to be new. There are lots of good places (at least here in Japan) where you can pick up quality used lenses much cheaper then their new versions. But for something like the Canon or Nikon 50mm f1.8 they can be had new for for as little as $100 so there's no excuse.
Canon EF 50mm f/1.8 II Camera Lens
Nikon 50mm f/1.8G AF-S NIKKOR FX Lens for Nikon Digital SLR Cameras