For most people, the initial foray into getting serious about photography involves getting a lower end “prosumer” DSLR camera with a kit lens. The images produced by such a setup can be extremely good and there is nothing wrong with sticking with that gear. Some photographers, however, might start to wonder what else in out there in lens land and many will start to contemplate lenses with different focal lengths and other will consider a prime lens. Let's take a look at why you would consider the prime lens option.
What is a Prime Lens?
Quite simply, a prime lens is simply a lens with a fixed focal length. Sometimes they're called “Primary Focal Length” or “Fixed Focal Length” lenses.
Note: Sometime's there's a little confusion as the term “Prime Lens” can be used to refer to the primary lens in a combination lens system. For this article we'll be talking about them in their fixed focal length meaning.
What Are the Advantages of a Prime Lens?
A prime lens can be great for a lot of reasons. For starters, the optical performance of prime lenses is usually a lot better than zooms as they are built to specialise in their single field of view. That means that they most often have a much wider maximum aperture setting than other lenses. This makes them perfect for shooting in lower light situations (bars, clubs, concerts) and also for getting a limited depth of field (great for portraits for example). The fact that you can open up the aperture so far also means you don't have to resort to flash as much.
The other big advantage is that prime lenses are usually smaller and lighter than zooms, which can mean a lot to those of us who like to shoot for extended periods and sometimes get weighed down by our gear.
What Are the Disadvantages of Prime Lenses
Basically prime lenses are not as versatile as zooms. You have to use your feet (ie move your shooting position) in order to get the exact image crop that you want. This isn't necessarily a bad thing (in fact it's good to practice composition with your feet rather than lens or in post production), but in certain situations it can be an irritation. Other than that, there isn't a lot of downside to primes.
What Prime Should I Get?
This really depends on what you plan to be shooting.
Traditionally, on film cameras the 50mm prime lens held pride of place as it was the lens that most approximated the field of view of human vision. With the advent of cropped sensor DSLR cameras the 35mm focal length prime lens is the standard for that.
On the other hand, the fastest prime lenses for DSLRs are in the 50mm range. The 50mm f/1.4 lenses for both Canon and Nikon are great lenses. Even the cheaper Canon and Nikon 50mm f/1.8 lenses are great (and very cheap). The 50mm is still the most popular prime lens.
If you plan to be shooting a lot of portraits, then you might want to go with a focal range closer to 85mm which is hugely popular among portrait photographers. If you want to shoot birds, then the 300mm prime is where you will want to start looking. This really depends on what you will want to be shooting.
As a general guide, look back though your images taken with your zooms or kit lenses and look at what focal lengths you used for the majority of your images. That will probably be a good place to start for looking for a fixed focal length lens.