What's a "prime" lens and why should I have one?

Today almost every lens that comes with a digital camera is a zoom lens. It can change its angle of view to get more into the photo (that's a wide angle) or make subjects look bigger and closer (that's a telephoto).

Here's a Nikon camera fitted with a 50mm f1.4 prime lens.

A prime lens has a fixed focal length. It doesn't zoom. But because it doesn't zoom it can give you four benefits:

The Benefit of Smaller Size

An 18-270mm zoom lens, small as it is, is a lot bigger than a fixed-focal length lens.

The Benefit of Fast Glass

A ‘fast lens’ or a lens that uses ‘fast glass’ is one that has a larger aperture opening so it is capable of capturing light at a faster shutter speed than a lens with a smaller aperture. The term ‘fast’ is sometimes debated as hobbyists might consider an f/2.8 lens to be fast whereas some professional photographers consider an f/1.4 lens to be fast. A lens made with what is considered ‘fast glass’ can be a real asset when shooting in low light conditions, especially if you wish to forgo flash.


There is a budgetary consideration (read: it costs more) when purchasing fast glass, so evaluating how often you will be in the position to need this extra benefit is important. Many people who shoot in the field, in specialty situations such as evening wedding receptions, and in varied conditions find the investment to be well worth it because they capture countless moments they might otherwise miss. If such conditions impact your ability to earn money so that you can properly handle these situations, adding a fast lens to your kit might be the one tool that boosts your portfolio and client list.


The Benefit of sharper images


As good as most zoom lenses are today, the best prime lenses can be even sharper. The zoom lens that comes with your camera was designed to cost only about $100 when sold with the camera - a remarkable bargain but not the highest quality.


High-speed lenses even focus faster than others, a real plus in low light.


The Benefit of a fuzzy background


When used wide open - around f1.8 or f1.4 - a lens has much less depth of field than a lens set to a smaller lens opening. Zoom lenses usually have a maximum aperture of about f5.6 when set to a 50mm focal length. The fast prime lens can really throw the background out of focus, concentrating the viewers' attention on the subject.