Do you have a prime lens? All DSLR owners should have at least one fast fixed focal length lens in their camera bag. Zoom lenses are great and can reduce weight and expense. However, when the situation calls for it, a good prime lens can be a photographer’s best friend. In the following article, you’ll learn what a prime lens is and the many ways a fixed focal length lens can enhance your photography.

Not too long ago, the average photographer avoided zoom lenses. Single focal length lenses, known as prime lenses, were faster, lighter, and less expensive. More importantly, the premium lenses offered superior sharpness and image quality.

Fortunately, lens manufacturers have been able to drastically improve zoom lenses so that their image quality is almost on par with mainstream lenses. This has been a boon for photographers, who can replace a bag full of lenses with one or two zooms. If image quality were the only criteria, most photographers could easily get by with a couple of good zooms. Of course, there’s more to lens selection than image quality, and there are plenty of situations where a prime lens is still a superior option.

Velocity

It’s usually easier and less expensive to build a fast single focal length lens, and few zooms can match the low-light qualities of a prime lens. Fixed lenses with maximum apertures of f/1.8 or larger are common. By contrast, most zoom lenses top out at f/4 or so. Even the best and most expensive zooms rarely exceed a maximum aperture greater than f/2.8. The superior light gathering properties of a good prime lens can make a big difference if you are shooting in available light indoors or after dark. It is true that you can increase the ISO to improve the ability of the zoom to shoot in low light. But a high ISO can create quality problems. When existing light is dim and you don’t want to break out a flash unit, your prime lens can save the day.

image quality

I already said that zooms have reached parity with fixed lenses. In general, the optical requirements to create a great prime lens are well understood, while zoom lenses require extensive engineering to produce excellent results throughout the entire focal length range. While there are some truly great zooms on the market, many zooms are better at certain focal lengths than others. Photographers talk about the sweet spot: the focal range where a particular zoom offers the best performance. At other focal lengths, sharpness and contrast may be affected. Again, this isn’t true of all zoom lenses, but as a general rule of thumb, it’s much easier to design a great prime lens than it is to design a really great zoom lens. So excellent primes abound, while standout zooms are rare (and expensive!)

Size and weight

Typically, a prime lens is much smaller and lighter than a zoom lens. The zoom lens requires more internal elements and there must be a mechanism to zoom those elements closer to each other. Also, fast zoom designs often incorporate very large optics to collect more light. As a result, a fast zoom is often much larger and heavier than a prime lens. This is important when you want to use your DSLR as a lightweight walking camera. The unobtrusive main lens also makes it easy to capture candids, as the lens is much less noticeable than the big zoom.

cost

A quality zoom lens will be more expensive than a prime lens, though the extra cost is somewhat offset by the fact that a single zoom can replace multiple fixed focal length lenses. Still, price can be an important consideration, especially if you’re looking for a very wide or very long lens. For example, a 300mm prime lens will generally be much cheaper than a good zoom that includes a 300mm focal length.

Faster autofocus

There are so many lenses on the market that it’s hard to make a blanket statement about the autofocus speed of prime lenses relative to zooms. Still, the prime lenses seem to focus more quickly than their adjustable focal length cousins. Part of that may again be the speed aspect, as the extra light allows fast lenses to focus more quickly. Additional elements on a zoom lens can also reduce focus speed. When the situation calls for fast autofocus, a prime lens may be a better choice.

There’s always room for a small prime lens

When packing for a photography assignment, I usually choose my lenses to save weight and fit everything in my smallest bag. Large zooms are usually the first to cut out, unless I know I’ll need them for the shoot. By contrast, my short primes take up so little space that I usually slip one or two into my camera case, just in case. If I need the lens, I’m glad I brought it, but if I don’t use it, I don’t feel like it’s a burden to have it.

You may not use your prime optics every time you shoot, but you’ll find that prime lenses offer so many advantages that you’ll want to have a different prime lens or two with you every time you venture out with your camera.