What is a Prime Lens?

What is a prime lens in photography? What is a prime lens used for? What prime lenses should a photographer have? You see the term “prime lens” a lot in discussions about serious photography, so I’ll be listing some thoughts on what is a prime lens and how they’re used to help you determine if you need one.

Editor's Note: Images of lenses used as illustrations are courtesy of MPB, the online platform to buy used photo and video gear.

Definition of What is a Prime Lens

What is a prime lens? Prime lens is another way of saying a lens that is a single focal length or not a zoom lens.

The 18-55mm or 24-70mm lens that came with a camera kit is not a prime lens, but a 12mm ultra-wide-angle lens, a 50mm “Nifty Fifty” lens, a 100mm macro lens, or a 400mm telephoto lens are all examples of what is a prime lens since they are single focal length lenses.

Some other terms you may notice when discussing what is a prime lens are fixed focal length or fixed lens. These mean exactly the same thing as saying they are a single focal length lens. So prime lens, single focal length, fixed lens are all describing the same thing - a lens that has one focal length that does not change.

What is a Prime Lens Used For?

With the definition of what is a prime lens fixed in our mind, let’s have a look at the question of what is a prime lens used for. Or to put it another way, why would you want to have a prime lens?

There are three reasons that are generally given concerning why a photographer may desire a prime or fixed focal length lens. Size and weight of the lens, a faster maximum aperture, and better optical performance. Let’s take these one at a time.

The size and weight of many kit zoom lenses are often not very much, many times due to limiting the maximum aperture or using lighter weight materials such as polycarbonate over metal in the lens barrel.

But once you get to looking at zooms outside of the kit lens type, such as wider angle, longer telephoto, or faster maximum aperture, many zoom lenses start to get larger and heavier. A single focal length prime lens doesn’t need to have all the elements and mechanical considerations of a zoom lens design, so they can be smaller and not as heavy.

Since the lens does not need to cover many focal lengths, this allows the lens designers to make the prime lenses with a faster (larger) maximum aperture or f-stop. Many prime lenses are substantially faster than zoom lenses having that focal length in their range, opening up creative possibilities of selective focus or shooting in lower ambient light levels.

In my experience, the faster aperture is often the most important reason photographers may opt for a prime lens over a zoom lens. So many of even the faster zoom lenses still aren’t nearly as fast as a prime lens can be. A Full Frame format 24-70mm f/2.8 zoom lens is great, but a 50mm f/1.4 prime lens is two full stops faster and allows for a much shallower depth of field.

This selective focus reason is especially evident when considering telephoto lenses for portraits. As another example, the kit zoom lens with most APS-C format cameras, the 18-55mm lens, has a maximum aperture at the telephoto end (55mm) of f/5.6 or f/6.3. By contrast, a 50mm f/1.8 prime lens has an advantage of over three f-stops!

Finally, lens performance. While most modern zoom lenses are superbly designed and have excellent image sharpness, the other lens characteristics, such as aberrations or diffraction and flare, are much better corrected in a prime lens than in a zoom lens.

Remember, it’s not just the sharpness or resolving power, but everything about a lens that determines how good your final images can be. If you’ve ever noticed color fringing or line distortion in an image from your zoom lenses, then you may want to look at some prime lenses.

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The Different Types of Prime Lenses

We could make up a huge number of different types of lenses, but I’ll stick with a few that anyone getting more serious about their photography may be interested in. For my limited list, I’ll talk about ultra-wide-angle lenses, fast normal lenses, macro lenses, and portrait lenses.

You could also include fisheye lenses, super telephoto lenses, and tilt and shift lenses, but those are pretty specialized types of lenses that some photographers will not find a need for.

Some of the exact focal lengths involved will vary based on what format you’re using. For listing some of the examples, I’m going to assume you’re using Full Frame, APS-C, or MFT (Micro 4/3rds) format cameras.

Ultra-wide-angle prime lenses are desired for their low levels of distortion. An ultra wide lens is already a bit touchy to use properly with regards to correctly rendering straight lines, so the low distortion of a prime lens design is very welcome.

Fast normal lenses can be incredible bargains for prime lenses in the f/2.0 or f/1.8 aperture range, while f/1.4 lenses will cast a little more. Lenses in the super fast apertures of f/1.2, f/1.0, or f/0.95 can be very expensive and will also be large and heavy, but there is nothing else quite like having that wide of a maximum aperture.

Prime focal length macro lenses are heavily corrected for producing a flat field of focus, extremely important for certain types of macro photography. Many of the telephoto macro prime lenses can also do double duty as a portrait lens.

A portrait lens is often a short telephoto prime lens with a decently wide maximum aperture. While macro lenses that are similar focal lengths may only open up to f/2.8, f/3.5, or f/4.0, a portrait short telephoto prime lens can often be found in the same apertures as fast normal prime lenses.

How to Choose Your Prime Lenses

Choosing your prime lenses depends on multiple factors. Mirrorless vs DSLR style of camera, what format you’re using, and what needs or wants you have concerning some of the things previously mentioned.

Price can be a huge factor in deciding on what prime lens to get, but there is an option I like to recommend that can help lower costs, sometimes significantly, namely, buying used equipment from a reputable online platform such as MPB.

It’s easy to shop used lenses from the online platform MPB since they inspect every single time they get, clearly list the exact condition of cameras and lenses, and also offer returns and a warranty on most items.

In the closing section, I’ll list a couple of examples of each of my four types of prime lenses that I found currently available on the online platform MPB. Now that you have a better understanding of what is a prime lens and how useful it can be, you can confidently look for your next prime lens.