By Roger (7 December 2014)
If you have just begun with your photography, odds are you're using a zoom lens, instead of a single focal length, prime lens. And why wouldn't you? The manufacturers typically include a zoom with the camera you buy. Zoom lenses are more versatile as they allow you to conveniently carry many focal lengths, all in one lens. You may not realize it, but the manufacturers used to ship new cameras with a 50mm lens or “normal” lens. “All” the professionals used prime lenses, not zooms. Zoom lenses of old were not noted for their quality or longevity.
Things have changed some. Zoom lenses, today, are much higher in quality, and the high-end zooms are weather-resistant and durable. But there are still many reasons a good prime should find its way into your camera bag. Let's review a couple of the advantages to using prime lenses.
The most important aspect, to me, is prime lenses tend to be much sharper. It's a noticeable difference, too. Their design is simpler because they only have to perform at a single focal length. They tend to have less distortion and chromatic aberration because of their simpler design. This is more noticeable on today's high definition, digital cameras than it was when we were still using film.
Prime lenses, usually, have wider apertures. You'll find most of the good primes have much wider aperture capability than typical zooms. Yes, you can buy zooms with constant f2.8 or f4 apertures, but have you priced these? They are very expensive, so the majority of new photographers don't own them. My primes can go to f1.8 or f1.4, again, a noticeable difference.
This matters to us people photographers because those wider apertures equate to better bokeh, or blurred backgrounds. The wider the aperture, the narrower the depth of field you can produce. Check your zoom's aperture capabilities; it's probably f3.5-5.6. In other words, the further you zoom, the smaller the aperture. You want wide apertures for blurred backgrounds.
This doesn't mean you should open every prime lens as wide as possible, it just gives you more control over the depth of field you want to use. Your viewer's eyes will, naturally, go to the most in-focus part of your photo, so, when you use your depth of field properly, you can direct their eyes where you want them. If you look closely at the photo of the captain, below, you'll see most of the photo is not rendered sharply – just the important part that holds your interest.
And, of course, wider apertures mean the lens can bring in more light to your sensor. Very important for night shots, like the one below, or when you want to freeze movement with a fast shutter speed. Remember, the difference is logarithmic, with every full f-stop you open the camera, you double the light. So, from f5.6 (typical on lower cost, variable aperture zooms) to f1.4 is 4 stops, but 16 times the amount of light. That's a huge difference.
So, why doesn't everyone pitch their zooms and carry a full camera bag of primes? One word – convenience. With all their faults, zooms are great for times you only want to drag along one lens. I own three zooms for exactly that reason. I'm not telling you that zooms are worthless, just letting you know there are very good reasons – besides gear acquisition syndrome – to own a prime or two.
If you want to begin with an inexpensive one, start with a 50mm, f1.8. The ones that used to come with our new film cameras. This light lens is always in my bag; it was the lens I learned on. Today, they cost about $150; the 50mm, f1.4 is about $425
For my people photography, I have the 85mm and 105mm. Their slightly telephoto qualities make portraits more pleasing to the eye, amongst other advantages that I mentioned a couple of years ago, when we went through lenses (here is the telephoto blog).
Give prime lenses a try, and learn to zoom with your feet. They have some very distinct advantages and will ratchet up the fun meter.