Over at DPReview.com, in the Sony DSLR/DSLT forum, a self-proclaimed “newbie” asked a very reasonable and practical question. He wanted to know if he’d see a visible improvement in his photos if he were to buy some prime lenses and use them. (In case the term is unfamiliar, a “prime” lens is one with a fixed focal length, in other words, one that is not a zoom.)
It’s common for enthusiasts to insist that primes make a big difference to image quality. I disagree, at least with the adjective “big”.
If you buy primes, do not expect to be wowed by the results you get. You almost certainly won’t be. When zoom lens were still new-fangled (that is, about forty years ago), most of them weren’t optically very good. Nowadays, the best zooms rival excellent primes in image quality. If the only zoom lens you’ve ever used is the 18-55 f/3.5-5.6 kit lens you purchased with your camera, well, you might perceive some improvements with a good prime, if you really look closely. Then again, you might not, especially at first. A prime lens isn’t a magic pill.
So, keeping in mind how limiting prime lenses are, if primes don’t automatically make strikingly better photos, why do people buy them? Why do I buy and use prime lenses? There are a number of reasons. Here are half a dozen.
1. Wider maximum aperture
If you want something wider than f2.8, you pretty much have to get a prime. There are some top-of-the line compact cameras with zoom lenses that go wider than f/2.8 at the wide end (like my Sony RX100) but the big lenses for DSLR/DSLT bodies don’t. Want f/2 or f1.4? You’re getting a prime.
Does this make the images “better”? Well, in one sense, you can’t possibly compare, because a zoom can’t shoot at that aperture. Fairer to say that it makes that picture possible. At f/5.6, I’d be hard pressed to tell whether a given photo was taken with a prime or a good zoom.
2. Shallower depth of field
Wider apertures of course allow you to get shallower depth of field. Want to blur the background? Open the aperture as wide as possible. And “as wide as possible” pretty much means “on a prime.” See previous item.
3. Small is beautiful
Primes tend to be smaller and lighter than good zooms. The Sony DT 16-50 f2.8 is six times bigger and weighs about twenty times more than the Sony 50 f/1.4. I exaggerate, of course, but only slightly.
4. Mechanical reliability
Primes are mechanically more reliable than zooms, I guess because they’re not as complicated mechanically. I confess I’m a bit tentative about this reason. May have been truer in the past than now.
5. Optical reliability
The reliability of prime lenses extends also to image quality. There are lots of technical factors in excellent optics: distortion and aberration, vignetting, sharpness, color rendition, bokeh. It’s easier to get these things right for one focal length than to get them all equally right for a range of focal lengths in a single lens. That’s why most zooms have a sweet spot, somewhere around f/5.6 and the middle of the zoom range where they perform bests in all respects.
Still, the difference here is not so dramatic as it used to be, and it must be acknowledged that there are inexpensive primes that really don’t match the excellence of certain high-quality (and expensive) zooms. And on the other hand, it should also be noted that you don’t have to pay and arm and a leg for a good prime lens. Sony sells a series of really good prime lenses each of which sells for just a few hundred dollars. They saved money by making the barrel of the lens out of plastic, so they not only are cheap, they feel cheap, compared to some of the old-time metal lenses. But there’s really nothing wrong with plastic nowadays. The lenses seem quite sturdy and they’re much lighter than older metal ones.
6. Prime lenses alter the way you see, or, It’s a Zen thing
Really this ought to be reason #1, but I’ve saved it for last partly because, of all the advantages of primes, this is the most important, and partly because it’s also the most difficult to articulate.
Knowing you’ve got one focal length to work with forces you to think differently about your shots, to become more deliberate. If you’ve always shot with zooms, working with a single focal length is awkward and uncomfortable at first. But if you stick with it, it becomes easier; and then it starts to make sense. Work with two or three primes for a while and you start seeing the world differently, because you can actually see those couple or few angles of view. If you shoot with a zoom, well, anything is possible — not just possible it’s easy — and that infinitude of possibilities is ironically rather discouraging. True, shooting with a prime, you may have to move your body to achieve the composition you want (also knowing as “zooming with your feet”) but in return you won’t be fussing with the lens’s zoom mechanism.
It’s a zen thing: by limiting yourself to a single focal length, you achieve another kind of freedom, a disciplined, artistic freedom that some photographers, at least (including yours truly) find inspiring and exciting.