• Primes, monofocals and fixed focal lengths - why you should consider one

    We’re all pretty used to zoom lenses these days - you get them on just about everything. Most compact cameras have zoom lenses (some with pretty huge ranges) and most DSLRs come bundled with a zoom lens as part of the kit.

    Zooms are flexible. They’re compact. They’re useful. They’re practical.

    So why would you want a lens that doesn’t zoom? ‘Cos that’s what a prime lens is - one with a fixed focal length that doesn’t zoom in or out.

    Well there are several reasons and perhaps the most important one, at least to start off with, is that they’re cheap. Canon’s 50mm f/1.8 mark II is about £80 and for an SLR lens, that’s very cheap. Of course, they do get expensive too - Canon’s 600mm f/4 L is over £11,000. But for most people, prime lenses are very cheap for what you get.

    Secondly, they’re sharp. Really sharp.

    There are lots of boring technical reasons for this but it’s pretty simple really. When you make a lens, you make it as good as you can. An 18mm lens is made to be as sharp as it can be. A 55mm lens would be too.

    But a lens that changes it’s focal length can’t be optimised throughout the whole range because what’s good at 18mm isn’t necessarily good at 55mm. So manufacturers have to compromise and make zoom lenses perform quite well across the whole range of the lens. The more zooming your lens can do, the more compromised it is.

    Having a lens that doesn’t zoom means you can optimise it completely. You don’t have to fiddle about with fancy glass and moving bits either. It’s just made to be as good as it can be at that focal length. So it’s sharper. It renders colours better. It gives better contrast. You get less colour fringing. And it’s faster…

    Yeah… thirdly, prime lenses are fast.

    In terms of aperture, having a fixed focal length is a real bonus for lens makers. Maintaining a constant widest aperture across a variable focal length range is tricky. Which is why most lenses that cost less than several hundred quid don’t do it - they’re all f/ something to f/ something else.

    There are a few advantages to a fast lens. First is that speed - you can shoot in lower light without using flash or bumping up the ISO.

    That wider aperture, usually f/1.8 or wider, also means shallow depth of field. There isn’t a better way of isolating a subject from it’s background that shallow depth of field. If you’ve ever seen photos and wondered how you get the background out of focus that much, look no further.

    Finally though, perhaps the most compelling reason to buy a prime lens is that it’ll really help your photography. Zoom lenses can lead to “lazy photographer” syndrome. You look through your camera and it doesn’t look quite right so you twiddle the zoom a bit and just take a picture.

    Having to use your feet to move around and recompose a shot makes you take longer and so you think longer. You think more about the overall picture, the final composition, the balance of colour and shape. You think more about how you move around your subject and how you position it. You do all this just because you’re not being lazy.

    And that’s what turns an average picture into a great picture…


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