In the second part of our Shoot Like A Pro Series on how to get the sharpest photos possible with your camera’s lenses, we turn our attention to prime lenses. In this post we explain why you might wish to swap the convenience of a zoom lens for the speed and quality of a prime lens to drastically improve the quality of your photos.
Fixed focal-length lenses (primes) may seem a bit like dinosaurs in these days of image-stabilised zoom lenses and the high-quality ISO capabilities of the latest DSLRs, but they still have a place in your camera bag.
Sharpness is the key reason why prime lenses are such a great choice. With zoom lenses you get the convenience, but this is often at the cost of image quality, with barrel and pin-cushion distortions appearing at the wide-angle and telephoto ends of the zoom range.
You can also expect an increase in colour fringing around high-contrast edges in a scene when you use a zoom, as well as vignetting. This latter effect is most commonly seen when you’re using large apertures at the wide-angle end of your zoom.
What’s more, zoom lenses are also more prone to ghosting and flare.
Switch to a high-quality prime lens, and distortion and vignetting will be much less noticeable. Sharpness should also be excellent, so you can really make the most of the high-resolution sensors fitted to current digital cameras.
There are plenty of prime lenses to choose from. The prices of extremely fast wide-angle and telephoto optics are verging on lottery-win territory, but there are more reasonable options around such as the Nikon 50mm f/1.8 that we’ve been using, which is available for under £100.
After sharpness, the main advantage of using a prime lens over the more common zoom is the wider maximum aperture, which enables you to shoot in lower light levels at the same ISO without risking camera shake.
When people say that prime lenses are ‘faster’, what they mean is that prime lenses have a larger maximum aperture, which allows you to shoot at quicker shutter speeds.
A typical 18-55mm zoom lens, for example, has a maximum aperture of roughly f/4 at the wide-angle end, shrinking to a mere f/5.6 at about 50mm. Switch to a 50mm f/1.4 prime lens and the largest available aperture is four stops faster.
In low light you’d be limited to a shutter speed of around 1/15 sec with a typical zoom (unless you increase your ISO setting).
However, an f/1.4 lens will allow you to use a much faster shutter speed of around 1/250 sec. An f/1.8 lens is 3.3 stops faster than an f/5.6 lens, and even an f/2.8 model is two stops faster.
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