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Apart from focal length, lenses also vary in their maximum aperture. Wide maximum apertures have several advantages: they give a brighter viewfinder image, give extra options for shooting in low light, and allow you to achieve narrower depth of field. On the other hand, they make lenses bigger, heavier and more expensive. f/2.8 is a wide maximum aperture for a zoom lens, especially if it is maintained throughout the zoom range, but some prime lenses go as wide as f/1.4. Lenses with a wide maximum aperture are sometimes called ‘fast’ lenses but this is so fraught with potential confusion that we won’t use the term. Just watch out if you see a lens described this way: it doesn’t necessarily mean – as you might think – that it has a fast focusing action.

Franco, Cuesta del Viento, Argentina (Chiz) A long lens (400m here) allows the photographer to fill the frame – and the subject’s hair gives a clue how windy it is!

The vast majority of lenses sold today are autofocus lenses. Most can also be switched over to focusing manually, and it is occasionally advantageous or even necessary to do so. Lenses with a very wide zoom range are sometimes referred to as superzooms. There’s no clear definition of what constitutes a superzoom. The widest range currently available in a single lens is 18–270mm, or 15x. This is impressive but of course there are drawbacks. Superzooms may deliver decent optical quality in mid-range but are often less impressive at the extremes – and the extremes are the reason for buying a superzoom. A particular problem is distortion (straight lines appear curved). This might appear to be more of a problem for the urban photographer than the outdoor type, but can you honestly say you never photograph anything with straight lines in?