Want to shoot a crowd, capture a distant animal, change your perspective or snap the perfect portrait? Add to your lens collection, says Steve Davey
Your lenses are the eyes of your camera: they affect what your camera sees and how it sees it. Yet many photographers stick with the lens that came packaged with their digital SLR (DSLR). There is nothing wrong with the kit lens. It generally covers some of the most useful focal lengths. But these are basically the same as the focal lengths on most compact cameras – so if you only use the kit lens, you are essentially forcing your expensive and sophisticated DSLR to behave like a compact camera and missing out on a whole world of creative possibilities.
The power of a lens is expressed by its focal length, measured in millimetres. For a 35mm film camera, a 50mm lens – termed a standard lens – gives approximately the same perspective and magnification as the human eye. Anything with a lower focal length is progressively more wideangle, while lenses with higher focal lengths are progressively more telephoto. As the focal length doubles, the magnification doubles as well, and vice versa.
As well as magnification, it is worth thinking about field of view. A wideangle lens will encompass a wider field of view than a telephoto lens – in essence, cramming more of the scene in front of you into your picture. A telephoto has a narrow field of view, isolating a smaller part of the scene.
Most consumer-level DSLRs have a crop sensor, smaller than the dimensions of 35mm film – so each resulting picture is cropped smaller. For most DSLRs this size reduction factor is around 1.5x. For the squarer Four Thirds system, the size reduction (crop factor) is 2x.
The effect is that the focal length is effectively magnified by the crop factor, so a 50mm lens on a crop sensor camera would typically have the same magnification and field of view as a 75mm lens on a 35mm film camera. Some expensive professional-level cameras have full-frame sensors that are the same size as 35mm film – on those models, lenses behave the same as they would on a 35mm film camera.
The kit lens packaged with a DSLR is usually a zoom with a range of focal lengths, typically 18-55mm. On a crop sensor DSLR (with a 1.5x crop factor) this is equivalent to a 27-83mm lens on a 35mm camera – at the limits of its range, it will behave like a moderate wideangle through to a weak telephoto. It’s a good general lens, but you’ll miss out on the extremes of a powerful telephoto or super-wideangle.
The effect of a lens is about more than just crop and field of view. Each lens will have different characteristics and give a different look and feel to your pictures.
By cramming a wide field of view into the frame, a wideangle lens distorts the picture in a dynamic way, especially at the corners. It also exaggerates perspective, making subjects appear further apart. Nearby objects appear relatively large, while distant objects and backgrounds will appear much smaller.
A telephoto lens tends to compress perspective, making objects appear closer –perfect for making crowds seem more crowded. Telephoto lenses tend not to distort, giving very flat images. They also give less depth of field than a wideangle, so are ideal for using the technique of blurring the background.
The more powerful the lens, the more pronounced these characteristics and the more extreme the photographic effect – your pictures will look completely different to anything you could observe with the human eye.
By investing in a range of lenses you can produce images in a range of scenarios – architecture, interiors, even wildlife – that would be more difficult with the limited range of focal lengths available with the standard kit lens.
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