Lenses

The most popular telephoto lenses cover angles of view from between about 34 degrees (70mm in 35mm format) to eight degrees (around 300mm). Interestingly, the longer lenses have special characteristics that set them apart from shorter teles and require more skill and technical knowledge to be used optimally. In this feature we’ll concentrate on lenses with focal lengths greater than 200mm.

Most kit lenses are very versatile. At the wide end they’re useful for capturing landscapes, while at the tele position, they become handy portrait lenses. In between, you can use them for group portraits, street photography, tabletop shots and even some close-ups. This article shows you how to make the most of your standard zoom lens.

The lens in a camera is like an eye that lets light into the camera body and focuses it on the sensor, where the image is recorded. The larger the optical components (known as ‘elements’) in the lens, the more light gets in. The quality of the elements influences the camera’s picture quality.

We hear a lot about lens sharpness; but what does it actually mean? It’s not easy to quantify but for images to appear sharp, both sharpness and contrast are involved. However, you can’t measure either factor objectively and both are inter-related.

We’ll start by clarifying the definition of ‘macro’. True macro refers only to ‘life-size’ reproduction – which means a 1:1 reproduction (magnification) ratio. In other words, an object that is 20mm high (or wide) will be reproduced at the same size (20mm) on the image sensor.

There are two ways for cameras to measure the distance to an object: they can fire a beam of infrared light at it and measure the time it takes to return, or they can look at contrast differences in a small area of the object and adjust the lens until you maximise the difference. The former system was common in early compact digital cameras and may still be found in many camera-phones. The latter has always been popular in DSLRs and is becoming increasingly common in digicams, particularly the more advanced models. Many modern cameras combine both systems.