Features

Digital SLRs have become the camera of choice of discerning photographers, whether they're upgrading from a compact or an older film SLR. While they may at first look familiar, especially to existing film SLR owners, there are a number of differences to be aware of, as well as different techniques for getting the most out of them.

If you're switching from a digital compact, the biggest difference will be how you compose your shot. While a handful of digital SLRs can frame a shot using their main colour screen, the vast majority cannot. Instead, you'll need to put your eye right up to the optical viewfinder and look through it. Like film SLRs before them, these optical viewfinders look through the main lens and allow you to check the focus accurately as you compose the shot.

All but the cheapest digital SLRs also offer a depth-of-field preview button, which temporarily closes the lens iris to reveal the range of distances that will be sharp. The smaller iris means the view looks dim for a moment, but it's still a useful facility.

One of the best aspects of a digital SLR is having a physically large sensor. A typical digital SLR sensor can have 10 times the surface area of a compact camera's sensor, even if both cameras have the same number of megapixels. This means the digital SLR's individual pixels are larger and therefore more sensitive to light. So while most compact images start to look noisy at ISO 400 or even 200, a digital SLR should remain usable up to ISO 800 and beyond, so feel free to increase your sensitivity and experiment.

Probably the most important aspect of digital SLRs is their ability to swap lenses. This provides enormous creative flexibility, although beware of dust when changing them.

Another thing to be aware of is that most digital SLR sensors, while larger than compact sensors, are smaller than a frame of 35mm film. The vast majority measure around 24x16mm, compared to the 36x24mm of 35mm film. This means that any lens you attach will in effect reduce the field of view by around one and a half times compared to a 35mm body.

The typical 18-55mm kit lenses supplied with most DSLRs actually deliver an equivalent range to 27-83mm on a 35mm body. If you were to fit an older 50mm 'standard' lens, it would actually work like a 75mm short telephoto lens. If you're into wide-angle photography, you'll therefore need a much shorter focal length lens than you would with a film SLR.

Some brands also have slightly different field-reduction factors. Canon's non-professional digital SLRs in effect multiply all lens focal lengths by 1.6 times, while Olympus and other cameras using the 'Four Thirds' standard multiply them by 2x. Canon's professional digital SLRs have sensors with either 1.3x or 1x factors. The latter include so-called 'full-frame' sensors that match the size of 35mm film and therefore don't affect the lens focal length. These models are very expensive, though. What's more, ultra-short focal length lenses designed for other digital SLRs have solved wide-angle issues for most photographers.