Lab

Budget Digital Cameras

It's only a few years since digital cameras first appeared. Those early models were fun - they let you take a peek at your snaps immediately, or e-mail them to friends - but unless you paid through the nose, pictures could look more like stills from dodgy CCTV footage. And they were certainly more expensive than comparable film cameras.

How things have changed. Now you can get a very decent digital snapper for less than 150 quid. The only catch is that you have to know what you're buying. The specs on the box may shout about "megapixels" and "digital zoom", but these won't help you separate the bargains from the bum deals. You need to handle a potential purchase, check out its controls, see what the pictures look like or, alternatively, you need to get someone you trust to do it for you. That's where Computer Buyer comes in. We've tested six of the best budget digital cameras to find out which one really is a spanking good bargain.

How do digital cameras work?

Digital cameras are actually a lot like their conventional counterparts: images are recorded by exposing a light-sensitive surface. In the case of old-fashioned cameras, this is film. In the case of a digital camera, it's a light sensor called a CCD (short for 'charge-coupled device'). This chip contains millions of tiny light-sensitive cells, which build up electrical charge while they're exposed to light.

How much light the photo-sensitive cells can collect depends on two things:the size of the hole through which light is let in, called the aperture, and the length of time it's left open. This is controlled by the shutter speed. The fact that light is collected over a period of time explains why digital photos come out blurred when you move the camera while taking a shot. Getting the correct exposure depends on the camera picking the right combination of aperture and shutter speed. Some cheaper models, however, have a fixed aperture, and rely on shutter speed alone to control the amount of light falling on the CCD.

The grid of tiny, light-sensitive cells on the CCD's surface record the intensity of the light collected, along with other information such as colour saturation. This signal is then turned into digital data by the camera's analogue-to-digital convertor (ADC), and stored in the camera's memory chip.

Some cameras use a type of sensor called a CMOS chip, rather than a CCD, but the basic principle is the same.

Conventional cameras allow you to use films with different ISO ratings depending on the light levels in your environment. Digital cameras do something similar by amplifying the signal from the CCD, so that it appears to have recorded more light than it actually has. The problem with this, though, is that it magnifies any discrepancies too, which can show up as random coloured speckles, especially in darker areas of the picture. This is known as digital 'noise'.

The number of tiny cells in the CCD doesn't translate directly into the number of dots or 'pixels' in the image. Some cells are reserved for calibration purposes, and others may simply not be used by a particular model of camera. What counts is the number of 'effective pixels'. This dictates the maximum image size that can be captured. For example, a 3.2-megapixel camera can capture images measuring 2048x1536 pixels. Ignore any higher 'interpolated' resolutions, as these create more pixels by taking an educated guess at what they would contain - they don't actually add any extra detail. Interpolation provides similar results to scaling up images in your photo-editing software. Watch out for claims such as 'up to 3.0 megapixels'. This usually means that the camera doesn't really have a 3-megapixel CCD.

Image files are usually compressed by the camera's electronics so that you can fit a reasonable number into memory. Without compression, a single 3-megapixel image would fill a 16MB memory card. Most budget digital cameras save images as compressed files called JPEGs, letting you save 20 or more.

Most cameras have a USB port so that you can plug them straight into a PC. A software utility is usually provided to help you select pictures from the camera to transfer to your PC. In Windows XP the camera should also appear in My Computer as a removable drive, allowing you to move pictures in and out of it as if it was another hard disk. This is very convenient, but with some models you need to be sure you use the Safely Remove option that appears in the Task Bar's notification area before unplugging the camera, to avoid problems.

What to look for

The quality of a camera's construction is important, as you'll be carrying it around a lot. It's also vital that you can grip it comfortably and operate the shutter button (the one you press to take a picture) and zoom control without having to look for them. The LCD screen on which you compose your shots needs to be clear and bright, and buttons and menus should be easy to understand.

As with a film camera, the quality of the lens (in reality an array of lenses) is crucial. A zoom lens is useful not only for capturing distant subjects, but also for varying composition and depth of field. Not so useful is 'digital zoom'. This has nothing to do with optics, but just scales up part of the image captured by the CCD, giving a progressively larger but lower-quality picture of the subject - you don't get any extra detail. At the other end of the scale, a 'macro' mode (an optical feature) should enable tight close-ups of small objects.

All these moving parts, and the LCD, are bad news for battery life. Only one of the cameras on test comes with rechargeable batteries and a charger as standard, while the others (except the Relisys) take ordinary AAs, but have optional charger kits. A charger and two sets of batteries - so that you can use one and carry a spare - is the best option, but can add quite a bit to the cost.

As we've said, the cameras use JPEG compression to reduce the file sizes of images. If too much is used, it can spoil the clarity of your pictures. Look for a quality setting that can reduce the amount of compression used, at the expense of storing fewer pics in the camera's memory. All the cameras on test come with a meagre 16MB of memory. Happily, though, all have slots for standard types of removable memory cards. These tiny cards are fairly inexpensive these days - a 64MB CompactFlash card costs less than £20 from www.dabs.com.

Another important function of the camera's electronics is 'white balance'; adjusting the appearance of colour and tone in the picture according to the lighting conditions. If this goes awry, indoor shots under electric (tungsten) lighting, for example, will look yellowish. Your camera should be capable of judging white balance correctly most of the time, but it's useful to be able to set it manually - to Sunshine or Fluorescent, for instance - when necessary.

All the cameras can also record short movies, in either AVI or QuickTime format, typically at 320x240 resolution; all but the Olympus can include audio. We didn't take video performance into account in our ratings.