Digital cameras use an image chip to convert light into an electrical signal. This is composed of thousands of light-sensitive cells called pixels - they’re like the dots that make up a newspaper photograph. As a rule of thumb, the more pixels in the chip, the sharper the image. All image chips now have at least a megapixel (a million pixels), and most have two or three megapixels. You can buy a camera with a two-megapixel chip offering photo-quality pictures for less than pound;200. This should be fine for most schools.

The images are usually stored on reusable memory cards. High quality pictures need a lot of storage space. Most digital cameras have cards with four or eight megabytes, although larger sizes are available. Prices vary from pound;10 to several hundred pounds.

If you want to mix and match several digital cameras, bear in mind there are around half a dozen types of memory cards, mostly incompatible with each other. This normally shouldn’t be a problem, as most images are put into a computer, but it may stop you swapping cards between cameras.

Digital cameras today are simple to use, with automatic focus, exposure, colour balance and flash, so even the youngest pupils should have few problems handling them.

Digital cameras are widely available from specialists such as the Digital Camera Company (www.digital-cameras. com), photographic retailers such as Jessop’s (www.jessops.co.uk), computer stores such as PC World (www. pcworld.co.uk) and high street retailers such as Dixons (www.dixons. co.uk). Your local authority supplier or purchasing company may also stock them. Online suppliers are generally cheaper than on the high street.

Add-ons include a rechargeable battery and more memory. For field trips, a waterproof case is very handy.