Lab

Digital Cameras

If you don't already own a digital camera, you don't know what you're missing. With a digital, there's no need to cross your fingers and hope your pictures come out when they're processed - you can check them straight away! Did you blink? Then delete the shot and take another one. And because taking shots doesn't mean using up film, you can be more adventurous - if you're unsure about what exposure to use, you can try a few options and pick the best, safe in the knowledge that you haven't wasted a penny. Better still, the ability to share shots on the spot with friends and family puts the fun back into photography.

Of course, if you already have a digital camera, you know all this. But even if you do, there are reasons to upgrade. The image quality you get from digital cameras these days is breathtaking. A camera with a 3-megapixel light sensor - now pretty much the standard - is a serious rival for the quality produced by 35mm negative film. What's more, the advanced exposure systems in digital cameras will give you a far higher hit rate of successful shots.

Digital cameras aren't just better than ever, they're cheaper too. Whether you're upgrading from an early 1- or 2-megapixel camera, or choosing your first digital model, there's never been a smarter time to buy.

How Digital Cameras Work

Digital cameras may be surrounded by a lot of alien-sounding jargon, but there's really nothing to be afraid of. They're remarkably similar to traditional film cameras. In both cases, a lens is used to focus an image of the scene in front of the camera on a light-sensitive medium. With film cameras it's, well... film. In a digital camera, it's a light-sensitive chip.

The light sensors come in two forms: CMOS chips and CCDs. CMOS chips are used largely in low-cost, low-quality webcams and still cameras at the very cheapest end of the market and in some very expensive digital SLRs. The advantage that CMOS chips bring to high-end cameras is that they consume much less power than CCDs, so batteries last longer. Unfortunately, CMOS chips good enough to use in a decent digital camera are very expensive to make, so most models still have CCDs.

The amount of light falling on the CCD is regulated by the lens aperture - the hole through which the light passes. In cheaper models, this hole has a fixed diameter. In pricier models, the hole is made bigger or smaller by a diaphragm composed of interlocking 'leaves'. This not only alters the amount of light hitting the sensor in a given time, it also has an effect on depth of field -- the smaller the aperture, the greater the range of objects, from near to far, that will appear in focus. The other factor affecting exposure is the length of time that the aperture remains open. This is controlled by a door that opens and closes, known as the shutter. The longer the shutter stays open, the slower the 'shutter speed', and the more light that is let through. Getting the right exposure relies on a combination of aperture and shutter speed. Film and digital cameras are identical in this respect.

The real difference lies in what happens once the image has been formed by the lens and exposed on to the light sensor. With digital cameras, an internal processor collects the digital image data from the CCD and processes the brightness and colour information to produce a digital image, which is saved on the camera's memory card as an image file.

At this digital processing stage, the camera can adjust the colour balance of the image - the 'white balance' - by analysing the colours in the shot. It can also enhance the sharpness of the fine detail.

The number of individual sensors, or 'pixels' that make up a CCD determines the level of detail that it can record. Modern digital cameras have resolutions of 2, 3, 4 or 5 megapixels (millions of pixels). The more pixels the CCD has, the more visual information it can record about a scene. This enables you to enlarge images to a greater extent. Any camera with 3 megapixels or above should, theoretically, be able to produce good, detailed A4-size prints.

Like film cameras, digital cameras let you modify exposure settings using EV (Exposure Value) compensation. This enables you to fine-tune exposures if the camera's automatic settings don't quite give you the result you were looking for. Many allow you to choose which parts of the frame the camera uses to take an exposure reading, offering 'multi-pattern', 'centre-weighted' or 'spot' metering modes. You can often control the shutter speed and/or aperture yourself, either in manual mode or with an automatic mode that gives priority either to the shutter or to the aperture - you choose and take charge of the setting that has priority, and the camera automatically deals with the other setting.

Pictures are stored on removable memory cards, which come in different formats and capacities. Compact Flash is the oldest and cheapest variety. SmartMedia cards are thinner, but have almost died out now. SD (Secure Digital) memory cards are popular, though a little more expensive than other types. The brand new xD Picture Card format used by Olympus and FujiFilm is interesting. Tiny, and with low power consumption. they're available in high capacities - cards now go up to 512MB - and they're not particularly expensive. The only other memory card format of note is Sony's proprietary Memory Stick format, but it's expensive, and you seldom see it outside Sony products.

You get the digital images from the camera to your PC either by removing the memory card and inserting it into an inexpensive card reader connected to your computer, or by connecting the camera itself via a USB cable.