Digital cameras have revitalised photography as a hobby. This year, over 4 million people are expected to make the switch to digital, and with good reason--digital cameras offer a host of advantages over film.

Advantages Because digital cameras record images on reusable memory cards instead of film, there are no developing costs, so you can take as many pictures as you want and only print the ones you like. Most digital cameras feature an LCD viewscreen that lets you perfectly compose your photo and then check to make sure it came out the way you'd hoped. Because the images are stored as standard digital files, your computer becomes your darkroom, letting you crop, enlarge, and retouch your photos to perfection. To share your photos, you have numerous options. You can e-mail them to friends or post them on a photo-sharing Web site. If you want prints, you can use an online photofinisher or create them at home on a photo printer.

Identifying your needs When shopping for a digital camera, start by identifying your needs. Will you primarily be viewing your pictures on a computer screen or do you plan to make a lot of prints? Will you be using the camera for professional graphics work? Will you want a zoom lens? Are there specific features you require, like macro ability or movie mode? Knowing what kind of photos you'll be taking most often will help you decide what resolution, storage type, power source, and other amenities you'll need. Check out the specific features below for more details.

Resolution

Maximum resolution is one of the most important ratings of a digital camera. Digital images are made up of dots called pixels. Resolution refers to how many pixels make up a photo, and it is usually measured in the horizontal by vertical resolution, as in "1,280 x 960," or as a total, like "1.2 megapixels" (meaning 1.2 million pixels). The higher the resolution, the sharper the picture. Traditional film has a higher resolution than digital cameras can muster--at least for now. But today's digital cameras are getting closer and closer to the extreme clarity of film.

Today's consumer digital cameras range in resolution from 640 x 480 (0.3 megapixels) to 2,048 x 1,536 (3.3 megapixels). Common digital-camera resolutions include 2,048 x 1,536 (3 megapixels), 1,600 x 1,200 (2 megapixels), 1,280 x 960 (1.3 megapixels), 1,024 x 768, and 640 x 480. The resolution you need depends on what you plan to do with your photos. If you just want to e-mail photos to your friends or put them on the Web, you'll be happy with a lower resolution like 640 x 480. If you want to print your photos, however, plan on having at least 150 pixels per printed inch. If you try to print lower-resolution images at larger sizes, the results tend to look grainy, blurry, or blocky. Megapixel cameras often offer the option of taking lower-resolution photos so that you can fit more photos in the camera's memory.

Compression

Another factor that affects image quality is compression, the process that shrinks a photo's file size. Most cameras take photos as compressed JPEG files, which allows you to store more images on a memory card. Compression also makes it faster to save and download photos and easier to e-mail photos or download them as part of a Web site. For most uses--e-mailing photos to friends, printing out photos for albums, or posting images on the Web--compressed images are adequate. Compression causes a small amount of data loss, however; if you need the absolute best-quality images, consider buying a camera that takes uncompressed photos. You'll only be able to fit a few uncompressed images on a memory card, but you'll get the sharpest, clearest, most-detailed pictures possible.

Memory and Image Capacity

Memory, the equivalent of film in a conventional camera, is where pictures are stored as you take them. A camera's memory size will determine how many images you can store. If you anticipate downloading your images often, a camera with a large amount of memory isn't as important. But if you plan on taking many pictures without having access to your computer for downloading, you should buy a camera with a lot of included or expandable memory--or plan to buy an extra memory card.

Cameras with internal memory store their images in a nonremovable memory chip embedded within the camera. However, most consumer cameras use external memory--a memory card (CompactFlash, SmartMedia, and Memory Stick are all common types) or even a floppy disk--that you can remove when it's full. You can increase the number of photos you can take by buying additional external memory. Most digital cameras come with enough memory to take from 12 to 36 shots at full resolution--about the same as one roll of film for a traditional camera.

Power Source

Digital cameras use significantly more power than traditional cameras. While typical cameras usually need their batteries replaced every 15 rolls of film or so, you might find your digital camera running out of batteries before you've filled its memory, especially if you use the LCD all the time. Digital cameras use either a rechargeable battery pack or traditional batteries; some come with an AC adapter as well. Consider buying an extra battery pack or investing in rechargeable AAs, and always have extras on hand. Battery life has improved since the early days of digital photography, but limited battery life is still one of the biggest problems with digital cameras.

LCD Viewfinders

Most digital cameras come with at least an optical viewfinder--the kind you look through on traditional film cameras--but many digital cameras also come with an LCD screen built into the back, which you can use as a viewfinder as well. The LCD screen is especially useful because you can see what your picture will look like before you take it. It also allows you to look at the photos you've already taken. As mentioned above, using the LCD screen is a significant battery drain, so if you use it often, have extra batteries on hand.

Lens

The length of a camera's lens determines how much of a scene will fit in a picture. Lens lengths vary between wide-angle (used for landscapes and shots in which you want to include as much as possible) and telephoto (used for close-ups and to zoom in on faraway objects). "Normal" lenses, about 50 mm on traditional cameras, most closely approximate what your eye sees; anything shorter than 50 mm is considered wide-angle, while anything longer is usually considered telephoto.

The image sensor in digital cameras is smaller than the surface of a 35 mm negative, so lenses on digital cameras tend to be much shorter than on traditional cameras. Look for the "35 mm equivalent" rating to get a better idea of your camera's range. Most fixed-length lenses on digital cameras fall somewhere between wide-angle and normal focal length. Many digital cameras now offer zoom lenses, which take you from wide-angle to telephoto. In addition to this optical zoom capability, some cameras provide digital zoom, which is nothing more than software in the camera that crops the edges off of your image and blows up the remaining information to the size of the original. While digital zoom adds extra close-up power, this comes at the expense of resolution. Some cameras also have macro capability, which lets you focus very close and take pictures of small objects--useful for taking photos of flowers, jewellery, etc.

Focus and Exposure

Fixed-focus digital cameras have a non-moving lens that is preset to focus at a certain range. Higher-end digital cameras usually have autofocus instead, which automatically focuses the camera at your subject's distance.

Most cameras automatically determine the correct exposure for the lighting conditions. Sometimes, however, the scene will appear too dark or too washed-out. In these cases, it's handy to have a digital camera that offers manual exposure compensation, allowing you to set the exposure a few stops brighter or darker. A digital camera's ISO-equivalent rating lets you know how light sensitive it is; a camera rated ISO 100, for example, has about the same light sensitivity as a traditional film camera loaded with ISO 100 film. Higher ISO ratings mean the camera is more sensitive to light and can take pictures in darker settings.

Digital cameras work just like traditional cameras when it comes to aperture: the maximum aperture rating of a camera lets you know how much light it can let in. Aperture ratings represent ratios; the lower the aperture rating, the more light sensitive the camera is and the better it can take photos in low light.

Flash

Most digital cameras come with a built-in flash. Basic flash modes should include automatic (senses when to use the flash according to lighting conditions), on (for all photos), and off. Some cameras include additional features, such as red-eye reduction or night portrait mode. Red-eye reduction is ideal for photographing people or animals--it fires a series of short flashes before the final flash and exposure, making your subjects' pupils contract and preventing them from having glowing red eyes in the final photo. Night portrait mode sets your flash to go off at the beginning or end of a long exposure, letting you take portraits set against a night scene, such as a cityscape. However, you should find something steady to set the camera on; the long exposure needed for low light will turn any shake of the camera into a blurry spot in your image.

Display and Image Erase

If your digital camera has an LCD screen on the back, you'll be able to view images stored in memory. Some cameras even let you display pictures on the LCD screen in thumbnail format, usually 9 or 12 to a screen. Most cameras also let you select pictures to erase; this handy feature gives you the chance to edit out the photos you don't want in order to free up memory.

Self-timer

A self-timer sets your digital camera for a delayed exposure, usually giving you about 10 seconds before it takes the picture. This feature is useful for getting yourself in the photo and can also be used to take low-light photos, preventing the camera shake caused by pushing the exposure button.

Audio Recording

A few digital cameras have the ability to record a few seconds of audio with each shot, letting you add a personal sound bite to your photos. This feature tends to eat up battery power rather quickly, so if you use it often, be prepared with extra batteries.

Movie Mode

Many digital cameras now include movie mode, a feature that lets you take short film clips with your camera. To keep from instantly filling your memory card and overwhelming the camera's processor, the movie's resolution is usually much lower than the camera's maximum resolution, and the total length is typically limited to 10 to 90 seconds. It won't replace your camcorder, but it's a fun additional feature.

Construction

The first digital cameras were heavy, clunky boxes that could hardly be called stylish. But today's digital cameras are on a par with the sleek, lightweight form of traditional point-and-shoots, and many feature stainless-steel casings for added durability.

TV Connections

Some digital cameras include a video-out function that gives you the option to hook them up to a TV to display your pictures. With this feature, you can also record your pictures onto a VHS tape.

Computer Connections

Most high-end cameras have software and connections for both Mac and PC computers, but make sure the digital camera you want is compatible with your platform before you buy it. All consumer digital cameras come with the software you need to download your pictures onto a computer. Most also include image-editing software--which lets you crop, adjust, or add special effects to your photos--and the cables and/or cards you need to connect to your computer. Connecting and downloading pictures from a digital camera is easier than you might think; the software and cables are straightforward to install and use. The software supplied is not always the best you can get, so you may want to consider investing in a separate image editing application.

Digital cameras can use a variety of different interfaces. Most use a serial or USB interface, which plugs into a port on the back of your computer. Others come with a PCMCIA interface, which can be inserted directly into a notebook computer. Certain cameras use 3.5-inch floppy disks as memory or provide a floppy-drive adapter for the memory cards.