Once you've chosen your camera type, here are the features you need to consider when buying a digital camera.

Megapixels

How many megapixels (MP) do you need? These are the number of pixels (dots), multiplied by a million, that the camera "sees". The bigger the number, the higher the resolution, and the better the image will look when you enlarge it.

• Even a 3MP camera will produce good quality 4x6 inch prints. 
• Enlargements up to 10x15 inches look better with 4 or 5MP. 
• There's virtually no visible difference in a 6x4 inch print between a 6MP and 10MP camera. Resolution over 5MP only becomes important if you're planning to enlarge your photos to poster-size or crop them hugely. If this is likely, look for a 7MP to 10MP camera. Otherwise, resolution is less important than sensors, lens quality, and other factors that affect photo quality.
   

Guide to the table

Image size: Average size of a jpeg file (best quality) taken at this resolution.
Print size: The print size you can enlarge to without a noticeable loss of quality.

Resolution

Most cameras let you choose between several resolution settings. A low-resolution shot will take less storage space than a high-resolution one - useful if you need lots of quick-reference images, rather than a smaller number of high-quality ones.

Memory

A few cameras have a small amount of built-in memory, but in general you'll store most of your pictures on a removable memory card. A low-capacity card (often 32MB) is usually supplied with the camera, but will only store around 10 or 20 images. 256MB should be enough most of the time, but more could prove valuable if you're away from a computer for long periods and can't download your images - or if you plan to take a lot of photos at high resolution.

There are six main formats: CompactFlash, Secure Digital, xD, MultiMedia, Smart Media, and Memory Stick. Most digital cameras are compatible with only one format, but the brands aren't proprietary. Canon, Fuji and Kodak, for example, all make CompactFlash cards.

Batteries

Some cameras have their own integrated (rechargeable) batteries and include a charger; others accept general-purpose AA batteries. We test battery life using a cycle of actions: turn on, zoom in and out, take photo, view image for five seconds, then delete. The majority manage around 255 cycles before running down - scoring 10 out of 10 in our table of test results. The worst performers were still reasonable, surviving for about 100 cycles.

Zoom

The optical zoom physically moves the lens, giving a closer view with no loss of quality. Don't worry about the digital zoom, which just enlarges the pixels in the image. This will reduce quality and can produce a jagged or pixellated result if you zoom too close.

Digital SLR cameras, like the old film cameras, usually use focal length as a measure of zoom, such as a 28-70mm or 70-300mm zoom lens. Compact digital cameras usually use a zoom ratio such as 2x, 3x, 12x.

Can you compare them? Yes, there's a simple rule. For a dSLR lens you divide the largest focal length by the shortest. So for a Canon 55-200mm lens you would divide 200mm by 55mm to get 3.6x - the zoom ratio of the lens. A 100-400mm lens has a 4x zoom ratio and a 35mm-350mm lens has 10x zoom.

Monitor and viewfinder

• Brightness and contrast can be adjusted on many monitors - a handy feature if you're struggling to see it in bright sunlight, or a dark room.
• The monitor on most dSLRs is for reviewing images only - you can't use it for previewing a shot. This is where a good viewfinder is essential. 
• Some people with a standard digital camera prefer to use the viewfinder instead of the monitor, if they're trying to save battery life (by turning the monitor off), or if the background light is too bright to see the monitor clearly.
• Some viewfinders have a "dioptre adjustment" (eye correction) feature - allowing short-sighted people to view the image without having to wear glasses.

Other features

Manual settings
The more manual setting options you have, the more you can do with the camera. Most will let you control file type, quality, focus, aperture and shutter speed. Look also for meter options: spot metering lets you set the exposure to one part of the image, field metering takes in the whole frame.

There may also be pre-set options for different types of scenes, such as "Beach/Snow" (low exposure), "Landscape" (long focal distance) and "Fireworks" (slow shutter speed).

Shutter delay
Photography is about capturing the moment - and a photo isn't taken the instant you press the button. There's a time delay, known as shutter delay or shutter lag. That time delay can mean the difference between a prize-winning image or a photo destined for deletion.

Many compacts have a shutter delay of half a second or more, and some can take up to 2 seconds. dSLRs typically take photos much faster, because of their optical viewfinder and bigger electronic processor.

Macro
A macro setting allows you to take extreme close-ups. Most cameras have this, but the minimum focal distance differs, from about 1 to 20cm. Even without a macro setting, many cameras will be able to focus on objects quite close to the lens. Less than 10cm is good.

Movie function
Most compact cameras allow you to take short video clips with sound. Some models allow up to an hour of footage if you have a large memory card. The movie quality between digital cameras can range from very poor to rivalling modern digital camcorders. If this is important, check out our test scores for movie quality.

Flash
Red-eye reduction is present on almost all models. A few have an extra "hot shoe" or similar connection which allows you to attach an external (and more powerful) flash.

Portability
Look for a camera that is not too heavy and has a sturdy design. Fold-out screens can be flimsy, but also very useful. Cases/bags are not usually supplied, but can be bought separately.

Output options
Many models hook up to a television so you can view your photos or short films on the big screen. You may be able to play sound as well.

Tripod attachment
Always a useful feature if you're interested in anything more than casual snaps.

Image-editing software
Basic programs are sometimes supplied, although you may want to buy your own. Image editing is a lot of fun, and the only limit is your imagination. See our test of photo-editing software to pick a good one.