A digital camera has some big advantages over its film-using counterpart. Photographs are available for use as soon as they're taken, and they can be transferred to a PC in a matter of seconds, with no loss of quality.

Like a regular 35mm camera, a digital camera takes still photographs but rather than store them on film, they're stored electronically as an image file. The obvious advantage of this is that an image file can be read by a computer straight away, bypassing the need for developing and scanning.

It all boils down to a light-sensitive component called a CCD (charge coupled device) and some kind of storage device, usually a solid-state memory card. Once you have an image that's been captured digitally, it can be manipulated in any way you choose using a computer and some image-editing software.

This can be as simple as resizing and cropping for printing, correcting the exposure, removing scary red-eye or performing some Stalinesque non-person removal. The neat thing is that because it's all done digitally, no-one will be able to tell.

At your convenience

Convenience is the key here. With a good-quality camera and a decent colour printer, you can be printing out perfect A4 enlargements or emailing your snaps around the world just minutes after you've pressed the shutter.

Pound for pound, the image quality of a digital camera is also far lower than that of a film camera, since the CCD of even the most expensive model can't match the resolution of a simple strip of film. Since less detail is captured, try blowing up a digitally-acquired image to a size greater than about 6x4in and you'll soon start noticing a degradation in image quality.

Lens me your ears

Digital-camera manufacturers have also tended to shy away from investment in quality lenses and this does little to help image quality either. This situation is changing, though. Nikon's digital cameras use Nikkor lenses like those used for its SLR range, and other manufacturers are being forced to make changes thanks to high-quality CCDs that aren't so tolerant of poor optics.

Convenience? Rapid access to photographs is all very well, but unless you have equally easy access to a PC, they'll be staying in the camera until you get home. It's possible to carry a handful of memory cards around of course, but these are rather costly.

Why do you want a digital camera?

If you've identified a serious business need that a digital camera will immediately address, then fine. Many estate agents are using digital cameras to take photographs of properties for DTP documents printed out for buyers - an application that saves both time and money.

If you want to try your hand at digital imaging at home, then think seriously about investing in a decent colour flatbed scanner instead. If you have a good 35mm camera, you will be able to digitally manipulate images on your PC for a fraction of the cost of a digital camera.

If you're sick to death of having to fire off a film before waiting a whole hour for your snaps, then a digital camera is obviously the answer to your prayers; but don't be fooled into thinking that you can chuck your old camera. Using a digital camera effectively needs some discipline - the photographs you plan to keep need to be stored and indexed on a PC using some suitable software.

What to look for

Buying a digital camera is much like buying a 35mm one and a lot of the features to look out for are common to both. When looking at a digital camera, pick it up and hold it. Not all digital cameras are that comfortable to hold, and unless you're happy with the way yours looks and feels, you won't be inclined to use it in public.

• Viewfinder

Next, try framing a shot. If the camera has an optical viewfinder, great. If it doesn't, bear in mind that while LCD viewfinders are fine for framing shots and great for viewing them afterwards, they're useless in bright sunlight and can soon drain a set of batteries.

• Lens

Unless you're working to a tight budget, your next priority should be a zoom lens. Just as with 35mm compacts, the standard lens on a digital camera generally has around a 38mm equivalent focal length. This makes it very difficult to fill the frame with your subject and show any real detail, and a zoom means you can get in much closer.

But beware of so-called digital zooms: all they do is crop the picture and blow up the remainder. You'll get the same results by taking your pictures at high resolution and cropping them manually.

• Flash

While digital cameras are great at taking pictures in low light conditions (their CCDs are surprisingly sensitive and you can always adjust light levels on your PC), a flash is essential. All of the models reviewed here come with one, but it's worth checking to see how many modes are offered.

It should have a red-eye mode and you should be able to turn off or use it for fill-in work. On some cameras, notably Ricoh's, the flash is set to off when you turn the camera on. Although this saves batteries - the flash doesn't have to charge up except when you need it - it can be annoying if you have to wade through menus to turn it on again.

• Autofocus

Decent autofocus is vital too. Just as on a compact camera, a fixed focus lens risks blurring some subjects and losing detail. Since no film is involved, a dealer should be happy to let you take a few snaps with a digital camera - try a few with near and distant subjects to assess the autofocus. Some models have slower mechanisms than others.

• Storage

Digital cameras mostly use solid-state memory cards for storing images. While there's little to choose between the SmartMedia and Compact Flash memory cards, Compact Flash cards appear more robust.

On the other hand, only SmartMedia cards can be used in floppy-disk adaptors like Fuji's FlashPath device. If you want to add more, both cards are depressingly expensive - around £50 for an 8Mb card.

• Image transfer

If a digital camera uses solid-state storage, it will also come with a cable to link to your PC for transferring images. This is a simple way of doing things, but the speed of a serial cable means it's not particularly quick to transfer several images, though Kodak also provides USB and infra-red connectivity on its top-line cameras.

A more convenient option is to use a memory card reader. If you've got a notebook PC, then you can use a Type II PC Card adaptor to read CompactFlash cards, and many cameras come with one as standard.

Parallel and USB port readers are also available for desktop PCs, and FlashPath devices provide a handy way to read SmartMedia cards in a floppy disk drive. The software supplied with a camera also makes a huge difference.

Drawbacks

As long as you buy a megapixel model (one with at least a million pixels, though the DC200+'s 1152x864 resolution is close enough), you'll be able to print decent images at up to around 7x5in. Lower resolutions than this are best saved for on-screen use.

As it takes time for the image to be registered by the CCD, processed and transferred to the memory card, it's rare for a digital camera to be any good for rapid-fire picture sequences.

Action pictures can be difficult too - there's always a delay between pressing the shutter and actually taking the picture. Small children move quickly enough for this to be an insurmountable difficulty for family snaps.

The biggest problem with digital cameras, however, is battery life. Displaying pictures on a colour LCD takes a lot of juice, as does writing them to a memory card.

Extra features

As you'd expect, the more you pay for a camera, the more facilities it has, though there are certain poor-value exceptions.

Setting the camera to take black-and-white or sepia-tinted snaps is fun but still a gimmick. You gain more flexibility and better results by taking standard shots and manipulating them on your PC.

If you want to stitch together pictures to make a panorama, then packages like Spin Panorama certainly help, while Canon and Casio cameras can show an overlay of your last shot on their display, helping you to match up the edges.

Kodak and Nikon also offer connectors for an external flash on their most expensive models.

What else do I need to buy?

While it's possible to use a digital camera on its own, viewing snaps on a TV with the camera's video output, it's hardly ideal. But unless you have a PC, you cut down your options for editing and printing photos, while your only option for long-term storage is to buy more expensive memory cards.

Even the cheapest PC should be quite adequate for simple picture storage and will cope happily with printing. If you want to really build up your image-editing skills, though, a more expensive machine and better software will pay dividends.

Every camera is supplied with a basic image-editing package (Photoshop LE is supplied with the Nikon) and the likes of Picture It or PhotoDeluxe are fine to get you started. A professional image editor like Adobe Photoshop probably isn't worthwhile unless you want to apply lots of sophisticated effects, but upgrading to the full editions of the packages supplied does allow you to use more features.

Finally, you'll need a printer. Dedicated photo printers offer great quality but are expensive to run and only offer images up to 6x4in.