Everyone loves taking photos but, if you're not using a digital camera, you're seriously missing out.

Digital cameras let you see your pictures straight away and delete them if they've turned out bad, while most models can record short video clips and produce slide shows of your snaps on your TV. Try doing that with a Polaroid.

Prices have dropped heavily and now a perfectly useable model can be had for around £150. Spend a little more and you get a range of features that will satisfy even demanding photographic enthusiasts.

Digital cameras are flying off the shelves, outstripping the traditional film market by two to one, and with a PC you've got a powerful digital darkroom without any nasty chemicals or fumbling round with the lights off.

But with the vast range of models now on sale, making a decision has never been harder. What is a megapixel and how many do you need? Is there a catch with digital zooms, and will you have enough memory for your holidays?

There are plenty of questions to answer, so allow us to expel the myths, banish the jargon and explain everything you need to know about buying a digital camera.

Quality and megapixels
The single most important thing about any digital camera is the resolution of its image sensor (the part of the camera that captures the image), measured in millions of pixels, or 'megapixels'.

In theory, the more megapixels you have, the greater the detail captured and the better the quality of your pictures.

With today's cameras sporting anything between one and five megapixels, the big question is how many do you actually need? It also doesn't help that some manufacturers count their pixels in different ways.

To answer how many megapixels you need, ask yourself how big you'd like to print your pictures. As you make bigger enlargements, the individual pixels become more obvious until you start seeing undesirable blocky squares and jagged lines.

The more megapixels you have, the bigger the enlargements you'll be able to make while still maintaining a decent quality.

Having more megapixels also allows you to crop an image and still have sufficient detail to make a good print.

When printing with colour inkjets, it's easy to see how far you can push various digital pictures before they begin to lose quality. The following figures are guidelines for true photographic quality on prints held at arm's length.

One megapixel images look fine printed up to 5 x 4in, while a two megapixel picture is good up to 8 x 6in. Increasing to three megapixels allows 10 x 8in prints, while four megapixel cameras can manage prints up to 11 x 9in.

Finally, today's top of the range five megapixel models can stretch to 12 x 10in. For the techies out there, we reckon 200 pixels is required per printed inch.

Of course, you're welcome to print any picture as big as you want, so long as you know it may not look great. Viewing distance has a significant impact and you can get away with bigger enlargements the further away you stand.

It's all a question of personal expectations and a little experimenting to see what sizes are acceptable for your purposes.

We should finally point out that the vast majority of digital cameras take pictures which are the same squarish shape as a normal TV set - these are less wide than those taken by a 35mm camera.

While a one megapixel camera can make postcard-size prints, most people will be much better served by a two or preferably three megapixel model, especially as these also tend to have better lenses and overall features.

Four and five megapixel cameras are, however, only justifiable by those who either want to make bigger prints or own a particular higher-end model they like the look of.

When is a megapixel not a megapixel?
As mentioned earlier, some manufacturers count their total number of pixels in different ways.

Fujifilm describes its two most popular 'SuperCCD' cameras as having 4.3 and six megapixel output when, in terms of actual physical pixels, they actually only have 2.4 and 3.3 megapixel resolutions respectively.

Fujifilm claims that the unique design of the SuperCCD image sensor captures more detail than a normal chip, which therefore justifies enlarging the images within the camera to the described outputs.

The result is contentious. Certainly the final images contain 4.3 or six megapixels but, in terms of actual detail captured in our tests, they're little better than normal 2.4 or 3.3 megapixel cameras respectively.

That's not to say that Fujifilm is playing tricks; it's just important to understand how to compare its SuperCCD cameras with other manufacturers' models.

Interestingly, other manufacturers have jumped on a similar bandwagon and offer internal scaling options within their cameras. These use a technique called interpolation, which simply invents extra pixels and inserts them between real ones.

It can be quite an effective way of eliminating jagged edges on big enlargements but remember, interpolation will never create detail which was not originally captured. It's merely a way of making educated guesses about what to fill the gaps in with.

Consequently, since interpolated pictures take up more of your camera's precious memory space, we'd sooner do it later if necessary, using photo software on the PC.

The bottom line then is once again to ignore scaling and output tricks. Concentrate on the genuine resolution of a camera to get a real measure of how it is likely to perform.

Lenses
The second most important thing about a digital camera is its lens; after all, the most megapixels in the world won't make a good picture if the lens is poor.

There are many different things to look out for, but the most important is the difference between optical and digital zooms.

Optical zooms use the actual lens to adjust the amount of information captured in your picture. Digital zooms merely crop the image and enlarge the central portion, thereby reducing the total number of pixels and overall quality.

Since you're free to crop and enlarge on your PC later, digital zooms are effectively a waste of time and best ignored.

The important figure then is the genuine optical zoom, which typically operates in a 3X range, roughly equivalent to a normal 34-102mm lens on a 35mm camera.

It should be noted, however, that 3X on one digital camera may not be quite the same as 3X on another, as some cameras start off with wider angles and subsequently don't get quite as close at the telephoto end. Compare the equivalent ranges if you're after something specific.

More importantly, some cameras offer more powerful 5X, 8X or even 10X optical zoom lenses. These offer maximum zooms equivalent to a 150-300mm lens on a 35mm camera and are therefore perfect for getting close to distant subjects like wildlife, sports events or celebrities.

What most digital cameras have in common though, are lenses which cannot be removed. Better models offer optional lens attachments which slightly extend or reduce the range, but these can be large and expensive.

Consequently, you should choose a camera with a lens appropriate to the kind of pictures you're going to take now and in the future.

The longer zooms certainly seem tempting but are generally only useful to specialist photographers; most people will be satisfied by 3X or 4X optical zooms.

The actual lens quality is crucial to overall picture quality, with cheaper ones often appearing slightly fuzzy in the corners or suffering from coloured fringes around the edges of objects in front of bright backgrounds.

Lens quality is impossible to measure by comparing numbers or claims in adverts but generally speaking, you really do get what you pay for and longer zooms are usually harder to get right than shorter ones.

One final word for owners of 35mm SLR film cameras who want to go digital but still enjoy the flexibility of removable lenses. Digital SLR cameras are available but are currently very expensive, costing from around £1,500 for the body alone.

Additionally, while digital SLRs can take existing 35mm lenses, their effective focal length is typically multiplied by 1.5 times because the imaging chip is smaller than 35mm film - great news for telephoto fans but terrible if you're into wide angles.

Closer than close
If you're into extreme close-up photography, say of stamps, coins or flowers, then a good macro mode is essential.

All digital cameras offer a macro mode but these vary considerably in how close you can get to your subject. For good macro results, you should choose a camera which can focus much closer than 10cm - ideally 5cm or closer still.

True macro fanatics choose models which can focus as close as 2cm, which allows a pound coin to almost fill the entire picture.

Memory
Digital cameras store their images in computer memory which can be erased and reused. While some budget cameras have built-in memory, most models employ removable memory cards.

Clearly the more memory you have, the more pictures you can store before either having to delete or transfer them onto your PC.

All digital cameras allow you to choose lower resolutions and higher compression in order to squeeze on more pictures, but both will reduce your image quality.

To get the best quality from your camera, use the highest resolution and the least compressed JPEG setting. The problem is that most cameras are only supplied with enough memory to store between 10 and 20 shots at the best settings.

The answer is, of course, to buy a new memory card and we believe that every digital camera owner should budget for one straight away.

Memory cards come in different formats, so make sure you're buying the right one for your camera. Alternatively, you may want to choose a camera based on support for the cheapest memory cards.

Compact Flash and SmartMedia are currently the cheapest cards, but the latter is gradually being phased out. Newer SD/MMC and XD cards look like being around for a while but are currently the most expensive.

In the middle, you'll find Sony's Memory Sticks which are used almost exclusively on its Cybershot range. Whichever format you go for, you shouldn't be paying more than £40 for 64Mb or £75 for 128Mb. Don't bother with anything less than 64Mb.

Finally, look out for IBM's Microdrive, a tiny hard disk squeezed into a slightly thicker Compact Flash card. Offering up to 1Gb of space for just £200, it's at least half the price of normal Compact Flash cards and has enough space for hundreds of pictures.

Sadly, not all Compact Flash slots can take the Microdrive so, if you're tempted, look for official certification on a camera. The Microdrive can also be slower than normal cards and eats batteries more quickly too.

Screens
One of the most compelling reasons to go digital is to see your pictures straight away, but some colour screens have extra tricks up their sleeves.

Certain higher-end models feature flip-out and twist LCD screens, which allow you to easily frame your shot, whether the camera's low down or pointing over the heads of crowds. Handy for self-portraits.

Exposure control
Virtually all digital cameras offer exposure compensation to make the picture darker or lighter than the auto settings, but enthusiasts will want more creative control.

Look for the ability to adjust the lens aperture to control how much of the picture is in focus (also known as the depth of field).

Similarly, if you want to be certain you've frozen or blurred the action, you'll need control over the shutter speed.

If you're into long exposures at night, look for a model which can do at least eight seconds and also offers a noise reduction mode. This will eliminate the bright, random electronic blobs which plague long digital exposures.

Flash
The majority of digital cameras come with built-in flashes, with varying capabilities. Beyond highly-variable red-eye reduction modes, look out for 'rear-curtain' options on better models, which fire the flash at the end of a long exposure - great for trailing car headlights or sparklers.

Whatever the mode, built-in flashes are for casual use only. Photographers into serious portraits will want to attach a bigger flash gun, which means choosing a digital camera with a hotshoe mount on the top or some kind of plug for synchronising a bracket-mounted model. Some cameras only work with the manufacturer's own flash guns.

Batteries
Digital cameras typically have battery lives of between one and three hours of solid use.

Since you'll be switching the camera on and off between pictures, this usually translates into one to five days of typical usage. Either way, you'll want to be using rechargeable batteries and also carry spares.

The vast majority of digital cameras fall into two camps: those which take sets of AA batteries and those which take a rechargeable lithium ion pack. Both have their pros and cons.

Spare AAs cost a few pounds, compared to around £40 for a spare lithium pack, and are more widely available.

On the other hand, lithium packs are smaller and lighter than a set of AAs and much faster to recharge. If your camera takes AAs but is only supplied with disposable alkalines, budget for a set of rechargeables straightaway.

Connectivity and cradles
Modern digital cameras are fitted with USB ports to speedily transfer your images onto your PC for storage, manipulation and printing.

Some models can even be directly connected to certain printers, bypassing the PC altogether. All but the cheapest cameras also feature video outputs for making slide shows on a TV.

Cradles are accessories which typically include power and USB connections to your PC. By simply placing the camera in the cradle, it'll transfer your images and recharge your batteries at the same time.

Nice, but no different from manually connecting the USB and power lead directly to the camera yourself.

Happy snapping
Before parting with any money, make sure you actually go into a shop and try out your short-listed models. Pick them up, see how comfortable they feel and whether the buttons fall beneath your fingers and thumbs.

If a camera's too big or heavy, you'll end up leaving it at home. All the features in the world are also no good if they're impossible or frustrating to use.

TOP FIVE DIGITAL CAMERA BUYING TIPS:

TRADITIONAL VS NEW

Today you can buy digital cameras from established camera manufacturers or those more traditionally associated with building computers.

Since digital cameras combine both the old and the new, do either group of companies have an advantage over the other? We spoke to Jessops and PC World to find out.

"A couple of years ago, digital cameras from the IT companies had a clear advantage over models from traditional photographic manufacturers in terms of good looks, ease of use and features," explained Karen Limerick, head of marketing at Jessops.

"However, the traditional players have now caught up in many of these areas and are calling upon their photographic know-how to produce some great cameras using high quality optics."

PC World agreed: "Traditional brands have much heritage in the photographic industry. However, as in many industries, companies are sharing information and technologies to create cutting-edge new devices.

"In this rapidly developing marketplace, synergies have developed to enable things like direct printing from camera to printer."

Limerick believes there's little to choose between the two these days, but sums up with this sensible tip for buyers confused by brands.

"The best advice we can give is to get the camera in your hand and see what feels right to you. That's a far more important factor in deciding which model to choose."