When choosing a digital camera, you need to consider the four main components of your imaging system: the optics which get the image onto the sensor, the body which allows control over the system and store the images, and the software and transfer system which gets the images across to a computer or printer for output.

Optics

The lenses which get your image onto the sensor are perhaps the deciding factor in which kind of camera you will need. There are two main types of digital camera, based on similar ideas from 35mm cameras - compact zooms and SLRs.

A compact zoom digital camera is an all-in-one body with a relatively small, integrated lens system placed very close to the 'film'. This design allows for higher quality at lower cost compared with single lens reflex (SLR) designs, which allow you to change lenses.

Compact zooms, like their 35mm and APS cousins, are designed for portability and ease of use, and will perform very well for a wide range of typical applications such as friends and family pictures and holidays. They are also particularly useful for business applications such as recording progress on building sites, photographing houses for an estate agent's catalogue, creating a catalogue for an auction, and so on.

As the sensor in a compact zoom is much smaller and closer to the lens than in a 35mm camera, the measure of your lens - its focal length, starts off much shorter - typically 4-6mm. Look out for a significant range of magnification on the lens - 3x optical is a good level. Make sure you look at the optical zoom, rather than the digital zoom (see below) - this is the measure of the actual range of your camera lens.

Most compact zoom cameras also have a feature called digital zoom, which is where the electronics in your camera further magnify the central part of your image to create a further 3x or more of zoom. Since this works with a finite amount of actual image data, the quality of the final image cannot be fully maintained at high levels of extra zoom, so bear this in mind.

For semi-professionals and professionals, the familiarity, technical and artistic flexibility of a single lens reflex is a must. The major makers of 35mm SLR systems now have affordable digital systems which slot right in with your existing lens and accessory colllection. At this end of the market, your own optics are reusable as is, all you have to do is change your 35mm body for a digital one.

One thing to remember when buying a digital SLR is the sensor size - all currently available models have sensors much smaller than 35mm film. This leads to an effective lengthening of your lens focal lengths, for example a 50mm lens on a Canon D30 (which has a sensor size 1/1.6 of a 35mm frame) goes to 80mm. This has both advantages and disadvantages - your telephoto lenses suddenly get much longer (e.g. 300mm becomes 480mm!) but your wide-angle lenses become standard lenses (28mm becomes 45mm).

Resolution

The next thing to look at on your digital camera is the resolution of your image sensor. This is typically measured by the number of pixels (picture elements) or 'dots' present on the chip. The principle is similar to the computer screen you are reading now - it may have 800x600 (480k) or 1024x768 (768k) pixels displaying the page you're looking at.

Nowadays, image sensors come with megapixels, ranging from 1-2M for entry level cameras to 6M or more for cameras like the Canon 1d and Nikon D1. The more pixels you have, the closer to the quality and feel of film you will get, so get as high a resolution as you can afford for your needs.

One thing to remember when looking at resolution is that your image files become bigger when they contain more pixels. This means that your storage (memory card, memory stick or disk) will store fewer images at a time, and the electronics in the camera will have more data to deal with, requiring more processing power.

Finally, there are now two types of image sensor - CCD and CMOS. These are just microchip design technologies, but the main differences between them are size and cost. CCD-based systems are by far the most common, and this means that a 3-million pixel CCD is much smaller and less expensive to produce than a 3-million pixel CMOS. Many people believe that CMOS is a better, more film-like technology, but so far it has only appeared in cameras like the Canon D30 and D60.

Body Features

The images you capture on your camera are only going to be as good as your ability to control and manage the process of taking and storing a picture. Advances in both 35mm and video cameras are quickly introduced into digital still cameras, so expect to see a huge number of features and functions on even an entry-level model.

One very useful feature on many cameras is an LCD screen for previewing and reviewing your images. You can very often use this instead of a viewfinder to frame and point your camera, and some screens angle out from the body like a video camera, allowing you to look over a crowd or round a corner for hard-to-reach shots. Look out for the size and resolution of the screen - the higher these are the more faithfully the image will be shown and the better the feedback they provide. Be aware that screens can contribute significantly to the battery life of your camera - take advice on how to save power when possible.

Many cameras have the ability to capture short video sequences just like a camcorder. Since the memory capacity is much less than a tape, these will be quite short compared to a DV camera, but still useful for getting that extra dimension of motion.

The onboard editing facilities are important when memory capacity is tight, allowing you to review and discard unwanted shots while out on the road, reclaiming the space for the pictures you do want to keep.

With the number of features on your camera, make sure the menu system is relatively easy to find your way around. Most modern cameras have a huge investment in the usability of their menu systems, but have a tryout to make sure you are comfortable with the interface.

In a competitive market, each new camera comes out with some new feature to differentiate it from its rivals, so take your time to find the one with the feature set you are most likely to find useful. Talk to our staff about what subjects you will mostly be using, your experience with photography, and we will help you find the best fit to your needs.