Compact digital cameras buying guide

Cut through the jargon with our guide to buying the best compact digital snapper.

It doesn't matter how much you spend on a camera: it remains, at heart, a simple device that measures the incoming light. A lens, a sensor, a shutter between them... It all sounds deceptively straightforward, until you start to consider exposure, effects, resolution and the myriad stats and features with which their makers love to bombard us.

Resolution

The one thing most buyers look at first is probably the last thing you ought to consider: resolution. Camera manufacturers are renowned for selling their wares on the size of their output, diverting our attention from what really matters -- the size of the sensor.

Each sensor is an intricate collection of 'photosites'. These are sensitive elements that measure the amount of light falling on them, like the cells that activate solar lights when the sun goes down. By laying a red, green or blue filter on top of each one, they selectively filter out all but one colour on each site, arranged in a pattern across the face of the sensor.

By reassembling each of these individual pieces of colour data, the camera rebuilds the scene before it and writes the results to its memory card. Each photosite can only accept a certain amount of incoming light before it becomes overloaded, with the physical size of the photosite defining the point at which overload occurs. The smaller the photosite, the sooner that is.

A full-frame dSLR (digital SLR) sensor is 36x24mm, giving a surface area of 864mm2. In a typical compact camera, it's usually around 5x4mm, for a total surface area of just 20mm2, into which the manufacturer may still have crowbarred teens of megapixels.

For this reason, images from a dSLR will usually suffer from less interference than those from a digital compact, where the signal to noise ratio (wanted vs unwanted data) will be lower: less signal, more noise.

Don't always buy the highest megapixel compact you can afford. 10 to 12 megapixels is more enough for printing at A3, while even a smart phone snap is up to the job of filling A4 with plenty of crisp detail.

Zoom

The longer the zoom, the closer you'll get to your subject, but take it too far and you'll start to have problems, key among them stability.

Push a 14x zoom to its limit and you'll be fixed on so small a portion of the scene that the slightest movement on your part will throw the whole thing out of the frame.

Camera manufacturers' answer to this is stabilisation. Always check that this is a feature on any long-zoom digital compact, and wherever possible look for optical, rather than digital stabilisation, which moves the lens or sensor rather than enhancing the image after it's captured.

Aperture

The length of the zoom can also impact the relative brightness of the lens.

The size of the opening through which light reaches the sensor affects two things: how much light enters the camera, and how much of the scene is in focus. This focal area is known as the depth of field, and is measured along the horizontal distance towards and away from the lens.

Aperture is expressed using f-stops. The smaller the f-stop number, the more open the aperture will be, the more light will enter the camera and the shorter the depth of field. The higher the f-stop, the less light will enter, and more of the frame will be in focus.

A high-end lens on a dSLR might have a range of f/1.2 to f/22, allowing for short-focus portraits at the wider end of the scale, and long-focus landscapes at the other. A digital compact, on the other hand, will be closer to f/3.3 at the wider end of the zoom and f/5.5 at the widest full telephoto setting, with each narrowing to less than the f/22 seen on the dSLR.

The further you can push this scale in each direction when making your choice, the better. It'll give you more creative freedom and, if you can source a wider aperture at the lower end of the scale, help your camera to perform in lower light without increasing its sensitivity.


Left: A wide aperture gives us a shallow depth of field. Right: A narrow aperture maximises the depth of field.

Sensitivity

Sensitivity describes the sensor's ability to accurately measure the differing levels of light falling on its surface. The measurement we use -- ISO -- is a hangover from the days of film photography, where ISO 100 required higher levels of light but produced a finer-grainer image than so-called slower films, such as ISO 200, 400 or 800. These required progressively less light to accurately expose a frame, but introduced more and more grain as you stepped up the scale.

We still use the ISO scale when shooting digital images, only now the visible grain is replaced by increased electrical noise as we increase the sensitivity. Look for a camera that has a low effective minimum sensitivity, wherever possible ensuring that the scale starts out at ISO 100 or lower (ISO 80 is becoming more common) with 'compensation' measured in 1/3 stops, on a scale of at least -2 to +2 EV (exposure value).

Compensation allows you to selectively boost or reduce the amount of light collected by the sensor by adjusting its sensitivity. Increasing the exposure value towards +2.0EV increases the amount of recorded light without increasing the ISO setting, and vice versa, allowing you to lighten darker scenes or darken off overexposed skies to enhance the overall balance of your results.

Stopping down sensitivity, exposure and shutter speed to the minimum on each scale is also an effective route to taking long exposure images on a digital compact.


Left: Low ISO for a finer result. Right: High ISO for better low light performance, but with added grain.

Shutter speed

Shutter speed speaks for itself, measuring the amount of time the sensor is exposed to the incoming light. Selecting a shorter shutter speed allows you to freeze movement within the frame. Leaving it open for longer softens moving water, and introduces a feeling of speed if you use it to capture sports events or moving traffic while panning in line with the subject. The result with be a sharp focus against a blurred background.

Look for a camera with a shutter speed ranging from around 1/4,000-of-a-second for use in the brightest conditions, to one second or more for use at night. To effectively capture fireworks and night scenes, you'll want to push this even further and look for exposures of around eight seconds so that you can avoid leaning too heavily on higher, noisier sensitivity settings or exposure compensation.

Longer exposures introduce the same problem as longer zooms: you need to be sure you can keep the camera still, preferably without relying on the camera's built-in anti-shake features. Overcome this by investing in a cheap tripod such as the Joby Gorillapod (see image below), set your camera to a long exposure and use the self timer to automatically fire the shutter.


Self timer and facial recognition

For greatest flexibility, look for a camera with both 10- and two-second self timers. The former gives you time to settle the camera and run into a group shot yourself, but it's far too slow for the longer exposures described above, seriously cutting down the number of snaps you can take in a minute.

As a bonus, choose your camera from one of the growing selection featuring both blink and smile detection, which take a picture not on the basis of time, but when your subjects look happy, all have their eyes open and are facing the camera.

Modes

Modes, scenes and effects all combine to change the finished look of your pictures. All digital compacts have a fully automatic mode that you'll use for most of your shooting, leaving the camera to set the aperture, sensitivity and shutter speed on your behalf. This is usually marked on the mode dial as 'A' or 'iA', or with a picture of a camera, often in green.

For greater flexibility look for a camera that has dedicated shutter and aperture priority modes. Shutter priority lets you specify how long the shutter should stay open, depending on whether you want to freeze the action of fast-moving subjects or capture low light scenes over a longer period.

Aperture priority lets you control the depth of field by opening or closing the aperture and leaving the shutter speed part of the equation in the hands of the camera.

In either instance, ensure that the controls for tweaking the aperture or shutter speed are immediately accessible, without having to trawl the menus, so that you can make on-the-spot changes whenever the situation requires.

Allied to this are scene modes, which are pre-configured settings specific to each camera that balance each part of the exposure equation for a specific use. Sometimes these are available directly on the mode selector dial on the top or back of your camera, but most often they're hidden within the menus. Common scene modes include portrait (wide aperture, sometimes with a slight soft focus), landscape (narrow aperture, sometimes with slightly boosted greens and blues) and fireworks (long exposure and/or higher sensitivity).

Beyond these, the only limit is the camera manufacturer's imagination, with pet portrait, food, museum and children modes among the less esoteric. A camera with several scene modes in its arsenal makes a great starting point for beginners who want to be more creative with their photography but don't know how, as you can examine how the camera has changed its settings and copy them yourself at a later date without resorting to the pre-set scenes.

Finally, cameras that feature effects apply a basic Photoshop-like filter to your shots. These should should be used with care. The more processing that is applied to your photo at the point of capture, the less chance you have of extracting a true representation of the original scene at a later date. Effects, then, are good to have, but don't let your buying decision hinge on either their number or their promised results.

Movie mode

Any compact worth its salt now features a movie mode, usually saving videos in either AVI or AVCHD format (the latter most often found on Sony and Panasonic cameras, as they jointly developed the format).

AVCHD is the best format for DVD and TV playback; AVI for use on the Web, although if you're prepared to spend a little time editing your results in Windows Movie Maker or iMovie (for which you'll need an additional add-on to import AVCHD files) you can repurpose either for the alternative playback device.

In the same way that manufacturers have a tendency to brag about the resolution of their cameras' stills, there's a tendency to trumpet 'HD quality' video on digital compacts.

This describes the camera as having a minimum video resolution of 1,280x720 or 1,920x1,080 pixels, but says nothing of the actual quality of the finished result. You'll soon forget all about resolution if the level of compression applied to the video stream is so high that the results lack clarity, so balance resolution with compression. Where possible, download a camera's user guide from the manufacturer's website (look in the support section) and hunt out the video data rate and compression figures. High data rates and low compression are key.

While you're there, look for additional features like anti-shake, to smooth out knocks and bumps on long handheld shots and footage filmed while you're moving, and wind noise reduction to tame a wild soundtrack.

Battery life

You'd be hard-pressed to find a camera running off AA batteries these days, so don't expect to pick up replacements if yours runs dry when you're out and about. Unless you're happy to carry a spare battery at all times, look for a device that will give a full day's shooting on a single charge and then recharge in two to three hours.

Battery life is usually measured in terms of shots; look for a life of around 200 to 300 shots per charge. However, you're unlikely to take this many pictures on a single charge, as some of the power will be consumed reviewing pictures and using the menus and settings as you go along.

All manufacturers report remaining battery life in a different manner, with most adopting a dynamic battery icon that slowly empties over time. Sony's InfoLithium battery system, which is an optional add-on for most of its cameras, instead estimates remaining battery life in minutes, based on current usage.

Closing advice

If all of this sounds like too much to consider when all you want is a £100 snapper for taking to the pub and using on the beach, use the Flickr Camera Finder, which catalogues the mass of images uploaded to its servers in terms of manufacturer and model.

Once you've found a camera you like the look of, dig down through the categories to find representative examples of the kind of pictures you're most likely to be taking yourself. A thorough review of the results is the best buying advice you could ever hope to get.


Ready to find your camera? Get started with our always-current lists of the best compact cameras and the best cameras overall.

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Cameras
About the author

    Nik Rawlinson has been writing about tech since Windows 95 was looking distinctly futuristic. He is a former Editor of MacUser magazine and one-time scribe for Personal Computer World. Nik is a freelance writer and is not an employee of CNET.

     

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