Sensor size

Different types of digital camera use different sized sensors. The larger the sensor, the better the picture quality, though the cost increases too. This diagram shows the common sizes:

Apart from specialised studio cameras, the largest are in full-frame digital SLRs, the next largest are in the more common 'APS-C' format SLRs and Micro Four Thirds hybrid cameras, while the smallest are in compact cameras.

The physical size of a sensor is now more important for picture quality than its megapixel rating. With a small sensor, the image has to be enlarged by much more to produce a same-sized print etc. It's like the difference between small negatives and big negatives in the days of film.

There are also technical problems with small sensors that have high megapixel ratings. The tiny pixels on these sensors are nowhere near as sensitive to light and they produce much more random noise than the larger pixels on bigger sensors. This means the makers have to build in strong noise reduction processes, which gives photos a soft and hazy look.

In fact while the resolution of compact cameras has climbed steadily over the past few years, it's probably fair to say that the actual picture quality has stayed the same or even gone backwards.

The bigger the sensor, the better the picture quality, and the gain in quality is pretty much proportional to the sensor size. The table below shows that you don't need that many megapixels to produce good-quality prints, but that the enlargement factor with small sensors is many times higher. Enlargements of up to 30x are usually fine (indicated in green), but when you go beyond this, the definition starts to suffer. There is a limit to how much any lens can resolve, and how much you can blow up the image it produces.

So megapixels are no longer particularly relevant for compact cameras because they've already reached the point where more isn't making any difference, and in fact may be making things worse.

Because the sensors in digital SLRs are much larger, there is still something to be gained from higher megapixel counts, though even here there are signs that diminishing returns are setting in.

Shutter priority | Mode where you choose the shutter speed

In this mode, you set the shutter speed and the camera sets the aperture required to give the correct exposure. Shutter priority mode is often chosen for action photography where you need to be sure of high shutter speeds, or pictorial photography where you want controlled amounts of motion blur, for example in moving water.

Shutter speed | Not just for 'freezing' subjects

The shutter speed is the length of time the shutter is open during the exposure, and one of the two methods of controlling the exposure (the other is the lens aperture). The camera's shutter is normally closed, but when the picture is taken it briefly opens to let the light pass through before closing again.

Shutter speeds go in a particular sequence, where each is twice as fast as the one before (this 2x step is used with ISOs and lens apertures to in order to simplify exposure calculations). Here's the sequence (there are slower and faster speeds too):

1sec, 1/2sec, 1/4sec, 1/8sec, 1/16sec, 1/30sec, 1/60sec, 1/125sec, 1/250sec, 1/500sec, 1/1000sec

The shutter can be inside the lens mechanism (compact cameras) or directly in front of the film/sensor (single lens reflexes and other interchangeable lens cameras like rangefinders). Shutter speed is an important creative control because it can be used to 'freeze' movement or introduce deliberate movement blur.

With moving subjects like this fairground ride, the usual technique is to use a shutter speed fast enough to freeze the movement. In this case, though, a very long shutter speed of 1/6sec was used instead. Using an image-stabilised lens helped keep the background relatively sharp, while the spinning horses have turned into an impressionistic blur.

SuperCCD EXR | Innovative sensor design from Fujifilm

SuperCCD is a family of sensors developed and used by Fujifilm in its digital cameras. Where other makers opted for a rectangular grid of photosites, Fujifilm designed a hexagonal array which, the company claimed, improved sensitivity and hence high-ISO performance.

Fujifilm's new SuperCCD EXR sensor sticks to the hexagonal photosite array, but a different colour filter arrangement so that same-coloured photosites lie next to each other on diagonal lines. The first camera to use this sensor is the FinePix F200EXR, a compact with a 5x wideangle zoom. The sensor design means images can be processed in three different ways to maximise definition, low-light performance and dynamic range respectively.

This diagram shows the old photosite arrangement (left) and the new EXR arrangement (right). The Fine Capture Mode uses all the pixels for maximum resolution, Pixel Fusion Mode combines adjacent pixels to maximise light-gathering power for improved high-ISO/low light performance, and Dual Capture mode combines exposures from two sets of pixels to produce a high dynamic range result.

The disadvantage of the Pixel Fusion and Dual Capture modes is that because pixels are doubled up, the pictures are only half the resolution. So if the camera captures 16 million pixels in the normal high-resolution mode, you'll get 8-megapixel images in the high-sensitivity and high dynamic range modes.

This is more of a perceived problem than a real one, though. Megapixels are overrated, and 8 megapixels is fine for most needs and the reduction in resolution is well worth it for the extra image quality available in the conditions these modes are designed for.

Tripod basics | Speed and simplicity count most

What's there to know? A tripod is simply a three-legged camera support, isn't it? In reality, though, there's a lot more to it than that. A bad tripod is worse than useless: it's a liability that's not even worth what you paid for it because it never gets used. A good tripod is still giving faithful service long after you've forgotten how much you've paid for it.

Leg design and materials
The size of a tripod, its weight and its rigidity - and also its general usability - are largely tied up in its legs. These may come in two, three, four or even five sections. The greater the number of sections, the smaller the tripod will be when folded. However, while three-section legs are reasonably quick to extend, four-section legs are more of a nuisance and five-section legs (such as those found in super-compact tripods) are such a nuisance you may never use them, or at least avoid using them unless you really, really have to. In addition, the greater the number of leg sections, the more flexible the legs become. The join, or clamp, is a point of weakness. It takes very expensive engineering and materials to make these properly rigid.

Above left is a straightforward three-section tripod. This will give a good compromise between size when folded and rigidity. Above centre is a 'digital' tripod with five section legs and a lighter construction.This is smaller when folded and easier to carry around, and fine for today's lightweight digital compacts or maybe a D-SLR with its standard kit lens. Above right is a heavier-duty 'travelling' tripod, again with five-section legs to make it more compact when folded. Compactness is important, but don't underestimate the extra fuss when setting up caused by the extra leg sections.

Legs come in different materials. Aluminium is the cheapest but also the heaviest. It takes pretty thick and therefore heavy aluminium tubing to make rigid legs. Basalt is a fashionable but expensive alternative, and carbon fibre more expensive still. The advantage of these materials is that they offer the same rigidity with less weight. Do be wary of 'cheap' basalt and carbon fibre tripods, though, because the manufacturing techniques required to make proper use of these materials are complex. Cheap basalt and carbon fibre legs won't properly exploit the strength these materials offer.

Tripod makers spend a lot of time talking about weight, and so much so that it's easy to attach too much importance to this. No tripod is light or easy to carry, and even the heaviest is manageable enough once you set your mind to it. The most important thing is that your tripod should be tough, simple and quick to set up. The Uniloc 1600 is a prime example. It's crude, inexpensive but tough. It's big and awkward to carry, but poetry in motion to use.

Some tripods have leg braces. This looks like a good idea in that it should provide extra rigidity. However, it's often a bad sign. On a giant broadcast TV video tripod you might expect it; on a low-cost stills camera tripod, it's a sign the whole edifice is so flimsy it needs all the bolt-on stability it can get.

Centre columns
A tripod's centre column has two jobs. The main one is to provide a little extra height when the legs are already at full extension, but some tripods go further: if the centre column can be rotated in some way, it can also be used as a horizontal boom, which is invaluable for photographing natural history subjects in awkward niches, for example, for table-top photography where the spread of the legs stops you getting the camera right up to the table, and for overhead shots looking down on your subject.

Usually, centre columns slide up and down freely and are locked in position with a knob. This is quick and straightforward. Some cheaper tripods have geared centre columns operated by a fold-out crank. This might look like clever and sophisticated but it's really just cheap gimmickry that's awkward and slow to use. The best design is the simplest, and the quality comes from the materials and the engineering, not the complexity of the mechanism.

Tripod heads
The tripod head is the part the camera is mounted on and which provides the movements. Tripod heads come in two types: ball (and socket) and three-way (pan-and-tilt) heads.

Ball heads are the simplest and quickest to use. The ball mechanism allows movement in any direction when it's released and is then locked in position with a single knob. It's fast to use and very compact, but it's difficult to make fine, precise adjustments in any single direction.

This may not matter much for most types of outdoor photography, but there are situations where it's a profound limitation. One is panoramic photography, where the camera must be rotated horizontally for successive shots, and another is sports photography, where the camera's being turned along the horizontal axis to follow a moving subject. This is where a pan and tilt or three-way head is more suitable.

Three-way heads have three independent axes of movement: horizontal (the 'pan' axis), vertical (the 'tilt' axis) and laterally, which turns the camera on its side for vertical shots and can also be used to quickly level the camera on uneven ground. The two major movements are the 'pan' and 'tilt', hence the common name for this type of tripod head. Three-way heads are bulkier, heavier and slower to set up and use, but the independent axes of movement are sometimes invaluable, particularly for precise still life work or close-ups.

It can be useful to have a quick release (QR) system, but not always. These enable you to flip a catch to release the camera and take some shots handheld, and it's a lot quicker than unscrewing the camera in the conventional way. However, it generally takes longer to fix a quick release plate to the camera than it does to screw the camera to a simple ball head, so it's swings and roundabouts.

Cheaper tripods often come with heads as standard. This saves you money, but they're not usually of good quality. With the better tripod brands you buy the legs and the head separately. This costs you more, but you get to choose the type of head you prefer.

Tripod brands
With tripods you certainly get what you pay for. You should be looking for rigidity, simplicity, ease of use and speed of operation, and you won't get all of these for less than £100 or so. Dealers may stock a number of low-cost 'unknown' brands, but they're not likely to be much good. There are a relatively small number of 'proper' tripod makers to look out for. Velbon and Slik are relatively low-cost but decent brands, with Giottos offers a step up with solid build and innovative design. Manfrotto makes a wide range of good mid-range and pro-level tripods, while sister company Gitzo produces top-quality tripods designed to last for decades but with prices to match. Benbo is something of an outside with a very unusual 'curved bolt' design which offers great flexibility but can be confusing at first, and this same basic design is used in Uniloc tripods. Both are excellent for outdoor natural history work.

Vignetting | Both an aberration and a creative effect

Vignetting (also called corner shading) is where the lens doesn't produce the same brightness at the edges of the frame as it does in the middle. It can also happen when the lens’s image circle is just a little too small for the sensor/film area and the areas furthest from the centre (the corners) appear darker. It’s common with cheaper lenses or zooms at the limits of their performance – wide open and minimum focal length, for example.

You can see it in this shot, where the top corners are clearly darker. It's possible to fix this using software (Photoshop's Lens Correction filter, or DxO Optics Pro, for example), but it's better if the lens doesn't produce vignetting in the first place.

Vignetting can also be applied deliberately using software to produce an old-fashioned effect, though photographers prefer to add it by choice and under careful control as and when they want it.

VR (Vibration Reduction) | Nikon's stabilisation system

Most makers have developed their own proprietary anti-shake system, and Nikon's is called VR, or Vibration Reduction. Any camera movement during the exposure is detected by the mechanism and cancelled out with small, rapid movements of optical elements within the lens. It makes it possible to get sharp shots at shutter speeds 2-4 times slower than normal.

This is a cutaway diagram of the VR system in one of Nikon's SLR lenses. In its smaller compact CoolPix models, the VR may be built into the sensor mount instead.

White balance | Why Auto WB is often the wrong choice

White balance is the colour adjustment offered by digital cameras to allow for different light sources and conditions. It can be left on automatic or adjusted manually. The white balance setting alters the way the camera processes the colour information in the scene. This makes it possible to get natural-looking colours under artificial lighting, for example, where traditional film would produce a very 'yellow-looking' colour cast.

When set to auto white balance, the camera attempts to detect and then correct any colour shift in the lighting. It's not always successful, though, which is why cameras come with white balance presets such as 'daylight', 'cloudy', 'fluorescent' and so on. Here, the colour correction is fixed for these specific conditions, and although selecting the right preset is more trouble, the results are both more accurate and more predictable.

Sometimes, you don't want the camera to attempt to 'correct' the colour of the light at all because it's actually an integral part of the photograph. Here, for example, the colour of the light is very different at two different times of day, but it's a characteristic that you want to preserve, not eradicate. The best solution here is to use the 'daylight' white balance preset because this will reproduce colours exactly as they are and not attempt any correction.

On most cameras it's also possible to calibrate the white balance manually, using a white card or some other colourless object to take a reading from.

So while it's tempting to set the camera to 'auto' white balance and forget about it, this isn't always the best choice:

• The camera may not correct fully for some types of artificial light

• It may correct lighting which shouldn't be corrected

Wideangle lenses | 28mm equivalent or less

This is a lens which captures a wider angle of view that normal or, in the case of a zoom, one which offers a 'wideangle' view at its shortest focal length. 28mm equivalent is considered a 'wideangle', while shorter focal lengths are widere still. Most compact digital cameras only zoom out to the equivalent of a 35mm, which doesn't in fact give a particularly 'wide' view. With compact cameras, then, a 'wideangle' lens is a selling point.

Digital SLRs come with kit lenses which offer a minimum focal length of 28mm, so they're all wideangles. You can get super-wideangle lenses which go wider still, though.

This picture was taken with a super-wideangle 14mm equivalent lens, which is about as wide as conventional lenses go without resorting to fisheyes and obvious distortion.

xD Picture cards | On the verge of extinction

The xD Picture card format was developed by Olympus and Fujifilm but has never really caught on and there are signs that it's now on the way out. When it came out, it was the smallest memory card format available, but today's MicroSD cards are smaller still, so the xD format has no real advantages any more.

For a while, Fujifilm cameras came with combined xD/SD memory card slots so that owners could use both types, but the latest cameras use SD cards only. Olympus, meanwhile, still uses xD card slots in its compacts but now provides a MicroSD adaptor so that owners can use MicroSD cards instead.

Aspect ratios | Not all cameras/sensors are the same

A picture's 'aspect ratio' is its proportions, width compared to height. The sensors in digital cameras have different aspect ratios, but you also course choose the aspect ratio of the picture, of course, by cropping it on the computer. Different cameras over the years have used different aspect ratios:

1. Medium-format film cameras took square 6x6cm pictures on 120 or 220 roll film, though some models took 6x7cm or 6x9cm pictures instead. The square aspect ratio does suit many subjects rather well, though it's often overlooked now. You can use Photoshop to crop any image to the square format, of course.

2. The most common aspect ratio today is the 4:3 ratio of compact digital camera sensors and Olympus and Panasonic's Four Thirds cameras. This is also the aspect ratio of conventional (non-widescreen) TVs, so it's ideal for playing back still pictures or movies on your TV at home.

3. Digital SLRs are different. They have a slightly wider 3:2 ratio. This may go unnoticed much of the time, but it makes a difference when ordering prints online. The standard 6"x4" snapshot size is a perfect match for the 3:2 images from a digital SLR, but not the 4:3 images from a compact. Here you need a print size closer to 6"x4.5" or 5.5"x4".

4. The 16:9 'widescreen' ratio offered on some cameras matches the aspect ratio of widescreen TVs, and it also produces very effective compositions with certain types of subject.

Eye-Fi cards | Wireless connection for your camera

Eye-Fi cards are SD memory cards which contain a built-in wireless transmitter. Providing you’re within reach of a suitable wireless hotspot, you can then transmit your pictures to a photo sharing site or, if you’re at home and have a wireless router, you can send them to your computer.

Eye-Fi Explore cards can also ‘geotag’ your photos. This isn’t done directly within the camera, though – the location information is added to the photos later using software on your computer. Eye-Fi cards don’t contain a conventional GPS receiver. Instead, they look for nearby wireless hotspots and use a service called Skyhook to look up their location.

As a result, coverage is variable and probably not as reliable as conventional GPS right now. It’s quick and simple, though, and as the Wi-Fi card demonstrates, the technology can be fitted into a tiny space.

Eye-Fi cards are very clever, but make sure you camera is Eye-Fi compatible before you invest.

HD movie formats

Today's digital cameras can shoot video as well as stills, making conventional camcorders redundant for many people. And nearly all high-end cameras can now shoot HD video, which means a massive leap forward in picture quality.

There are currently two HD formats in use:

• Standard HD (1280 x 720 pixels)

• Full HD (1920 x 1080 pixels)

Both formats use the 16:9 'widescreen' ratio used by the latest TVs. Full HD offers the best picture quality, but standard HD shot by a good camera is still more than adequate for most casual users and even professional movie makers.

This diagram shows the relative sizes of full HD, standard HD and the 640 x 480 pixel resolution of the movie modes on older compact digital cameras (roughly equivalent to standard TV definition).

Full HD may not always offer the advantage in definition which the numbers suggest, though. This is because some full HD devices use 'interlacing' to achieve this definition. Here, two 'fields' of 540 pixels resolution are interwoven to give the impression of greater resolution.

Interlaced video is indicated by an 'i' suffix. It's common to see HDTV or camcorders described as offering '1080i' resolution, for example.

The alternative is 'progressive' video, where each frame is drawn in its entirety. This gives better results, but is not always possible at the higher resolution. Generally, standard definition devices produce progressive video, which is therefore described as '720p'.

As the hardware and technology improves, there is a move towards progressive video even with full HD, and this would be described as 1080p.

HD cameras shoot video in one of two main formats:

Motion JPEG/AVI/QuickTime

These files can be copied across from the camera's memory card and double-clicked for playback on a computer, uploaded to YouTube or imported into video editing software. It's as simple as that, and much more straightforward than the old days, where the camera had to be connected to the computer so that video could be 'captured' (recorded) in real time. The main disadvantage is file size. You need a big memory card and/or plenty of spare hard disk space on your computer.

AVCHD

This is a file format developed by Panasonic and Sony. It uses a more sophisticated compression system than the Motion JPEG format to produce movie files which take up half the storage space with little or no loss in quality. The disadvantage is that they use a complicated directory/folder structure on the memory card and can't simply be dragged across and double-clicked like Motion JPEG files. You need AVCHD-compatible software to transfer, import and edit these files, though the latest video-editing programs do provide this.

Geotagging

Where digital photos are marked with their geographical location which can then be looked up on a map.

This is usually done with a GPS receiver which may be built into the camera or carried around separately. Apple's iPhoto is just one of a number of programs which can then display the location on a map.

GPS receivers work by establishing communication with a network of satellites orbiting the earth and using the principle of triangulation to work out their precise position from the signals received from these satellites.

There are some problems with in-camera GPS systems, though:

• They use power all the time they're on

• Older GPS systems can take a little time to lock on to the GPS satellites

• GPS doesn't work indoors and can be unreliable outside if you're surrounded by tall buildings or trees etc. The other two issues are likely to be resolved by improved camera design, but the connectivity looks like it will continue to be an issue. As a result, you may find you come back from a trip with some of your photos tagged but not all of them.

Geotagging information is stored within the image file as a pair of co-ordinates using the longitude and latitude system employed by geographers and navigators for centuries. You can find it alongside the image's other EXIF data, which includes things like the date the picture was taken, shutter speed, lens aperture, ISO and so on. Below you can see the GPS information at the bottom of the metadata panel in Lightroom.

But having the location’s co-ordinates is not the same as knowing the name of the place or the district or the country. For this you need some kind of ‘mapping’ tool, and this usually means using a computer and a program like Google Earth. What you do here is 'drop' your photos on to a map (see below), and this simultaneously assigns these map co-ordinates to the image file.

Ideally, though, it would be better to have the camera insert the location automatically as you take the photo, and this means building in some kind of positioning system. The obvious solution here is a built-in GPS receiver. After all, these have proved extremely effective for in-car satellite navigation systems. GPS receivers aren't completely foolproof, though; they don't work well indoors, for example, and tall buildings or forests can cause problems. They also draw a certain amount of power.

Nikon makes a GPS receiver which clips to the accessory shoe of its digital SLRs, and has built GPS into its P6000 compact. The limitation here is that the camera records the co-ordinates but not the country or place name, and some kind of mapping tool is required later to put a name to the place.

However, Samsung's ST1000 compact (above) takes the technology a step forward by incorporating its own mapping system, so that the camera not only records the GPS co-ordinates but the names of cities too.

Cameras with built-in GPS may become more common in the future, but until then there are two ways to geotag your  photos.

One, as we've seen, is to use a program like Google Earth where you manually ‘pin’ untagged photos to a map, which then embeds the latitude and longitude data in the image. It’s crude but effective and easy enough to understand.

The other, more technical solution is to use a separate GPS device or GPS ‘logger’. First, you synchronise the GPS device’s clock with the camera’s, then carry it everywhere you take the camera. Later, you can use GPS logging software to synchronise the GPS log with the digital camera’s images, again embedded them positional data in the photos.

But although geotagging can be problematic, if you're prepared to get more heavily into the technicalities there's a lot you can do to make it a more reliable and more useful process. Take a look at this site, suggested to use by Sebastian Hofer. It's in German, but the Google Translate button at the top right will turn it into perfectly legible English.

Wi-Fi | Or should that be 'Why-Fi'?

Broadly, 'wireless' means any cable-free connection. Wireless technology is used extensively in digital photography for controlling devices or transferring photos. Many cameras can be operated with optional 'wireless remotes', some can transmit pictures wirelessly to printers or even over the Internet to other computers, and some cameras use wireless flash systems.

'Wi-Fi' is used to mean a wireless network which you can use to transmit photos or communicate with other computers. Nearly all laptops and notebooks these days come with built in 'WiFi', or wireless networking, but it's not yet common on cameras.

Nikon's CoolPix S52c (now discontinued) was able to send pictures to Nikon's My Picture Town website where they could be forwarded as emails to other people. Samsung's ST1000 (pictured above) goes further, though, with the ability to email pictures directly.

Some professional D-SLRs have Wi-Fi add-ons that enable photographers to send pictures back to their clients without leaving their location - though most will use laptops which will be able to achieve the same thing much more easily.

The main limitation at the moment is that devices like these need an 'open' wireless hotspot which doesn't require any authentication. Most hotels, restaurants and other public buildings have 'closed' networks which only become available on payment of a fee, and then require an authentication process which is simple enough on a computer but more problematic on a device like a camera which lacks a keyboard.

Histograms | The new way to get the exposure right

A histogram is a graphical display of the distribution of tonal values in the image, from the darkest (on the left) to the lightest (on the right). The shape of the histogram can tell you a lot about the image’s characteristics and, indeed, its flaws. If the histogram is ‘clipped’ (cut off abruptly) at either end, this means the photo has missing shadow or highlight detail.

You can use your camera's histogram display, where available, to get the exposure right rather than relying on traditional metering techniques.

There are three places where you'll find histograms:

1. On the camera's LCD when you're composing the shot. Many compact cameras can display a histogram during shooting, and it's worth checking the manual to find out if yours does. Digital SLRs with a live view mode will be able to display a histogram too. You can use the histogram in conjunction with the EV compensation control to get the exposure exactly right.

2. All digital SLRs and some compacts can display a histogram in playback mode too. On digital SLRs which don't have a live view mode, this is your chance to check the exposure. If you need to, you can then adjust the camera's exposure controls and re-shoot.

3. Image-editing programs display histograms too, usually in the Levels dialog (e.g. Photoshop and Elements). The histogram can help diagnose any exposure problems so that you can see what you need to do to fix them. If highlight or shadow detail has been 'clipped', though, it's too late to do anything about it on the computer. You really do have to get the exposure right with the camera.

Handheld meters | Not the dinosaurs you think

Digital SLRs and compacts have fantastically sophisticated metering systems, so why on earth would anyone want to bother with a handheld meter like the Sekonic L-208 (above) any more? After all, it takes ten times the effort and the metering cell is incredibly primitive compared to the sensor in a modern digital camera.

Well, it's true, handheld meters are slow to use. But they have intrinsic advantages which are often overlooked.

• They're separate to the camera. You can walk around, taking meter readings from different things and different angles to build a truer picture of what the lighting is like.

• You take the light readings manually, estimate a suitable average manually, select a shutter speed and lens aperture combination manually, and apply these settings manually to the camera. Yes, it's more work, but it leads you to think properly (and maybe for the first time) about light, exposure, shutter speed and aperture.

• Even a simple handheld light meter like this one does something not even the most expensive D-SLR can, and that is to take an 'incident' rather than a reflected light reading. It measures the light falling on the subject, not the light bouncing off. You can't use it all the time, but when you can, it eliminates one of the single biggest barriers to successful exposure.

This is how simple handheld meters work:

1. First, you need to make sure you've set the same ISO on the meter as you're using on the camera

2. Then you press a button on the side to take a meter reading, which moves a needle on the scale...

3. You then turn the main dial...

4. To line up the pointer with the needle

5. And then you can read off suitable shutter speed and aperture combinations on the dial

6. To take an incident reading, you move a diffuser over the metering cell, then stand by the subject and aim the meter at the camera.

The L-208 is a basic 'match-needle' meter, but it does the job perfectly well. You can also get digital meters which display an EV value which you transfer to the main dial on the same way, and more sophisticated flash meters which can measure flash exposures too.

PAL and NTSC | Less important with the arrival of HD

PAL and NTSC are the two most commonly-used broadcast formats around the world. PAL is used in the UK, NTSC in the US. Digital cameras and camcorders need to produce the right output for the TV they're connected to. The distinction between PAL and NTSC is likely to become less relevant, though, as digital and high-definition broadcasting take over from conventional analogue transmissions – PAL and NTSC are old fashioned 'standard def' technologies.

It's not just broadcast TV which will be affected. It look as if digital devices will increasingly connect to high-definition TVs via digital HDMI cables (below) rather than old-fashioned analogue PAL/NTSC connectors.

Digital cameras and high-definition camcorders now shoot in a variety of digital formats, but you will still need to select PAL or NTSC if you produce DVDs for playback on domestic TVs and DVD players. The movie editing/DVD software will then carry out the necessary conversions.

PAL and NTSC do use different frame rates (25fps and 30fps respectively). Movie editing software can adjust the frame rate when you export, so that if your device captures footage at 30fps (most do), the software can adjust this to 25fps on export using complex resampling techniques. The results won't be quite as good, however, as if you'd shot at 25fps in the first place.

This is reflected in the latest generation of digital SLRs with movie modes. Where compacts almost always shoot at 30fps, these SLRs typically shoot at 25fps (Panasonic GH1) or offer a choice between 25fps and 30fps (Canon EOS 7D).

Metering patterns | Why simpler is sometimes better

A camera's 'metering pattern' is the way it measures the  light values in the scene. In the old days, the meter was a fairly unsophisticated light-sensitive cell that took one overall reading. Modern cameras, though, offer multi-pattern, centre-weighted metering and spot metering.

The diagrams above represent the way in which these three main metering patterns work. From left to right:

1. Multi-pattern metering (the camera's default) breaks the scene down into segments, measures the light in each and then makes an 'intelligent' decision about the type of scene it's looking and the best exposure to reproduce it correctly. Multi-pattern metering is more likely to be right, more of the time, than any other system, but its response isn't easy to predict.

2. Centre-weighted metering is much cruder. It measures the overall light value, like older metering systems, but places more weight on the centre of the image, where the subject (it's assumed) is most likely to be. Centre-weighted metering is more likely to get it wrong, but, if you're an experienced photographer, it's predictable and easier to correct than multi-pattern metering.

3. Spot metering takes a reading from a small area in the middle of the picture. It's useful when there's a big difference in brightness between the subject and the background or between one part of the scene and another. You use it when you want to base the exposure on just a single area. It's easy to get it wrong, though, and not quite meter the area you meant to, or choose an object that's intrinsically light or dark. Spot metering magnifies your mistakes alarmingly!

NiMH batteries improved with new long-life types

Rechargeable AA batteries make sound economic sense, but their rapid self-discharge rate in storage means that they're often dead at the time you most need them. But Sanyo's Eneloop cells represent an exciting new breed of long-life NiMH batteries which could change everything.

The limited storage life of conventional NiMH cells doesn't matter much if you use your camera a lot because the batteries are constantly being charged and used. But if you only use the camera infrequently, you may find that even though the batteries were fully-charged when you put it away, they've run out when you come to use it again.

It's even more of a problem for photographers who like to carry spares. By the time they get to need them, the spares are probably as dead as the batteries in the camera.

Here's a chart from Sanyo showing the difference between an Eneloop battery and one of the company's conventional NiMH cells. The key point is that an Eneloop battery kept in your camera bag as a spare will still be good after months of storage.

Pancake lenses | Magically miniaturise your camera

A 'pancake' lens is an ultra-slim fixed focal length lens for digital SLRs or hybrid cameras like the Micro Four Thirds models from Olympus and Panasonic. Pancake lenses often have a wide maximum aperture too, making them good for low light and shallow depth of field effects.

This is Panasonic's 20mm f1.7, designed for its G1, GH1 and GF1 cameras. It's equivalent to a 40mm lens in 35mm/full-frame camera terms. Olympus has produced a 17mm (34mm equivalent) f2.8 pancake lens for its Pen E-P1 model.

Pancake lenses appeal to photographers looking for smaller camera/lens combinations, the simplicity of a fixed focal length and the faster maximum apertures and superior optical quality. The resolution may be no higher than a good-quality zoom's, but you can expect far less distortion and chromatic aberration.

Lens mounts | Every maker's is different

The lens mount is the mechanism that attaches a lens to an SLR body. It consists of a twist-lock 'bayonet' mechanism to allow the lens to be attached quickly and a series of electrical contacts so that the lens and the body can exchange the information needed for today's high-tech auto-exposure and autofocus systems.

The bayonet mechanism and the electrical contacts are visible in this shot of the Canon EOS 1000D with its lens removed.

Each maker produces its own proprietary lens mount which is incompatible with the rest. You can't fit Canon lenses to Nikons or Olympus lenses to Pentaxes. There may even be some incompatibilities within the maker's own range. Canon's EF full-frame lenses can be used on its full-frame cameras and it's smaller APS-C models. However, the EF-S lenses designed for the APS-C models can't be used on the full frame EOS SLRs.

Manufacturers are constantly developing their camera and lens ranges, and it's always wise to check compatibility with your existing equipment before you buy, or that your existing lenses can take full advantage of the features in the latest bodies, say.

Camera makers only make lenses for their own cameras, but independent lens makers like Tamron and Sigma may offer their lenses in several different mounts. When you buy an independent lens, you must specify the lens mount you want.

Sensor cleaning

How to use 'dry' cleaning for dust, 'wet' cleaning for stubborn spots and smears.

The sensors in digital SLRs do sometimes need cleaning. The usual problem is dust spots, and although many cameras now have dust removal systems which briefly vibrate the sensor (or a filter in front) to dislodge any dust, these are not always effective. Some dust is just too 'sticky'.

Cameras without in-built sensor-cleaning systems are more prone to dust spots, and the image above shows what they look like (dark, diffuse spots).

Sometimes, the sensor can also pick up smears. These aren't as obvious in their effects as dust spots, but can cause subtle streaking effects or reduced resolution and contrast. Smears may be caused by lubricant spraying from the mirror mechanism (a problem on some Canon cameras, illustrated above), or by previous cleaning attempts. If you're not careful when using a sensor swab, you can drag lubricants from around the sensor mount and on to the sensor surface itself.

Depending on the problem (dust or smears), there are two approaches you can take to sensor cleaning: 'dry' cleaning and 'wet' cleaning.

'Dry' cleaning

This is sometimes done with a blower, but often these simply stir up dust inside the camera body and make the problem worse. Usually, a brush is the best solution, but it has to be a special sort. An ordinary brush, like those sold as camera cleaning accessories, is no good because the fibres collect dust and grease over time. They'll just leave the sensor a whole lot dirtier than it was before.

Instead, you need a specialised sensor brush, like Visible Dust's Arctic Butterfly. This uses electrical charge to pick up dust on the sensor surface, and this charge is generated by spinning the brush (it has a battery and motor) for a period of several seconds before passing it gently across the sensor surface. It may take a few attempts to remove any dust, but the risk of contamination or abrasion damage is much lower.

'Wet' cleaning

This may not be enough, and some people find that a dry clean with a specially-designed sensor 'swab' (below) may shift particles that a brush won't. It's more usual, though, to use swabs as part of a 'wet' clean, in conjunction with a specially-formulated sensor cleaning solvent.

Swabs are shaped like paddles in sizes designed to match APS-C or full-frame sensors (make sure you get the right size). They are sold in individually sealed packages and can only be used one. The fluid you use is crucial too. Ordinary lens cleaning fluid is no good; it has to be proper sensor cleaning fluid.

The trick with sensor cleaning is to stop when you've done enough, but it can be pretty hard to work out when that is with the naked eye. It's usually worth investing in a sensor loupe (below), which combines a magnifying lens with small lamps which illuminated the sensor surface.

If you send your camera away to be professionally cleaned, the technicians will be using the same materials and techniques we're describing here. Hopefully, they'll have the benefit of experience and will do a better job than you could, though you can't always rely on that.

One final word of warning. If you scratch your sensor when cleaning it, it's your responsibility and you will have to pay for a repair, whether or not the camera is still within its warranty period.

ISO | High ISOs are fine on SLRs, terrible on compacts

ISO is the measure of a sensor’s sensitivity to light. The numbers are the same as the ISO ratings given to traditional film. The difference is that a film only has one fixed ISO, while you can change the ISO of your sensor from one shot to the next. ISO values go in the following sequence (some cameras offer intermediate values too):

100 • 200 • 400 • 800 • 1600 • 3200 • 6400 • 12800

Each ISO value is twice the sensitivity of the one before, which makes exposure calculations more straightforward because this is the system used for shutter speeds and aperture settings too.

You can increase the ISO in poor light so that you don't have to use slow shutter speeds and risk camera shake. In full auto mode, digital cameras will adjust the ISO automatically with this in mind.

The disadvantages of higher ISOs on digital cameras are not unlike those of high-speed film. You get more noise (similar to film grain) and reduced definition.

The amount of noise you get is directly related to the size of the sensor and the number of megapixels. The small, high-resolution sensors in compact digital cameras produce much more noise at the same ISO than the larger sensors in digital SLRs.

It's like turning up the volume on an old audio cassette because the music is quiet. The music gets louder, but so does the background hiss, and the overall quality is pretty poor.

You can see that in this example where a small section has been blown up to show the image quality at ISO 100 (left) and ISO 1600 (right). Compact camera makers are constantly increasing the maximum ISO values on their cameras, but only at the cost of plummeting picture quality - no matter what the claims!

The two big problems are small sensors and high megapixels ratings. That's why digital SLRs are so much better at high ISOs than compacts. The sensors are far larger, yet the megapixel ratings are much the same.

Nikon's D3 and D700 are perfect examples. Both have full-frame sensors, but 'only' 12 million pixels. The results is truly astonishing high-ISO performance. The picture above was shot at ISO 6400, yet the enlargement shows that the picture quality is still excellent, with very little noise.

RAW files | Useful, but not always better

RAW files are an image file format available on some high-end compact cameras and digital SLRs. Instead of processing the data to produce a JPEG image, the camera saves the data as it’s recorded by the sensor in its ‘raw’ form, hence the name. The image processing is then carried out later on the computer using 'RAW conversion' software supplied by the camera maker or built into third-party programs like Photoshop, Aperture or CaptureOne.

Adobe Lightroom includes integrated RAW conversion tools which offer highlight recovery, post-shoot white balance adjustment and more. But as well as offering the potential for increased flexibility and quality, RAW files can introduce difficulties, inconsistencies and tricky decisions of their own.

Indeed, there are both pros and cons to shooting RAW:

RAW file pros:

• Certain camera settings can be modified later, notably white balance, colour, saturation and sharpness settings.

• RAW files contain a slightly higher brightness (dynamic) range than in-camera JPEGs and most RAW conversion software can recover this extra detail. It's particularly important for recovering subtle highlight detail.

• Sometimes converted RAW files show subtly better fine detail than in-camera JPEGs. This is particularly true with Canon EOS D-SLRs, as shown by the image below (EOS 400D in-camera JPEG vs RAW file converted in Canon Digital Photo Pro):

RAW file cons:

• RAW files are larger than JPEG files, so you won't be able to store as many on the camera's memory card. These days, though, high-capacity cards are inexpensive and this is seldom a major issue.

• If you use third-party programs like Photoshop to process RAW files, you will not get the same custom colour settings as the camera provides, or exactly the same colour reproduction. For example, pictures you take in the camera's black and white mode will appear in colour in a third-party program because these camera/maker specific settings are ignored.

• In-camera JPEGs sometimes offer better or more accurate colours than third-party RAW converters do with the RAW files. This is because the in-camera processing is precisely tuned to that particular camera's sensor and firmware.

• Makers' own RAW conversion software will preserve the camera's colour settings but may not offer the same highlight recovery and other features of third-party programs.

• It can be difficult to incorporate the makers' own RAW software into your workflow if you're using Lightroom or Aperture, say, unless you carry out the conversion before importing your pictures (which sacrifices much of the flexibility of RAW files).

• Each new camera brings a new and unique RAW format, and it typically takes weeks or even months for third-party software vendors to introduce support for new cameras.

• Different RAW converters produce different results, in much the same way that old-fashioned film developers did. You may find a particular converter does a great job with one camera make, but does less well with another.

• RAW files enable you to postpone some picture settings (e.g. white balance) indefinitely. This is not always a good thing because it's easy to fall into the trap of constantly re-processing files to see if you can improve on the result, or never quite settling on a 'finished' version.

• RAW files are not suitable for distribution. You might be able to open that particular format with your conversion software, but others might not. For publication, circulation or display, you do have to convert them to another format first.

HDR modes in cameras | Only half way to the 'HDR look'

High Dynamic Range is a technique for capturing a much wider brightness range than the sensor could normally record. It's done by taking two shots at different exposures and then combining them. This is usually done using software, but some cameras have HDR 'double-shot' modes built in.

The Pentax K-5 is one example, and Ricoh's CX4 compact is another. But there are a couple of provisos:


• The camera mustn't move between exposures. Ideally, you should put it on a tripod

• The effects you get won't be like those you see in magazines. The camera's aiming to record the maximum possible brightness range, not produce that characteristic 'HDR' effect with dark skies and bright shadows. For that, you still need software.

HDR images straight from the camera will tend to look very 'flat', and their aim is simply to record a full range of tones. If you want shots like this one, you still need to do some work on the computer.

Micro SD | The same but smaller

Micro SD cards are the tiny memory cards found in most mobile phones. What's surprising is not just the tiny size, but the fact that they're available in much the same capacities as standard SD cards and at similar prices.

This 4Gb Micro SD card looks big enough here, but is actually the same size as your little fingernail. So why should Micro SD cards find their way into cameras? Olympus seems to have accepted that its xD Picture card format has a limited future, and in its latest compacts it includes an xD/Micro SD adaptor. The adaptor's in the shape of an xD card (which Olympus compacts still use) but it has a slot for pushing in a Micro SD card.

It's a smart move because these are cheaper and more plentiful than xD cards. For example, a 4Gb Micro SDHC card currently costs £10 or less.

But instead of getting a Micro SD card on its own, look out for adaptor bundles like the Kingston 'Mobility' packs. The pack illustrated includes a 4Gb Micro SD card, a standard SD adaptor (so that you can use it in cameras that use standard SD cards), a Mini SD adaptor (which may be more useful in the future) and a USB stick adaptor, so that you can use your Micro SD card as a USB flash drive. Ours cost £16 from Staples, but you can probably do better.

Face, smile and blink detection

Face detection allows the camera to base the exposure and focus on a person's face, and some systems include smile detection and blink detection too.

Face detection is undeniably clever. Born out of the slightly creepy biometrics industry, it's way of identifying the characteristic shapes of the human face in an image. The camera can then set the focus and exposure to reproduce these faces perfectly in your photos. Early face detection systems were pretty slow and unreliable, but today's cameras can pick out faces quickly and reliably, identifying them with a rectangular frame which can even follow them around if they move or if you change the camera position.

Face detection looks like it works, and it sounds like it ought to be useful, but does it really bear close scrutiny?

For a start, does it really produce better pictures of people? Yes, it ought to, of course, but has anyone actually demonstrated that it does? After all, a camera without face detection is perfectly capable of finding the correct focus point (usually the subject nearest the camera) and the correct exposure (producing a pleasing rendition of the whole scene, and not just a single face).

There ought to be a word for technologies like this, which so obviously ought to work by the very principles involved that no-one bothers to prove it.

But there's more. What happens if there's more than one face in the frame? Camera makers proudly list the number of faces their cameras can identify in a single frame, but don't address a rather obvious and central problem: which one is the camera going to pick, and what can you do about it if it's not the one you want? A few cameras allow you to change the 'chosen' face (laborious and time-consuming), while others may enable you to register 'favourite' faces and give them priority in the future, but already we're moving away from spontaneous, casual photography into something much more complex and involved.

And that's before we've even started on smile and blink detection, features which are now becoming common on digital compacts. Again, it's an idea which has such obvious merit it's seldom questioned. But look, here's how it works:

With smile detection, the camera won't take the picture until your subject is smiling.

Nice idea. We've all got pictures of people frowning, grimacing or looking the wrong way when we wanted them to be smiling at the camera instead. Normally, you'd take a few shots to be sure (it's what digital cameras are good at - instant playback). But with smile detection, the camera doesn't actually take the shot until it sees what it considers to be a smile. Now even assuming the camera can get this right, it produces another, much larger, problem. You don't quite know for sure when it's going to take the picture. And if there's one central, crucial thing about photography it's timing. You absolutely have to know the camera's going to take the picture at exactly the moment you want it to. Without that, you're not a photographer, you're a passenger. A digital camera's shutter lag is bad enough, but face detection adds unpredictability to delay.

With blink detection, if the camera detects closed eyes it takes another shot a moment later.

Again, it's a nice idea. If you actually need it. But here you don't quite know if the camera's finished taking pictures, and it's not very clear what's going to happen if it's a group shot and one person is blinking but the rest aren't.

Some makers are taking it further still, with self-timer modes which only start when a new face (yours) enters the frame. The idea is that it gives you time to get in the frame yourself and doesn't start the countdown until you do. But what's so hard about ordinary countdown timers? You know what you've got to do, you've usually got more than enough time to do it in, and you know when the camera's going to fire. Why make it complicated? (Except, perhaps, to sell more cameras.)

The point about face detection, smile detection and blink detection is that they all leave you and your subjects uncertain about what the camera is going to do, when, and why. Many of the best portraits are candid shots taken in unguarded moments, and any imperfections are part of their charm.

What face detection, smile detection and blink detection do is attempt to perfect portrait shots using a set of perfectly reasonable-sounding processes which, however well-meant, are likely to turn your people shots into deadened, uncertain and uncomfortable encounters.

Surely what we all want is a lot simpler: a camera that it does exactly what you expect it to at exactly the moment you want it to. Face detection technologies, however reasonable they may sound, are taking us in exactly the opposite direction.

Superzooms | Longer range, lower standards

A 'superzoom' is generally reckoned to be a camera or a lens with a focal range of 10x or more. In other words, its maximum focal length is 10x its minimum focal length. The advantage is that you can tackle a wide range of subjects with a single camera or lens, though there are issues with image quality (see below).

This is the Olympus SP-590UZ. It's a typical 'superzoom' camera. It's a compact with a small sensor and a non-interchangeable lens which has a 26x zoom range, covering a focal range equivalent to 26-676mm; in other words, from extra-wideangle to super-telephoto. The quality from the small sensor is OK at low ISOs but deteriorates quickly at higher settings. Nevertheless, the low cost compared to a digital SLR, the range of photographic controls and the huge versatility makes this a popular kind of camera.

But although superzooms like the SP-590UZ are powerful cameras, they're not especially compact. You certainly wouldn't be able to put one in your pocket. For this, you need a 'superzoom compact' like the Panasonic TZ10.

The TZ10 has a 12x zoom equivalent to 25-300mm. You sacrifice the very longest focal lengths, but these aren't used that much anyway. And in return you get a camera which is not much larger than a regular pocket-sized compact. In many ways, then, a compact superzoom is more practical.

You can also get 'superzoom' lenses for digital SLRs. This is the Tamron 18-270mm VC, which boasts a 15x zoom range that's currently the longest for a digital SLR lens, and it covers a focal range equivalent to 28-420mm. The 'VC' stands for Tamron's Vibration Control image stabilisation system. Some kind of image stabilisation system is essential for any superzoom lens or camera.

Superzooms are amazingly versatile, but there are some significant issues:

• Loss of sharpness at longer focal lengths. People often buy a superzoom for its extra focal range, only to be disappointed by the sharpness. This is quite normal, unfortunately, though the best examples can still yield acceptable results at full zoom. The sharpness at short-medium focal lengths is fine.

• Distortion. With a standard zoom you expect a degree of barrel distortion at the wideangle end of the zoom range and pincushion distortion at the telephoto end, but superzoom lenses are usually a lot worse.

• Chromatic aberration: Generally, a superzoom will show higher levels of chromatic aberration (colour fringing) than a normal superzoom at most focal lengths, but at full zoom it can be particularly bad.

• Size and weight: This doesn't affect compact superzoom cameras particularly, but it is an issue with superzoom lenses for SLRs. The Tamron 18-270mm VC is compact for its type, but it's still a monster, especially when extended to its full zoom.

EVF | Electronic viewfinders have cons as well as pros

Electronic viewfinders are used on some cameras where an optical viewfinder would be impractical or undesirable. In the past, the quality of EVFs has been pretty low, but Epson has announced a new 800 x 600 pixel screen which could help change all that.

The point about the Epson display is that it has much higher resolution than usual. Most EVFs have just 0.23 megapixels and look pretty grainy, but this one has 1.44 megapixels and should look much sharper and smoother, helped by an 'analog driver' which produces smoother colour gradations.

This new technology could be highly significant for two types of camera: superzooms and hybrid D-SLR replacements.

Digital compact cameras with long-range zoom lenses, like this Nikon P90, cannot be fitted with optical viewfinders because they do not have an SLR viewing system, and the zooming range is too great for a separate, linked viewfinder. Instead, you get a second, smaller LCD display which you see through the viewfinder eyepiece. This is basically another, smaller LCD, just like the one on the back. Usually, the resolution is too low for accurate focussing or examining fine detail.

The other application for high-resolution EVFs is in hybrid D-SLR replacements like the Panasonic Lumix G1, above. Although it looks like an SLR, the G1 has no mirror. Here, you can see straight through to the sensor itself. During normal viewing, the image is formed on the sensor and transferred either to the LCD on the back or to the electronic viewfinder.

EVFs allow cameras to be smaller, more sophisticated and yet mechanically simpler. There are some serious drawbacks to EVFs, though, which affect the relative strengths of hybrid cameras versus D-SLRs:

• Even the latest high-resolution EVFs lack the visual clarity of an SLR's optical viewfinder

• EVFs consume much more power than optical viewfinders, which usually have a few status LCDs

• Conventional optical viewfinders get their illumination from the subject itself, so their brightness always matches the conditions. EVFs, however, can get swamped in very bright light or prove overpowering in dimmer conditions, even with automatic brightness adjustments