photo-facts.blogspot.com

Accessory shoe

2011-11-09T17:45:00.000Z

This is also called the 'hotshoe', and it's where you slide in an external flashgun or, in the case of some cameras, other kinds of accessory.

Neutral density filter

2011-09-29T08:08:00.002+01:00

Neutral density filters reduce the amount of light entering the lens without altering it in any other way. It sounds an odd sort of thing to do, but ND filters are useful if you want to use slow shutter speeds for creative blur effects. In poor light, this isn't a problem because the shutter speeds will be lower anyway. But in bright light you need an ND filter to reduce the intensity.

You can also find 'neutral density' filters in some compact cameras, where the lens aperture adjustment may not be enough on its own to cope with really bright light. This is because, for technical reasons, the small lenses in compact cameras don't offer the small lens apertures you get with digital SLR and compact system camera lenses. In these cases, the neutral density filter is activated automatically.

Contrast filters

2011-09-29T08:05:00.000+01:00

'Contrast filters' are used in black and white photography to change the way different colours translate into shades of grey. Although the pictures are black and white, the film (or sensor) is sensitive to all colours of light, and it simply converts these colours into different shades. And by using filters which block certain colours but allow others through, it's possible to make those colours appear as a darker tone in the photo.

For example, red is the complementary (opposite) colour to blue, so by using a red filter, you block most of the light from a blue sky. As a result, blue skies come out almost black to produce a dramatic, high-contrast image where any clouds stand out vividly.

This is fine for dramatic, high-contrast images, but a little too strong for most landscape photographs. Here, photographers often prefer a yellow filter, which still darkens blue skies, but not quite as much. At the same time, because vegetation contains a high proportion of yellow, a yellow filter lightens grass, trees and other greenery.

It's also possible to get yellow/green filters which are designed to enhance greenery just that little bit more, or orange filters which have an effect somewhere between yellow and red, so that you get more dramatic skies without the excessive contrast of a red filter.

Contrast filters are used less often with digital cameras because it's easier to shoot in colour and then choose a filter effect digitally when you convert it to black and white. You can do this using the Channel Mixer in Photoshop, for example, or with a dedicated black and white plug-in like Nik Silver Efex Pro 2.

Bits and bit depth

2011-05-11T08:57:00.000+01:00

'Bits' are important in digital photography because they affect the brightness (dynamic) range of the picture you capture and the ultimate quality of any image you manipulate on a computer. You'll often hear manufacturers talking about the bit-depth of their sensor or processing system (e.g. '14-bit processing'), and many photographers prefer to work with '16-bit' images rather than the 8-bit images usually captured by digital cameras.

But there is some confusion over bit-depth and its practical significance, and it does actually mean two different things, depending on whether you're talking about image capture or image editing.

'Bits' are the fundamental particles of computing. A 'bit' has two values; it's either on or off, but when you put lots of bits together, they can convey much more information. There are lots of other places to read up on the computing science behind this, but the relevance for digital photographers is that the colour and brightness values in the pixels which make up a digital image are described using 'bits'.

Photos are split up into three colour channels: Red, Green and Blue. When photographers talk about 'bits', they're usually talking about individual channels. So an 8-bit image is one which uses 8-bits of data to describe the tones in each channel, and a 16-bit image uses 16 bits per channel.

Anyway, what's confusing is that while higher bit depths mean better quality, the way it works depends on whether you're talking about image capture (what the sensor records) or image editing (the point where you get to control what the image looks like).

Image capture
Photographers often relate bit depth to dynamic range, or the range of brightness values the camera can record, in other words. The output of the camera's sensor is often expressed in terms of its bit depth, and in this context, bits translate directly into brightness values. The greater the number of bits, the greater the range of brightness values the camera is recording.

If you're photographing a subject with a high brightness range, you might expect to lose some of the darkest shadow detail and the brightest highlights. The diagram simulates the difference between a sensor that captures 12 bits of data, like a high-end compact camera, perhaps, and one that captures 14 bits of data, like a good SLR. The 14-bit sensor has captured the last bits of detail at the ends of the histogram, where the 12-bit sensor has 'clipped' them and won't record the extra data.

What happens now is that the camera processes this data to save either a RAW file or a JPEG. The RAW file will contain all 14 bits of data, but JPEGs can only store 8 bits of data.

This is important. The camera does not then 'clip' the data to produce the JPEG file. That would sacrifice even more of the shadow and highlight detail. Instead, it 'expands' the 8 bits it can use to cover the full brightness range the sensor captured. There's probably a much more technical way of explaining it, but that's basically what's happening.

The bottom line is that you'll get the full dynamic range of the sensor, regardless of whether you save a RAW file or a JPEG. The RAW file may contain a little extra data you can exploit to increase the dynamic range, but it's a small amount that's nothing to do with the basic dynamic range and bit depth principle.

Image-editing
When you get to the image-editing stage, the meaning of bit-depths changes. It no longer describes the brightness range of the image, but the subtlety with which the tones in the image are reproduced.

Normally, digital photos use 8 bits of data per channel. This allows up to 256 different tones, and for everyday photography this is enough to produce the appearance of smooth gradations, especially when the three colour channels combine to produce the image you see.

This is fine until you start applying heavy image manipulations. This can exaggerate the difference between the tones and produce 'banding' or 'posterisation' effects. You do have to push the image quite far for this to happen, but it does happen. What many photographers do, then, is work with 16-bit images instead.

When 16 bits of data are used to describe colour values, the number of possible shades is increased massively (just over 65,000). As a result, images tend to survive heavy manipulation much better because you don't get these banding or posterisation effects. Many serious photographers prefer to work with 16-bit rather than 8-bit images for this reason.

Here's another diagram. On the left is a simulation of how the tones in an 8-bit image are described. The shift in tones is very 'blocky', like a kind of staircase effect, and while you wouldn't normally notice this, heavy editing can exaggerate these steps to the point where it becomes visible. The 16-bit version on the right, though, is extremely smooth, and you're not going to get the same 'staircase' effect, even with heavy editing.

Does that mean you should always use 16-bit files rather than 8-bit? Not necessarily. They take up more space, not every program supports them and it's simply not necessary for photos which only require moderate adjustments.

There are some other things to be aware of:

• You can convert an 8-bit image into a 16-bit image in a program like Photoshop, but there's not much point because this won't recreate the intermediate tones the camera never captured in the first place.

• Cameras can't shoot 16-bit JPEGs, so the only way to get a 16-bit image is to shoot in RAW mode, then convert the files into 16-bit images with your RAW conversion software.

• Even in RAW mode, cameras don't record 16 bits of data (except some medium-format equipment). Most record 12-14 bits, and the RAW converter simply 'interpolates' the extra bits. This doesn't matter too much, because the extra bits you get from RAW files are still a major advantage.

The bottom line
Many photographers associate bit depth with dynamic range, but this only applies at a hardware level, during the picture capture process.

By the time you have any control over the process at all, for example when converting RAW files, the meaning of bit depth has changed, so that now it's concerned with how subtly tones are rendered, not how great a brightness range the image contains.

Zone System

2011-05-11T08:45:00.001+01:00

This is an advanced system of tone control in black and white pioneered by legendary landscape photographer Ansel Adams. The Zone System had and still has many fans, but is technically demanding and not always properly understood.

The scene is split into ten different brightness ‘zones’ from black to white, and the photographer plans the exposure to make sure all ten zones are recorded on the film. The next, crucial, stage, is the development process, where the contrast is adjusted to reproduce these zones in the print, though dodging and burning techniques may also be used on specific areas.

This second stage is impossible with film processed in rolls or cassettes, and the Zone System really only worked with sheet film cameras. It’s difficult to replicate with digital cameras because they don’t have the dynamic range of old-fashioned black and white film, which could record far greater extremes of brightness, a crucial factor in the effective use of the Zone System.

Yellow filter

2011-05-11T08:44:00.001+01:00

A yellow filter is used in black and white photography to enhances skies and landscape shots. Back and white film is ‘panchromatic’ – it’s sensitive to all colours – so if you block one of these colours with a filter it will come out darker in the picture.

It's a standard way of adjusting the tonal rendition of black and white photos. A yellow filter will block a lot of blue light, making blue skies come out darker on the film, but it will let through the yellow and most of the green in a scene so that foliage and vegetation is largely unaffected.

Widescreen

2011-05-11T08:42:00.000+01:00

Many cameras can shoot still photos in the 16:9 ratio, which is ideal if you want to display them on TVs or add them to HD movies on a computer. Some shots, particularly landscapes, work well in the 16:9 ratio. Even so, the 16:9 ratio is not used that much for still photography, because it doesn't match the aspect ratios of common print sizes, and it means cropping off some of the image captured by the sensor either in the camera or on the computer. (Camera sensors come in narrower 4:3 or 3:2 aspect ratios.)

Viewing angle

2011-05-11T08:40:00.000+01:00

The quality of an LCD display isn't just dependent on its size or the number of dots. The viewing angle can be just as important. This is the maximum angle of view for an LCD display. Outside this angle, the display may appear too dark or light to make out properly. A good viewing angle is important for cameras with fixed ('non-articulating') LCD displays. Some newer technologies, like OLED or AMOLED displays, offer particularly good viewing angles.

Tint

2011-05-11T08:26:00.000+01:00

White balance is usually explained in terms of ‘colour temperature’, which runs through red (low temperature), yellow, white to blue (high temperature). Some light sources, though, have an additional green/red component and most digital cameras and software now offer additional ‘tint’ adjustments to allow for this.

Tethered shooting

2011-05-11T08:24:00.000+01:00

Professional studio cameras are often connect to and operated from a computer, and you can do this with some digital SLRs, too. Tethered shooting gives the operator much more control and leaves them free to work with the subject or the props. Some professional-level digital cameras can operate as 'tethered' cameras using software supplied with the camera, or from a third-party company.

Telephoto

2011-05-11T08:22:00.000+01:00

It's a vague term because it can mean anything from the slight magnification of the zoom lens on a compact digital camera to the 8-10x magnification of lenses used by professional sports photographers and the paparazzi. Most lenses these days are zooms, so they have a variable focal range, but it's still possible to classify lenses broadly as 'wideangle', 'standard' or 'telephoto' zooms. This picture was taken with a superzoom camera at maximum zoom (500mm equivalent). The longer the focal length (magnification) of a lens, the more skill it takes to use it. Any camera shake is magnified too, which is why image stabilisation systems are often used to keep the picture steady.

Supersonic Wave Filter

2011-05-11T08:20:00.000+01:00

The Supersonic Wave Filter (SSWF) sits in front of the sensor and shakes briefly at a very high frequency to dislodge any dust particles. Other camera makers use their own, similar system.s

Stop

2011-05-11T08:16:00.000+01:00

This is the old-fashioned term for one unit of exposure value, or 1EV using today's terminology. The principle of exposure calculations is that each step in shutter speed or lens aperture (each 'stop') corresponds to a doubling or a halving of the light value. In this way it's easy to play off shutter speed against lens aperture for creative photographic effects. You can also check different parts of the scene for brightness, and work out, for example, that the ground is two 'stops' darker than the sky. This is useful for more advanced exposure techniques and calculations. Photographers still talk in terms of 'stops' even though the correct term would be 'EV values'.

sRGB

2011-05-11T08:14:00.001+01:00

This is the usual colour space, or ‘gamut’, used by compact digital cameras, digital SLRs, computer screens and desktop printers. It’s adequate for most photographic purposes, though the Adobe RGB colour space is used by some professionals and commercial printers for images destined for magazine and book printing, for example.

Spirit level

2011-05-11T08:13:00.000+01:00

Some tripods and tripod heads incorporate spirit levels to help you get the camera level. Spirit levels are especially important in panoramic photography, where any slight tilt is magnified across the width of the panorama. Here, the spirit level must be in the tripod base; it's essential to have a level platform for the tripod head. Spirit levels may be horizontal (more accurate, but one is needed for each axis of movement) or 'bubble' types (less accurate, but only one is needed).

Some cameras now incorporate 'digital' levels which are displayed on the LCD on the rear of the camera. These help prevent tilting horizons, but only work along one axis and aren't always as responsive or as accurate as conventional bubble levels.

SLR (single lens reflex)

2011-05-11T08:11:00.000+01:00

In this camera design, the image formed by the lens is reflected by a mirror inside the camera, up into a reflecting prism (‘pentaprism’) and on to a focussing screen. You view the image on the focussing screen through the camera eyepiece. The ‘single lens’ part comes from the fact you are viewing and taking the image through the same lens, and the ‘reflex’ comes from the mirror, which flips up out of the way at the moment of exposure so that the image falls instead upon the film or sensor at the back of the camera.

Slave flash

2011-05-11T08:06:00.000+01:00

This is a flash which fires in response to others and is used in studio photography where more than one flash is needed. The flash head has a light sensor which detects another flash at the instant it fires, and this means you don’t have to have synchronisation cables trailing to each flash head.

Skylight/UV filter

2011-05-11T08:04:00.000+01:00

UV filters were popular in the days of film photography because they cut through the UV ‘haze’ in distant views which might otherwise give them a blue tinge (many films were over-sensitive to UV light). The Skylight filter is a slight variation on the UV filter which adds a subtle warm tint to enhance the appearance of landscape shots.

Skylight and UV filters are hardly needed these days because digital sensors seem less prone to UV. But they do have another use - they're an inexpensive way to protect lenses from dust and scratches, and since they don't do any harm, some photographers leave UV lenses fitted all the time for this reason alone.

UV/Skylight filters are always of the round, glass type. Once they're attached to the lens, you scarcely notice they're there, and they don't have a significant effect on exposure.

Signal to noise ratio

2011-05-11T08:01:00.000+01:00

This is the level of random variation in the pixels of digital photos. The pixels (photosites) on sensors record the levels of light falling on them as an electrical signal. However, there’s always a certain level of random background electrical activity which causes extra variations. A high signal to noise ratio means low noise levels, while a low signal to noise ratio means high noise levels.

The signal to noise ratio is affected by the size of the camera's photosites and the ISO (sensitivity) setting. Compact cameras have small sensors and hence small photosites, so their images are noisier right from the start, and this only gets worse if the ISO is increased. Maker use internal noise reduction systems to disguise the noise, and this can have a softening effect on the image.

Digital SLRs and hybrid cameras with larger sensors have larger photosites, so they don't produce anywhere near as much noise. As a result, their images look cleaner and clearer, and the picture quality is much better at high ISOs.

Sidelighting

2011-05-11T07:56:00.000+01:00

The two main characteristics of light are its direction and its 'quality'. Broadly, light can strike the subject from the front (frontal lighting), from the side (sidelighting) or from the back (backlighting). The 'quality' of the light is, for want of a better word, it's 'hardness'. A small light source like the sun or a naked light bulb produces very hard light which produces hard-edged shadows and has a very clear direction. Softer light, such as that you might get from a window, still has a clear direction, but produces much softer-edge shadows which are hardly shadows at all, more shaded areas. The softest light, such as that produced by an overcast sky, casts no shadows and doesn't have a clear direction either. This is an example of strong sidelighting. The small light source (the sun) has produced strong, hard-edge shadows and the direction (from the side) is perfect for bringing out the texture of the stone wall nearest the camera.

Shutter curtain

2011-05-11T07:54:00.000+01:00

Digital SLRs and hybrid cameras with interchangeable lenses use 'focal plane' shutters directly in front of the sensor which consist of ‘first’ and ‘second’ curtains. The first curtain moves aside to expose the sensor and the second curtain moves across to cover it again at the end of the exposure. At higher shutter speeds the second curtain starts moving across before the first curtain has fully opened so that the sensor is exposed via a moving slit rather than all at once. This is the only way to achieve the very high shutter speeds digital SLRs are capable of.

Shutter

2011-05-11T07:48:00.001+01:00

The mechanism that exposes the sensor. The shutter ‘speed’ is the length of time the shutter remains open and is usually expressed in fractions of a second, although in poor light and night photography, exposures may run to several seconds or even minutes.

Shift (perspective control) lens

2011-05-11T07:46:00.000+01:00

A shift lens is used to correct distortion in architectural photographs and sometimes to manage depth of field in studio shots. The lens can be moved upwards, downwards and side to side relative to the camera body. This is used to correct the perspective distortions you get when you’re unable to photograph a subject head-on. Shift lenses are heavy and expensive. One reason is the precise engineering needed to produce smooth and accurate movements, and another is that the lens has to provide a much larger image circle than usual in order to prevent corner shading (vignetting) when the lens movements are used.

Sensor dust

2011-05-11T07:37:00.000+01:00

Dust on the sensor can be a problem with digital SLRs, and it manifests itself as diffuse dark spots which appear in the same place on each image. Compact digital cameras don't suffer from this problem because they don't have interchangeable lenses. The lens and sensor are sealed units that don't allow dust to get in. Digital SLRs do have interchangeable lenses, and dust can get in and settle on the sensor. Some models have in-built 'cleaning' systems which attempt to shake dust free, and these can be effective though don't necessarily provide a complete cure.

There's a dust spot right in the middle of this picture, and while this can be cloned out easily enough in an image-editor, it's a nuisance having to do it time and time again.

Dust doesn't always show up as badly as this. At wider lens apertures, the reduced depth of focus makes spots paler and more diffuse, and if the background is detailed they can often go unnoticed. Sooner or later, though, you may decide there's no alternative but to clean the sensor, and this is a somewhat tricky job that's well within the average photographer's capabilities, but not really for the faint-hearted.

Self timer

2011-05-11T07:33:00.000+01:00

This fires the shutter automatically after a set delay and enables you to get into the picture, or step away from the camera when it's on a tripod so that you don't jog it when you press the shutter release. Most cameras offer a selection of delays, typically 2 seconds or 10 seconds. Some compacts also offer a 'face-detection' self timer which activates when a new face (yours) enters the frame.

Second-curtain flash

2011-05-11T07:31:00.000+01:00

This is a flash mode which can give more realistic light trail effects during slow-sync exposures. Normally, the camera will use 'first-curtain' sync. This means that the flash fires as soon as the shutter opens. The shutter may then stay open to record the ambient lighting. However, this means that an image trail leads forward from the 'frozen' flash-lit image, which can look unrealistic. The movement blur should be behind a moving subject, not in front of it. With second-curtain sync, the flash fires at the end of the exposure, not the start. This means that the 'frozen' image is at the end of the blur trail, not the start, and this looks much more realistic.

SD/SDHC

2011-05-11T07:29:00.000+01:00

SD is now the most popular memory card format amongst compact digital cameras, hybrid cameras and amateur SLRs. The original SD format has now been superseded by SDHC, which offers higher capacities and transfer speeds. There's also an even newer SDXC format designed for cameras and camcorders which shoot high-definition movies, but it's important to check hardware is SDXC-compatible before investing in these cards.

Scene modes

2011-05-11T07:24:00.000+01:00

These are ‘pre-packaged’ sets of camera settings designed for particular situations. The ‘landscape’ mode in a compact digital camera, for example, may set the saturation level to ‘high’, the white balance to ‘daylight’, the sharpness to ‘high’ and the focus to ‘infinity’. Scene modes can improve the quality of snapshots taken by beginners, but most experienced photographers will prefer to choose the camera settings themselves.

Safe shutter speed

2011-05-11T07:22:00.000+01:00

'Safe' shutter speeds are those where camera shake is unlikely. The picture below was shot at too slow a shutter speed, which is why it's blurred. The usual guide to ‘safe’ speeds is to take the equivalent focal length of the lens and divide it into one. For example, a digital compact at its wideangle zoom setting will have an equivalent focal length of 35mm, which means a shutter speed of 1/30sec is likely to be shake-free. It's maximum focal length, though, might be equivalent to 105mm, say, in which case a minimum shutter speed of 1/125sec is advisable. With long telphotos or superzoom lenses, the risk of camera shake increases in proportion to the focal length. With one of the latest 26x superzooms, for example, you may need to use a shutter speed of 1/500sec at the maximum zoom setting (500mm equivalent). Cameras like these, though, have image stabilisers. These keep the image steady in the viewfinder and reduce the effects of camera shake so that slower shutter speeds can be used.

Ring flash

2011-05-10T22:48:00.000+01:00

A specialist flash unit for close-up photography used where the subject is too close to the camera lens for an ordinary flash to work (the lens would obscure the flash). With a ring flash, the flash tube runs in a circle around the outside of the lens and provides an even shadow-less light that's perfect for this kind of photography.

Reflected light reading

2011-05-10T22:46:00.000+01:00

All camera meters use ‘reflected light readings’, measuring the light reflected off the subject to gauge the exposure. It’s straightforward and obvious enough, but it has a major flaw. This method doesn’t distinguish between bright light and objects which are naturally bright in themselves. This is where you need to adjust the exposure manually because no camera can do it for you. It might have the most sophisticated metering system in the world, but it doesn’t have the brain needed to figure out whether objects are instrinsically light or dark in themselves.

Red filter

2011-05-10T22:41:00.000+01:00

This is one of the so-called 'contrast' filters used in black and white photography. Although the pictures are black and white, the film (or sensor) is sensitive to all colours of light, and by blocking certain colours, it's possible to make those colours appear as a darker tone in the photo. Red is the complementary (opposite) colour to blue, so by using a red filter, you block most of the light from a blue sky. As a result, blue skies come out almost black to produce a dramatic, high-contrast image where any clouds stand out vividly.

The pictures above demonstrate the effect. The one on the left shows the original scene in colour, the one in the centre shows it shot as a straightforward black and white photo, while the one on the right has been shot through a red filter. See how dark the blue sky has become? The pale blue hull of the boat has also been darkened, while the smaller red boat further up the beach has become almost white.

It is possible to simulate a red filter using software, for example the Channel Mixer dialog in Photoshop, or Nik Software's Silver Efex Pro. There are technical issues with digital images, though, namely that whatever method you use, the image is created using principally the red photosites on the sensor, which only make up a quarter of the total number. The red channel is one of the 'noisiest', too, so images with a red filter effect applied don't look as smooth as regular black and white shots when examined close up, and may show ghostly halos around objects silhouetted against a blue sky.

Red eye removal

2011-05-10T22:36:00.000+01:00

Red-eye happens because the flash is illuminating the retina at the back of the subject's eye and because the camera lens and the flash are often close together, the lens picks up this red glow through the open iris. What makes it worse is that flash is generally used in dim lighting, when the subject's iris will be wide open anyway.

Camera makers have two ways of getting round this. One is to fire a series of pre-flashes before the main flash. This makes the subject's irises contract, which can reduce the appearance of red-eye. The other is to use a pop-up flash unit so that the flash and the lens are further apart.

Neither methods is 100% successful, so most software applications now include red-eye reduction tools. The smarter applications can analyse images for red-eye and correct it automatically.

Quick AF Live View

2011-05-10T22:25:00.000+01:00

System developed by Sony which allowed some of its SLR models to display a continuous live view. It wasn't done by flipping a mirror up and exposing the sensor in the normal way. Instead, a secondary 'live view' sensor was placed in the camera's pentaprism and activated by a simple switch on the top of the camera. It's a complicated solution, but actually it worked rather well. It now looks, though, as if Sony is dropping this in favour of its more recent 'translucent mirror' design.

Quality setting

2011-05-10T21:57:00.000+01:00

When you save images in the JPEG format in your camera, you have a choice of ‘quality’ settings. This refers to the level of JPEG compression applied. ‘High’ quality images have least compression but the best quality, and also create the biggest files. ‘Standard’ or ‘basic’ quality images are smaller, so you can get more on the memory card, but they’ve been compressed more and you may see a difference in the image quality.

Program shift

2011-05-10T21:56:00.000+01:00

A way of quickly altering the camera’s shutter speed and aperture. In Program AE mode the camera picks the combination of shutter speed and aperture automatically. With program shift you can shift the combinations towards faster shutter speeds or smaller apertures, for example. This gives some of the advantages of aperture-priority or shutter-priority modes without the need to swap to these modes.

Program AE

2011-05-10T21:55:00.000+01:00

This is the simplest kind of automatic exposure mode and it’s found on every digital camera. What the camera does is measure the light level and then choose a combination of shutter speed and lens aperture which will produce the correct exposure.

It’s called ‘program’ AE because the camera takes into account the light level and the zoom setting to choose a shutter speed which will minimise the risk of camera shake, or a lens aperture which offers the best depth of field (near-to-far sharpness), depending on the conditions and according to a preset 'program'.

If you choose one of the camera’s scene modes, it may change the ‘program’ to suit that particular type of subject.

Prime lens

2011-05-10T21:53:00.000+01:00

A lens with a fixed focal length, rather than a zoom. Zoom lenses have taken over because they are more convenient, but prime lenses are more compact and offer better performance, with little or no distortion and, sometimes, better contrast and definition. This is a Nikon 50mm f1.4 prime lens. The maximum aperture of f1.4 is over two stops faster than a typical zoom - one of the advantages of prime lenses.

Predictive autofocus

2011-05-10T21:50:00.000+01:00

A system where the camera tracks the subject as you follow it in the viewfinder, using information from the different focus points to extrapolate the subject’s movement and hence guess where it’s heading. It's a great idea in principle, though many photographers may prefer to pre-focus on a specific position instead.

APS-C sensors

2011-05-10T09:30:00.000+01:00

Digital SLR and hybrid camera sensors come in a number of different sizes, but the most common is the APS-C format. This is about half the area of a full-frame sensor or a 35mm film frame, and gets its name from the APS-C format film cameras that were popular just before the digital revolution. Most amateur and enthusiasts' digital SLRs use the APS-C format, and full-frame sensors are generally reserved for much more expensive professional models. The latest advances in sensors mean that the quality of images from APS-C format cameras can be very high indeed, though these same advances also benefit full-frame sensors, so the gap in quality is still there.

This diagram shows the relative size of APS-C sensors and full-frame sensors. It also illustrates why you have to apply a 'crop factor' or 'focal factor' (1.5x or 1.6x, depending on the exact size of the sensor) when working out focal lengths with APS-C format digital SLRs. For any given lens, they capture a smaller angle of view than a full-frame sensor, which gives the effect of shooting with a longer focal length.

Polarising filter

2011-05-10T08:26:00.000+01:00

Polarising filters cut glare and reflections, and they also darkens blue skies. The effect depends on the angle of the filter - you have to rotate it to find the best position. Polarising filters are popular amongst landscape and advertising photographers, and while you can make blue skies darker in Photoshop, you can't recreate the reduction in glare.

Polarising filters come in two types: linear polarisers and circular polarisers. Linear polarisers are the older, cheaper type, but they can interfere with the autofocus systems in modern cameras, so circular polarisers are the best type to use with digital cameras.

You can get round polarisers which screen directly into the lens's filter thread, or 'square' polarisers which are still round, but slot into square filter holders, such as those made by Cokin.

PictBridge

2011-05-10T08:20:00.000+01:00

A communications standard that allows you to connect any PictBridge-compatible camera to any PictBridge-compatible printer via a USB cable, and to print pictures direct from the camera.

Photosite

2011-05-10T08:19:00.001+01:00

One of the 'pixels' on a digital camera sensor. It's a tiny receptor that measures the amount of light falling on it during the exposure. This is then converted into a digital value by the camera's processor. A single sensor contains millions of photosites, or 'pixels' - hence the term 'mega' (millions) pixels.

Pentaprism

2011-05-10T08:18:00.000+01:00

This is the ‘box’ on top an SLR which reflects the image into the viewfinder eyepiece. When an SLR lens creates the image on the focussing screen inside the camera body, the image is the wrong way round (it’s a characteristic of lenses) and reversed. The pentaprism contains prisms or mirrors ('pentamirror') which make the image the right way round for viewing through the viewfinder.

Panoramas

2011-05-10T08:16:00.000+01:00

A 'panorama' is a super-wideangle photo in narrow ‘letterbox’ shape. Panoramic images have a much wider aspect ratio than conventional shots. They can be taken with special panoramic film cameras (the Hasselblad XPan is one example) or standard digital cameras (by taking a sequence of overlapping shots and ‘stitching’ them together using special panorama-creation software).

The four shots above were taken with a compact digital camera with a 'panoramic' mode. In this mode, the camera shows the edge of the previous image faintly on the LCD so that you can position the next shot so that it overlaps (usually by 20-30%) and the details line up properly.

Some cameras can now stitch panoramas automatically within the camera, some come with special panorama 'stitching' software - programs like Photoshop and Elements can do this too.

Sony has pioneered a new Sweep Panorama mode which shoots all the shots needed for the panorama in a single 'sweeping' movement, and stitches them together in the camera.

Pan and tilt (three way) head

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Tripod head which allows precise camera movement. It can take longer to set the camera position with these than with a ball and socket head, but the adjustment is more precise and you can move the camera along one axis at a time – for example, when ‘panning’ with fast-moving subjects.

Optical zoom

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A lens which offers a range of focal lengths and hence magnifications. On compact cameras the zoom action is controlled by motors and buttons; on a digital SLR, it’s a ring around the lens.

Online lab

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Many companies now offer online printing services. You upload the photos to the online lab, choose the print sizes and numbers you want and pay by credit card. The photos are printed and returned to you by post, usually within just a few days. The uploading process can take a while, and you will need the speed of a broadband connection, but overall it’s still easier than taking your photos to a regular lab and often a good deal cheaper too.

Navipad

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The four-way navigational controller on the back of a digital camera. It’s used for menu navigation, for viewing images in playback mode and adjusting shooting settings in shooting mode. Many newer cameras incorporate a rotating control ring around the outside.

Movie modes

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All compact digital cameras now include a movie mode and the quality is now good enough to rival conventional digital camcorders. Movie modes are ideal for shooting short video 'snapshots' for YouTube or sharing online, but you can also use movie editing software on your computer to assemble clips into professional-looking home movies.

There are two key things to look for:
• Resolution (quoted in pixels)
• Frame rate (quoted in fps)

The minimum for good-quality movies is a resolution of 640 x 480 pixels and a frame rate of 30fps. Almost all compacts meet this standard, but many now offer HD movie modes too. These are usually standard HD (1280 x 720 pixels) but sometimes full HD (1920 x 1080 pixels).

Until recently, digital SLRs couldn't shoot movies. Now, though, as more and more incorporate live view modes, some are also offering HD movie modes too. These offer a big jump in quality, partly because of the increased resolution, partly because digital SLRs have physically larger sensors and partly because of the range of manual controls and interchangeable lenses on offer.

In fact, digital SLRs with HD movie modes can, in many cases, offer a serious alternative to heavy and expensive professional video gear.

Monopod

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A one-legged tripod and more useful than it sounds. Although monopods are obviously not free-standing, they do eliminate movement in at least one axis when you’re shooting. A monopod will also support the weight of a heavy camera/lens, and fatigue in the muscles can be a major cause of camera shake with telephoto lenses. Not as good as a tripod, but much better than no support at all.

Moire

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Interference effect sometimes seen in digital photos. Caused by the way regular patterns in the subject (the weave in a fabric, say), can interact with the rectangular array of pixels in the sensor to produce characteristic elliptical prismatic effects visible at medium to high magnifications. This never happened with film because the distributions of grains in the film emulsion is random.

Mode dial

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The mode dial switches between the camera’s different operating or exposure modes. On a compact camera the dial may let you choose between fully-auto mode, scene modes, movie mode and playback mode (depending on the model, obviously). On a digital SLR it’s used for selecting the different PASM modes (Program AE, Aperture-priority, Shutter-priority, Manual) and, on beginner-orientated cameras, a choice of scene modes. This is the mode dial of a Nikon D50, and many SLRs have similar dials. On a compact, the choice may be simpler, offering full auto, program AE, scene modes and a movie mode, perhaps.

Mirror lock-up

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This is a feature used for shake-free close-ups or sensor cleaning. All digital SLRs have to have a mirror lock-up function so that you can get at the sensor to clean it when necessary. Mirror lock-up is also used in close-up photography – the mirror is locked up several seconds before the exposure is made to allow time for any vibration to dampen down. It’s important to realise these two mirror lock-up functions are unrelated. You need to check that the mirror lock-up feature on a digital SLR can indeed be used for close-up work. Usually this isn’t the case – it’s just there for sensor cleaning.

Midtones

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Tones in the photo mid-way between light and dark. It’s a fairly arbitrary definition that’s open to interpretation, but you might light to consider shadows as the darkest ‘quarter’ of the tones, highlights as the lightest quarter, and the midtones as the rest of the tones in between.

Metadata

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Special text information stored within a digital image. It doesn’t appear as part of the image, but it can be displayed and used by certain image-editing and image-cataloguing applications. EXIF data is one example (the camera model and shooting settings), and IPTC data another (user-editable information such as captions and keywords).

Memory Stick

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Proprietary memory card format developed by Sony and used in almost all Sony digital cameras, though Sony now appears to be making the move towards SD cards, like everybody else. First came the original Memory Stick, which was followed by the faster and larger-capacity Memory Stick Pro. Then Sony developed the Memory Stick Duo, a half-sized version for its compact cameras. The Memory Stick Duo also comes in a Pro version.

Medium format

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Traditionally, 'medium format' cameras were film cameras which used 120 or 220 roll film, so called because the film comes in on a roll rather than in the cassettes used for 35mm film or the single sheets used in large-format cameras.

Pictures were always 60mm high (the width of the roll) but different cameras shot different widths. Some shot square 6 x 6cm images, but there were also 6 x 4.5cm cameras producing shots 45mm wide. Other variants included 6 x 7cm cameras, 6 x 9cm and various wider 'panoramic' formats. The square format was most popular, not least because this gave a lot more freedom when cropping pictures for vertical or horizontal use. The square format has compositional appeal too, although it's rarely used these days.

With the advent of digital imaging, 'medium format' has also come to mean any digital camera with a sensor larger than the 35mm full-frame size. Some are 'full-frame' medium format, in that the sensors match the size of the old 645 format, while others are roughly half way between this and the 35mm full frame size. In any event, the quality improvement over 35mm full-frame sensors is clear and valuable.

There are three main types of medium format digital camera at the moment. The Leica S2 (below) is styled like a super-sized digital SLR, and while it is quite expensive, it's also very compact and straightforward to use for anyone used to a smaller-format camera.

The Pentax 645D is styled like an old-fashioned 645 medium format camera, with a boxy body and a lens mounted on the front. It will be familiar to anyone who's used Pentax's orginal 645 cameras, and the controls and their layout are very similar to those on Pentax's digital SLRs.

Finally, you have 'modular' designs like the Hasselblad digital range (below) and the PhaseOne 645DF. Here, you have a camera body, a lens and a 'digital back'. This is like traditional medium-format film cameras, where you could swap backs according to what film you wanted to use. This is the bulkiest design, but it's also more future-proof in that as sensor design advances you can simply invest in new backs rather than having to buy a whole new camera system.

Macro lens

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A macro lens is one designed specifically for extreme close-ups. All lenses involve optical compromises and only work at their best within a certain range of conditions. Everyday lenses will produce excellent results at normal shooting distances, but when used for extreme close-ups they may show a loss of definition or contrast, distortion or other optical effects which compromise the picture quality. Macro lenses have specialised optical designs to ensure that close-up shots are of the highest quality. They’re usually fixed focal length ‘prime’ lenses rather than zooms, and often have longer than usual focal lengths so that you can keep the camera some distance from the subject.

This Tamron 90mm macro is a digitally updated version of a classic macro lens. It can be used both on full-frame digital SLRs and 35mm film cameras and also on digital SLRs with APS-C sized sensors, where its equivalent focal length is 140mm.

Live view

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Live view is a feature which allows you to compose photos on the LCD display of a digital SLR. This feature is taken for granted on compact digital cameras, where it’s technically simple to feed the image formed on the sensor directly to the LCD on the back of the camera. The optical design of digital SLRs, combined with temperature control problems with the larger sensors has made this impractical with digital SLRs until recently.

However, rapid advances in sensor design, dust-removal systems and autofocus technology mean that live view has quickly become a standard feature on all but the cheapest digital SLRs, and some models even include a swivelling LCD to make it easier to compose shots at awkward angles.

Live view is being used as a big selling point, and it's a feature which will appeal to anyone who's moving up to an SLR from a compact digital camera. However, if you're used to the optical viewfinder of a conventional SLR, you may not find it quite so useful. To many, live view will be more a matter of convenience and familiarity than an everyday essential.

Lithium AA batteries

2011-05-09T20:40:00.000+01:00

These are high-capacity disposable batteries based on similar technology to lithium ion cells, but designed for one-time use only. They are more expensive than alkalines, but their capacity and voltage characteristics make them perform far better in digital cameras. They might cost twice as much as AAs but can last five or ten times longer. They last well in storage, too, so they're ideal for keeping as spares.

Lithium ion battery

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Most compact digital cameras and digital SLRs use rechargeable lithium ion batteries. They’re compact, they store a good amount of power and they can be recharged 500 times or more before they expire.

Lens cleaning

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Does your lens need cleaning? In theory, any foreign body will reduce its performance. In practice, cleaning is best done only when absolutely necessary because the surface of the camera lens can be damaged by overzealous cleaning, and because trying to remove every single speck of dust is a mostly a waste of time.

Ideally, your lens should be perfectly clean (above left), but this is rarely the case. Almost always you'll have a few specks of dust (above centre), but if it's just a handful you shouldn't worry about it. These really won't make a visible difference to the picture quality. Smears and fingerprints are another matter (above right). These reduce definition and contrast to a marked degree. And don't just check the lens's front element - the rear element may also pick up smears and/or drying marks from water splashes or accidental contact with fingertips. In fact, marks on the rear element can have a much bigger impact on picture quality.

But what should you clean your lenses with? Try breathing on the lens and wiping gently with a piece of kitchen roll or toilet roll (tissues often seem to contain oily traces – lanolin maybe – which makes the problem worse, not better). If this doesn't work, try using lens cleaning fluid. Blower brushes are OK up to a point, but the bristles quickly get greasy, and you may remove dust but add smears.

Leaf shutter

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This is a type of shutter built into the camera lens. They’re simpler and cheaper than focal plane shutters, but they're less efficient on interchangeable lens cameras because you're effectively buying a shutter with every lens. They are good for flash synchronisation because they expose the sensor all at once at all shutter speeds.

Large format

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Until recently, this meant a professional studio or landscape cameras which used sheet film measuring 5 x 4" or, in some cases 10" x 8". These cameras are slower to work with but more versatile because the lens and the camera back can be moved and tilted independently. This resolves many perspective and focussing problems which can't be resolved with conventional cameras. in addition, the image quality is breathtaking because of the sheer size of the negative.

The digital equivalent today is the 'digital backs' used in studios. The sensors don't have the same dimensions as sheet film, but they are considerably larger than the full-frame D-SLR size, and offer a big jump in quality.

Kit lens

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Lens bought with a digital SLR as part of a package. Digital SLRs can also be bought in body-only form (without a lens), but for those buying their first camera, and who don't already have lenses, a camera/kit lens package is the most economical choice.

JPEG files

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The usual file format for digital photos and one recognised universally by computers, software and digital devices. The JPEG file format uses what’s called ‘lossy’ compression to produce small, manageable files from digital images. All cameras can save images in the JPEG format, and at different quality (compression) settings.

Infra red

2011-05-09T20:26:00.000+01:00

Infra-red is a part of the spectrum not visible to the naked eye, but visible to certain types of film and digital camera sensors. Indeed, digital cameras have infra-red filters to prevent them recording these wavelengths. However, infra-red light can produce very striking effects. It's normally reproduced using infra-red black and white film and exhibits very strange tonal relationships because the infra-red 'visibility' of different objects is very different to what we're used to. Blue skies are almost black, for example, while foliage is very bright, even white. Kodak's High Speed Infra Red (seen here) is the best-known example of an infra-red film and produces the classic infra-red effect that most photographers strive towards.

This film needed careful handing because the film canisters were not fully infra-red proof (you had to load film in a changing bag), you needed to shoot through a deep red filter to confine the film to the infra-red part of the spectrum, and the focus point was different to visible light, so you had to focus manually using an infra-red focus marker on the lens (only seen on older prime lenses). It repaid the effort, though, with vivid and surreal tonal reproduction, coarse grain and characteristic diffuse, spreading highlights. Konica made a less extreme form of infra-red film which was easier to handle but less striking in its results. It's also possible to get colour 'infra-red', but this simply produces false-colour effects which have a certain novelty value but not much else.

It is possible to recreate the look of infra-red 'digitally', though it's not necessarily easy to produce convincing results because the infra-red component has already been filtered out of the image. Some photographers go to the extent of removing the infra-red filter from the camera, a job that requires the services of a skilled technician and makes the camera unsuitable for normal photography afterwards.

Incident light reading

2011-05-09T20:20:00.000+01:00

This is where you measure the light falling on the subject rather than the light reflected from it (the usual method). It can only be used with separate handheld light meters which have incident light attachments. You stand by the subject and point the meter towards the camera. This is sometimes the only way to obtain a truly accurate light reading.

ICC profile

2011-05-09T20:18:00.001+01:00

Software file which describes a device’s colour characteristics. Photoshop, for example, can use this profile to ‘normalise’ or ‘correct’ the device’s colours to ensure standardised colour reproduction right from the photographed image to the finished print. Many devices come with ICC profiles, while with others you may have to generate them yourself using third-party tools. ICC profiles are not essential for everyday photography, but in professional environments they can provide much-needed predictability.

Cameras don't have ICC profiles, but scanners and printers will need them if they're going to be used as part of a 'colour managed' workflow.

Hyperfocal distance

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This is used to get maximum depth of field in landscapes, where where distant objects (at infinity, basically) are at the far limits of the depth of field. Focussing at the hyperfocal distance ensures maximum sharpness beyond the focus point to infinity, and approximately half way from the focus point towards the camera.

The hyperfocal distance is related directly to depth of field, and is dependent on a number of factors, including the focal length of the lens, the lens aperture and the distance of your subject. It’s gone out of fashion rather, not least because zoom lenses make it impractical to put hyperfocal markers (or depth of field markers) on the lenses in the way that they are on fixed focal length lenses.

Highlights

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Tones at or near maximum brightness. It’s a somewhat arbitrary distinction whose meaning changes according to the context and the user – photographers tend to talk in terms of image tones as ‘shadows’, ‘midtones’ and ‘highlights’, without ever being particularly specific about where one ends and another begins!

Group (lens)

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The individual glass elements within lenses are sometimes designed to complement each other exactly and are cemented together in a ‘group’.

Graduated filter

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Graduated filters are clear at the bottom but darker at the top with a smooth (graduated) blend in the middle. They're mostly used to darken skies in landscape shots. Many outdoor shots are spoiled because there's too big a difference in brightness between the sky and the landscape. If you adjust the exposure so that the landscape comes out well, the sky is overexposed. And if you adjust the exposure so that the sky comes out well, the landscape is underexposed. A graduated filter evens up the brightness so that you capture colour and detail in both the landscape and the sky.

Graduated filters became popular in the days of film but are more important than ever in digital photography. Digital sensors have limited dynamic range, which means that bright skies are often left bleached out with no detail whatsoever. (Even Photoshop can't restore detail which the camera hasn't recorded.)

Graduated filters come in various strengths, usually expressed as a number. A 2x ND filter darkens the image by one stop, a 4x ND filter darkens by two stops and an 8x ND filter darkens by three stops. It does take a bit of experience to gauge what strength of filter you need in any given situation.

Graduated filters slide up and down in the filter holder so that you can get the position exactly right. The filter holders have extra slots which allow the use of two or even three filters in combination. Some makers offer filters with 'hard' or 'soft' transitions to suit the subject.

'Grey' graduated filters are dark grey at the top and produce a straightforward darkening effect, but it's also possible to get coloured grads which tint the sky blue, orange, yellow and so on.

GIF format

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The GIF (Graphic Interchange Format) is a graphics format used on web pages because it produces small image files which download quickly. It can only display 256 colours, though, so while it’s fine for text, logos and simple illustrations, it’s unsuitable for photographs.

Full-frame camera

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A digital camera whose sensor is the same size as 35mm film. The majority of digital SLRs use a sensor that’s smaller than a 35mm film frame and closer to the size of an APS frame (which is why they’re sometimes referred to as ‘APS’ sensors). Full-frame sensors are only found at the professional end of the camera market. At one time, Canon was the only maker to offer full-frame cameras, but they've now been joined by Nikon and Sony. Leica now produces a full-frame digital version of its range finder camera too.

F-stop

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The is an older term for the lens aperture setting. The numbers may appear arbitrary, but they follow a mathematical sequence where each one lets through half the light of the one before. The sequence is (starting with the largest aperture) f1.0, f1.4, f2.0, f2.8, f4.0, f5.6, f8.0, f11, f16, f22. There are intermediate aperture values too. Most zoom lenses only go as ‘wide’ as f3.5. Compact digital camera lenses seldom stop down beyond f8.0.

FPS (frames per second)/frame rate

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How fast a camera can shoot continuously, in ‘frames per second’. A basic digital SLR might be able to shoot at 3 frames per second (fps) while a professional model might manage 8fps or even 10fps. 'Frame rate' is also used to describe the numbers of frames per second in movie footage. In practice, people use ‘frame rate’ and ‘fps’ interchangeably.

Four Thirds

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Four Thirds is sensor and lens system developed by Olympus and Panasonic. The Four Thirds sensor is physically slightly smaller than the APS-C sized sensors in most digital SLRs, but the image quality is similar. The name comes partly from the sensor proportions which are 4:3, like compact digital camera photos. (Digital SLR photos have a ‘wider’ 3:2 aspect ratio.) Olympus claims performance advantages from designing a digital system from the ground up rather than adapting film camera design, and especially the design of ‘digital-only’ lenses better adapted to sensor characteristics.

The body of the E-520 show here is not a whole lot smaller than its rivals, but the kit lens is very compact. And true to Olympus's claims, it does offer very good optical performance.

Focussing screen

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Used to form the image seen in an SLR’s viewfinder. The image passes through the lens, it’s reflected upwards by the mirror and brought to a focus on a ground glass screen mounted horizontally in the pentaprism housing on top of the camera. The pentaprism’s job is to turn the image the right way round and the right way up for when you view it through the viewfinder eyepiece. Some professional-level cameras have interchangeable focussing screens designed for different kinds of photographic work.

Focal plane shutter

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Horizontal or vertical curtains in front of the sensor. Shutters control the exposure. The shutter curtains cover the camera sensor until the shutter is fired. Then the first curtain is released, uncovering the sensor and exposing it to light, and it’s quickly followed by the second curtain, which covers the sensor up again.

Flash sync (x-sync) socket

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Used for connecting an external flash. If your camera has a flash sync (x-sync) socket, you can connect it to studio flash systems. If it doesn’t, you may still be able to buy a flash adaptor from the camera maker which plugs into the accessory shoe on the top of the camera. If that’s not possible either, you can still use studio flash systems by setting them to ‘slave’ mode and using the camera’s built-in flash to trigger them at the moment of exposure.

Flash sync speed

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The maximum shutter speed at which you can use flash. The shutters in digital SLRs are a set of ‘blinds’ or ‘curtains’ which move quickly in front of the sensor to expose it to the image, then cover it again. These move at a fixed maximum speed, and in order to produce higher shutter speeds than this, the blinds (or ‘curtains’) are moved closer together so that the whole frame is no longer exposed in one go, but via a narrow, moving strip. This is no good for flash photography. As a result, there’s a maximum ‘sync’ speed for digital SLRs, which is the maximum shutter speed at which the whole frame can be exposed at once. This is typically around 1/200-1/250sec, but can be higher – on the Nikon D50 and D70s, it’s 1/500sec.

Flare

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An image defect caused by shooting into the light. Flare shows up either as dots or ‘blobs’ of brightness diagonally opposite to the sun in the frame, or as a generally loss of contrast – an over-light ‘washed-out’ effect. If the sun is in the frame, you can’t do much about flare. If it’s outside the frame, a lens hood can reduce or eliminate the flare.

Fisheye lenses

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A fisheye is an extreme wideangle lens that no longer attempts to render straight lines as straight. Instead, they appear as curves which are more pronounced away from the centre of the frame. This distortion effect means that fisheyes are really only suitable for special effects photography, and then only in small doses, though they do have certain scientific/technical uses too (analysing cloud cover for meteorological studies, for example).

Fisheye lenses come in two types: standard and 'circular'. The picture above was shot using a standard fisheye lens. The 10mm focal length offers a very wide angle of view (though no wider than a wideangle zoom) but no correction for curvature, hence the characteristic fisheye perspective. The lens does fill the full sensor area, though.

Circular fisheyes offer the widest angle of view but also the greatest distortion. The name comes from the fact that they don't fill the full sensor area, producing instead a circular image in the centre.

Filters (lens)

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You can attach filters to lenses to modify colours, control the exposure and create special effects. Thanks to the arrival of digital cameras, you can now do many of these things on a computer, of course, but not all of them. There are still some types of filter which are worth using, even with digital cameras, because they do things you can't replicate using software, or because they'd take a lot longer or not come out as well.

Two of the most useful are graduated filters and polarising filters. Graduated filters progressively darken the top of the picture, and they're very useful in landscape photography, where bright skies can often cause problems with exposure. A graduated filter will darken the sky so that it's closer in tone to the landscape. Graduated filters come in different strengths, you can get tinted filters for sunset or blue-sky effects.

Polarising filters darken blue skies and reduce glare off reflective surfaces, increasing the colour saturation. This is an optical effect which you can't reproduce using software. You rotate the filter as you look at the image in the viewfinder or on the camera's LCD display until it looks how you want it to.

Filters come in two forms. You can get round glass filters which screw directly on to the filter thread on the front of the lens. Their advantage is their optical quality and the fact they don't take up much space. Their disadvantage is that they're unsuitable for graduated filters, where you need to be able to move the filter up and down as well as rotate it, and that you have to buy filters to match the thread on the lens. If you have a number of different lenses, you may have to double-up on filters, which means extra expense.

You can also get square filter systems, such as those made by Cokin. These are based on a square filter holder with slots for one, two or three filters at once. You simply slide the filter you need into one of the slots. The filter holder attaches to the lens via an adaptor ring, and if you have lenses with different filter threads, all you have to do is get different-sized adaptor rings for each lens.

The advantage of square filter systems is their versatility and lower cost. Their disadvantages include bulk and, arguably, a slight loss in picture quality since they're made of 'optical plastic' rather than glass.

Filters are designed to work with lenses that have filter threads on the front. That makes them suitable for digital SLR and compact system camera lenses, but not compact digital cameras. These don't have filter threads, though you may be able to get a filter adaptor in some cases. The other alternative is to simply hold the filter over the lens as you shoot.

Fill flash/slow flash

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This is using flash with backlit subjects to lighten the side facing you, which would otherwise be in shadow. It's often used in bright sunlight where the sun is casting ugly shadows. Due to the limited power of built-in flashguns, it only works over a short range – up to a couple of metres. That's plenty for outdoor portraits, though, and it's a popular technique with wedding photographers. You will need to manually activate the flash to make it fire in broad daylight, and you may need to seek out the camera's 'balanced flash' or 'slow sync' mode to get it to balance well with the existing light. It's worked really well here, brightening our subject's face and eyes while still showing the scenery in the background.

File size

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The storage space taken up by the file or its size in megapixels. The file size of a digital image is important because it governs how many shots you can save on your camera’s memory card. JPEG files are smaller than RAW files because they are compressed. The ‘quality’ setting describes the degree of compression, and hence quality loss. The best compromise between file size and overall image quality is to set the camera to its maximum image size/resolution, then choose the ‘Normal’ rather than the ‘High’ quality setting.

File formats

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Digital cameras save images in the JPEG format or, with more advanced models, a RAW file format that preserves the full image data for conversion later on.

Some models can also produce TIFF files, which are larger than JPEGs because they’re not compressed. TIFF files, technically, offer higher quality as a result, but the differences can be negligible, while the costs (in terms of increased file size) are high. The TIFF format is no longer common on digital cameras. It can be useful on your computer, though, where outright file size is no longer a problem. The Photoshop file format may prove the most useful, though, because this does not sacrifice image quality with compression and it preserves all the layers, masks you create during your editing work. Most photographers shoot JPEGs, which they then save as Photoshop files where editing work’s been carried out, or shoot RAW files, convert them to TIFFs, then save them as Photoshop files when they’ve been worked on.

Exposure latitude

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This is the ability of the camera (or its sensor) to cope with over- or under-exposure. Digital cameras seldom have a great deal of exposure latitude because even slight overexposure can cause ‘blown’ highlights which have lost all detail. Digital cameras do have more underexposure latitude, though, and it’s often possible to get usable images from very dark-looking originals. The term 'exposure latitude' was used widely in the days of film but isn't used so much these days, and digital photographers tend to talk in terms of 'dynamic range' instead.

Expeed (Nikon)

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'Expeed' is the name Nikon gives to the image processing system inside its top-end cameras. This looks after the conversion of the data captured by the sensor into the image files saved on the memory card. Improvements to the image processing system have an impact on the speed and performance of the camera.

Element (lens)

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Modern lenses have many glass elements. Lens elements are individual glass lenses cemented together in groups. Many lenses are needed to provide zooming, focussing and close-up functions while correcting all the optical aberrations that a single lens would have.

Edge effect

2011-05-09T07:33:00.001+01:00

Visible ‘halo’ around the edges of objects in photos usually caused by sharpening. Sharpening, whether it’s applied in-camera or in your image-editor, works by increasing the contrast around the edges in your image. This produces edge ‘halos’ or secondary outlines. These will become visible if you over-sharpen the image. All image sharpening is a trade-off between increased sharpness and edge effects (or increased noise).

DPI (dots per inch)

2011-05-09T07:31:00.001+01:00

Dots per inch, a measure of resolution in prints and scans. How many pixels (or ‘dots’ - the two are now commonly regarded as the same thing) are printed per inch. It’s also used by printer makers, though a printer’s ‘dpi’ quoted in the specifications is a different thing, referring to the number of dots of ink per inch squirted on to the paper. (Many dots must combine to produce a pixel.)

D-Lighting (Nikon)

2011-05-09T07:29:00.001+01:00

This is a technology developed by Nikon for lightening dark shadows in photos. D-Lighting is a software process which lightens the shadows but leaves the midtones and highlights unaffected. Nikon’s D-Lighting can be applied to images already saved on the camera’s memory card, or using the Nikon software that comes with the camera on the computer.

D-Lighting works well enough, but it can only enhance dark shadows. 'Blown' or 'overexposed' highlights are generally more of a problem, and there's nothing it can do about these.

This is why Nikon has now developed 'Active D-Lighting'. In this mode, the camera adjusts the exposure before it takes the picture so that the highlights aren't overexposed. Then it applies the D-Lighting process as the image is saved.

This gives better results, but it does mean you're committed to the D-Lighting process because the camera exposure is changed with this in mind.

Distortion

2011-05-09T07:28:00.000+01:00

Distortion is where straight lines become curves or appear to converge, and it comes in two types: perspective distortion and lens distortion. Perspective distortion is natural and inevitable. It’s when the tops of tall buildings appear to converge or railway lines converge to a point in the distance. This is not a lens defect, it's just a by-product of where you're standing, how the camera is tilted and the lens's angle of view. However, zoom lenses tend to introduce an additional and different kind of distortion. At wideangle settings, straight lines at the edges of the frame appear to bow outwards (‘barrel’ distortion) while at the maximum telephoto setting, lines appear to bow inwards (‘pincushion’ distortion).

This picture shows both perspective and lens distortion. Because the camera had to be tilted upwards to get the full height of the pier pavilion in the frame, this has introduced perspective distortion, where the walls appear to converge towards the top. However, if you look closely, you'll see that the sides of the pavilion are also curved, and to quite a marked degree in fact. This is barrel distortion, a largely unavoidable property of zoom lenses at their minimum (wideangle) focal length. This often swaps over to pincushion distortion at the maximum focal length. With pincushion distortion, these walls would bow inwards rather than outwards.

DIGIC

2011-05-09T07:24:00.000+01:00

This is the name of Canon's in-camera processing system. It handles the conversion of the data captured by the sensor into the image files saved on the camera's memory card and various other internal camera functions. Every camera maker has an equivalent system for its cameras. Improvements to the image processing system are often used as a selling point for new cameras, since they do have an impact on the camera's usability, performance and image quality.

Diffraction

2011-05-09T07:19:00.001+01:00

Optical effect which limits lens quality at small apertures. Light bends (diffracts) as it passes through small gaps. The smaller the lens aperture, the smaller the gap, and the greater the proportion of light ‘bent’ at the edges. This has an overall softening effect, and you can start to see definition falling away with digital SLR images at apertures of F11 or lower. On a compact, because the lenses and apertures are tiny, diffraction effects may be visible at apertures of f5.6 or f8.

Demosaicing

2011-05-08T21:47:00.000+01:00

Digital camera sensors use grids of red, green and blue pixels. Each pixel can only record red, green or blue light. Each pixel produces a single block of colour and, as a result, the image at this point looks like a mosaic, not a photo. The camera’s processor has to interpolate or mathematically ‘guess’ the extra colour information from the surrounding pixels. Because it’s getting rid of this ‘mosaic’ effect, the process is called ‘demosaicing’.

If you shoot RAW files, the sensor data is captured before it's been demosaiced, and the demosaicing process is carried out by the RAW software instead. Different RAW conversion programs use different demosaicing processes, which is one of the reason why the results you get will vary from one program to another.

Continuous Shutter (CS)

2011-05-08T21:43:00.000+01:00

A high-speed shooting system developed by Casio and used in a number of its compact cameras. It allows short-burst continuous shooting at 30 frames per second or more, and high-speed movies which can capture fast-moving subjects and play them back in slow motion.