Glossary "R"

Computer memory that is used to run the computer’s operating system and software programs. The software program indicates how much memory is needed to run it on the box or in its instruction leaflet. This figure is on top of what’s needed to run the operating system.

An optical device that’s either built into older cameras or added as an attachment that is used to work out the subject distance by comparing two viewpoints. You see a double image and adjust the lenses until the images form one which gives a distance reading that can then be transferred to the focusing ring.

A fast fixing bath that includes ammonium thiosulphate or thiocyanate.

A picture file format that some of the more advanced cameras have the option of using when taking photographs. In this mode the photograph is captured in a "raw"state direct from the camera's CCD so no automated processing is done by the camera. You then use RAW processing software such as Capture One to view and process the file on your computer giving you complete control of properties such as exposure, colour and sharpness. This mode is preferred by enthusiast and professional photographers who tailor settings to there liking. The downside is the file is not compressed by the camera, like it is in normal jpg shooting mode so you can only shoot a small number of photos before the memory card fills up.

Printing paper that has a plastic, or resin coated, surface to speed up processing and offer a high gloss finish.

Unlike resampling here the image size is changed without modifying the resolution. For example if you resized a 10x8in 72dpi photo to 4x6in the dpi would be increased, whereas if you resample youd keep the same dpi.

The unexposed areas surrounding the images recorded on film.

Reciprocity law states that as you increase the intensity of light reaching the film you also need to decrease the speed it reaches the film by the equivalent amount. Most films work quite happily between exposures of 1/2sec and 1/1000sec, but go beyond these extremes with a very low intensity of light and a long exposure or a very high intensity of light and a correspondingly short exposure and the law fails an exposure increase may be required when the shutter speed is beyond these limits. At these extremes the law fails. Compensation is required to adjust for this, but there is no strict rule to correct the error. Most film and paper manufacturers provide technical details on request with a rough guide to exposure adjustments. As a rough guide for an exposure of one second you would increase the speed to two seconds, or open the aperture by one stop. A speed of 10sec would need to be increased to about 50sec or open the aperture up two stops. With black & white film you only have to worry about this exposure correction, but with colour film does not only suffer from exposure problems but also colour casts. A colour film is made up of three individual colour layers, each layer suffers from reciprocity failure at different levels. On an uncorrected film the shadows may have a magenta colour cast but the highlights may suffer from a cyan cast. To correct the cast not only would a longer exposure be needed but also the inclusion of a colour correction filter of a low value, care would have to be taken in choosing the correct filter otherwise an over corrected result may appear.

To make an exposure, a photographer can, for example, choose a combination of a small aperture and a slow shutter speed or a large aperture and a fast shutter speed. Each movement of the aperture is classed as one stop – go from f/8 to f/11 and you close the aperture by one stop. Similarly by adjusting the shutter speed from 1/125sec to 1/500sec you reduce the exposure by one stop. If you adjust the aperture by a stop and counteract this by also adjusting the shutter speed by one stop you will produce the same exposure value. Therefore an exposure of f/8 at 1/60th could be changed to any of the following combinations: f/11 at 1/30th, f/16 at 1/15th, f/5.6 at 1/125th or f/4 at 1/250th. This is called the law of reciprocity (if one value increases the other will decrease proportionally and visa versa).

An ultrawide-angle lens with a focal length of around 15mm that has been designed to reproduce straight lines with little distortion.

The time it takes for an electronic flash to fully recharge. Automatic thyristor flashguns have special circuits that store unused flash ready for the next shot so recycling speeds up. This is essential for fashion and sports photography, but less so for still life. The recycling time of more powerful or manual units is usually longer.

If you've ever taken a photo in low light using a compact camera or an SLR with built-in flash you will have no doubt come across a strange effect - people with alien-looking eyes. The reason is simple; the flash lights up all the blood vessels in the eye which reflect back into the lens. The further away the flash is from the lens the less likely the chances of this strange phenomena occurring. The problem with built-in flash is that you can't control where the flash fires from. To overcome this, many cameras have a red-eye reduction mode, but it is, as the name suggests, only a reducer. It works by firing a pre flash to reduce the size of the pupils, and in doing so reduces the area of red. The redness is still usually apparent, but because the pupil is smaller the effect is less noticeable. There are three methods used in cameras to reduce red-eye. One is a single pre flash. This is quite bright and can fool the subject into thinking the picture has been taken. So you avoid red-eye but have a picture of a person either looking away or blinking. The second method fires a less powerful, but equally distracting, sequence of flashes, almost like a strobe. This can result in the unaware person shielding their eyes from the potential epilepsy inducing strobe! Version three tends to be the most subtle - a torch-like light that shines for about five seconds before the flash is taken. The only downside of this is battery drain. If you have a computer you can remove red-eye digitally using image editing software. If you don't there are special pens available that you can use to colour in the red on your photos.

A chemical thats used to reduce the density of a processed negative, often referred to as Farmers Reducer.

An exposure reading that measure from the camera position with the metering sensor pointing towards the subject. This is the system used by most through-the-lens systems or with handheld meters that haven't got an invercone over the sensor. The angle in degrees is usually quoted.

When light rays change path as they pass through one transparent object, such as a lens element, to the next.

Indicates how good binoculars are in low light. To find this divide the objective lens by the magnification and square the result. A 10x40 has a relative brightness of 16 (40/10= 4, 4x4=16). A higher number means the binoculars will be better in low light situations.

A control panel that is either connected via a cable or using infrared. A simple one allows the slides to be changed forwards or backwards and the focus to be controlled. More advanced ones have built-in light pointers and slide preview window.

A portable hard drive such as a Zip drive or Magneto Optical that uses removable cartridges to hold data. Zip disks are either 100 or 250Mb while magneto optical are 230Mb, 640Mb or 1.3Gb. The disks can be reused and are ideal for backing up and transporting large digital images.

Memory cards such as CompactFlash, SmartMedia or MemoryStick that are used in digital cameras to store images.

A solution used to top up and maintain part used processing chemicals. This is more economical because you can extend the life of previously used stock by replacing a measure of it.

Another name for interpolation where pixels are added or removed to change the physical size of the image.

The camera's light sensitive CCD converts the scene into a grid of pixels that make up a digital photograph. The resolution is the total number of pixels in the photo, for example, one million or 350,000. This is one factor that affects image quality, providing the image that's being formed on the CCD is sharp. CCDs with greater numbers of pixels should have higher resolution. Buying adviceUnless you have a specific need for a low resolution model choose a camera with the highest resolution you can afford. This will enable you to make bigger enlargements.

Also known as a reverse or inverted telephoto, this lens design has a diverging lens element positioned in front of the aperture and a converging element positioned at the rear. This makes the distance from the rear of the lens to the focal plane longer than the lens focal length. Retrofocus design has been adopted in wide-angle lenses so the rear of the lens does not impede the movement of an SLR camera's reflex mirror.

A film to produces transparencies that are viewed with projected light.

The three additive colours that mixed in digital imaging to create the large range of colours. Overlapping these colours in varying strengths creates cyan, yellow and magenta while equal proportions creates white. Computer monitors create accurate colour by firing light through red green and blue phosphors while digital cameras and scanners use RGB filters over the CCDs to create the colour information.

A flashgun that has a circular electronic tube that is positioned around the camera lens or on the filter thread. It’s used in macro photography to produce an even distribution of light while fashion and still-life photographers create interesting halo shadows around the subject.

Software used by high-end postscript printers that prepares the file to be printed by converting vector images into a bitmaps.

A control found mostly on large format cameras that allows the lens to be raised parallel to the film plane. Its used in architectural photography to ensure the verticals of buildings stay straight when shooting with wide angles from low viewpoints.

An adaptor that fits onto the back of a large format camera to allow roll-film to be used back. Also used on many medium format cameras to allow film to be changed mid-roll.

A rolling shutter exposes different portions of the frame at different points in time, “rolling” through the frame.

Used in many CMOS sensors, exhibiting skew, wobble, and partial exposure.

Digital memory used in computers that cannot be overwritten. Many of the basic operating system controls are factory installed in the ROM and cannot be accidentally erased.

Design of binocular prisms that allow straight tubed body used by many of the slim pocket style models. The other is porro prism that has prisms arranged at 90 degrees, giving a step shaped, and more bulky, design.