Hot Spot
Areas in an image where the sensor has reached the maximum amount of brightness it can register. These areas lose contrast and appear white.
JPEG
An image compression method. The amount of image compression can usually be varied in the camera or when saving files on your PC. A higher JPEG compression factor will result in a given file having a smaller size, thus aiding storage but the compression will result in flaws in the image which may be visible when viewed.
Multi-segment metering
In this form of exposure metering, the camera takes measurements from a range of different points in the image and evaluates all the different light meter readings. It will then choose camera settings to give what it thinks is the best compromise for the correct exposure over the whole image.
Noise
Image roughness or unevenness, usually visible as areas of faint random colours seen against the intended background colour. Often caused by particularly low shutter speeds. Compact cameras and “superzoom” model cameras will suffer from noise more than dSLR models as compact/superzoom models have more pixels crammed into a smaller area on the sensor. This higher density of pixels causes interference between the adjacent pixels and is often the source of noise.
Prime Lens
A lens with a fixed focal length. Usually “faster”, i.e. capable of a wider maximum aperture, than a zoom lens set to the same focal length. Almost invariably capable of better optical resolution than a zoom lens set to the same focal length. Lacks the flexibility of a zoom lens.
Program Mode
A mode of operation where the camera automatically selects both the shutter speed of the camera and the aperture of the lens to give what it thinks is the correct exposure. Sometimes referred to as “Point and Shoot”.
RAW data
Unedited image data output from the camera’s sensor. Raw data is data before it has been internally processed by the camera. In addition, RAW data is 12bit data that contains 16 times the information of 8bit JPEG and TIFF data. It is possible to correct bigger errors in exposure or white balance if the RAW data is available to be worked on. RAW data needs processing using the software provided by the camera manufacturer or a third-party application such as Adobe Camera Raw before it can be viewed by standard picture viewing applications.
Sensitivity
Usually measured as an ISO “film speed” value typically between 50 and 3200. Each doubling of the number, e.g. from 200 to 400, doubles the sensitivity meaning that half the amount of light is needed to obtain the correct exposure. With a high sensitivity. images can be shot with a high shutter speed even in dark places, this can be used to reduce camera shake. However, images with high sensitivity are more susceptible to noise.
Shutter Priority
A mode of operation where the photographer has control over the shutter speed of the camera. The photographer manually selects the shutter speed and the camera then automatically sets an appropriate aperture to give the correct exposure. This is most often used when the photographer wishes to control the amount of motion blur in the resulting picture. Motion blur can be unintentional due to camera shake, or intentional to convey a sense of movement. A faster shutter speed will have a greater tendency to freeze the motion of the subject, i.e. reduced motion blur.
Shutter Speed
Measured in seconds, it is the length of time that the shutter is open and allowing light through to the sensor. Altering the shutter speed changes the amount of light that strikes the sensor. The shutter speed is proportional to the amount of light allowed through to the sensor, i.e. doubling the shutter speed from 1/125th of a second to 1/250th of a second halves the amount of light the sensor receives.
Spot Metering
A light metering mode where the reading is taken from a very small “spot”, usually in the centre of the image. Usually spot metering is done so that the spot metering point is the part of the image the photographer wants to be correctly exposed and there are other areas in the image that would otherwise confuse the metering. Exposure Compensation may still need to be applied.
sRGB (standard RGB)
International standard of colour space established by the lEC (International Electrotechnical Commission) This is defined from the colour space reproducible on PC monitors and is also used as the standard colour space for Exif.
Vignetting
Usually refers to darkened corners on an image. Vignetting can occur when a flashgun has not been set to a wide enough angle to cover the image in view. Vignetting can also occur if a lens designed for a digital sensor is used on a film camera body (see Crop Factor).
White Balance
The colour temperature and tint of an image is adjusted to match the light source so that the subject appears be the correct colour. This is known as setting the White Balance point, you are defining what is “white” for a given light source. A range of typical White Balance settings on a camera could be daylight, shade, cloudy, fluorescent light, tungsten light or flash.
Zoom Lens
A lens which can be adjusted over a range of focal lengths. Usually “slower”, i.e. not so capable of a wide maximum aperture, than a prime lens of the same focal length. A compromise on optical resolution compared to a prime lens. Has flexibility as one lens can be used in place of a range of different prime lens.
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