Very broadly, the middle brightness tones in a photo. Imagine the full range of tones in an image split into four equal parts – the darkest quarter makes up the ‘shadows’, the lightest quarter makes up the ‘highlights’ and in between are the ‘midtones’.
Where you set both the shutter speed and the lens aperture used by the camera. The camera’s exposure meter may recommend the settings, but you’re free to use or ignore this information. Manual exposure gives you total control but requires some experience.
A photo where most of the tones are dark, such as a black cat in a coal cellar. You can also give photos a low key look with slight underexposure. It gives photos a dramatic, moody look, though the subject matter has to be right for this to work properly.
Long exposures turn moving subjects like water and clouds into an atmospheric blur. The exposure time often needs to be several seconds or longer, so a tripod is essential. In bright light you’ll need a neutral density (ND) filter to get these long exposures.
A device for measuring light levels. Digital cameras come with their own sophisticated internal light meters, but it is possible to get external light meters where the settings have to be transferred to the camera manually. This is slower, but has advantages in some circumstances.
A graphical display of the brightness values in the picture. The darkest tones are at the left and the brightest on the right, and the vertical bars show the number of pixels for each brightness value. Histograms are an invaluable exposure aid when taking pictures, and when editing them later.
When you shoot RAW files there is often a little extra highlight detail in the data than is initially visible, and a good RAW converter will be able to recover this detail to correct any ‘blown out’ areas. There’s no much margin for correction, however – typically you might be able to recover 1EV of additional highlight detail, but rarely more.
The lightest tones in a picture. It’s a pretty vague definition, but most photographers take it to mean tones which are at or near a full, featureless white. Retaining or recovering highlight detail – in bright skies, for example – is a big priority for keen photographers.
A photo where the tones are predominantly bright or white. It’s partly the subject that makes a photographer high key – a white cat on a white cushion, for example, and partly the exposure technique – slight overexposure will give a high key look.
Used for accurate white balance calibration, usually under artificial lighting where the colour of the light sources is unknown or variable. You can use the camera’s manual white balance preset control to take reading from the grey card, or set the white balance using the card and the WB eyedropper tool in many image-editing programs.
Flash power is usually handled automatically by in-built flashguns and external flashguns. The exception is studio flash, where you adjust the power manually in fractions of full power. 1/1 is full power, 1/2 is half power, 1/4 is quarter power and so on. Some smaller flashguns offer manual power settings too.