K (Kelvin)

Thermodynamic temperature scale measurement. In 1933, the International Committee of Weights and Measures adopted the temperature at which water, ice, and water vapor coexist in equilibrium as a fixed point, the "triple point of water"; its value was set as 273.16. The unit of temperature on this scale is called the Kelvin, after William Thompson Lord Kelvin, and its symbol is K (no degree symbol used). In photography it is used to measure the color temperature of light at different wavelengths.

Key Light

When lighting a photographic subject, the main light source.

Keystoning

Distortion of a projected image when the projector is not directed perpendicular to the screen. Also applied to the convergence of vertical lines in tall buildings when not photographed with a Perspective Control (PC) lens.