Object measurement
The object measurement is a term used in photographic technology and describes a specific method of metering . It is the direct opposite of light measurement .
Approach and technique
In the object measuring the aiming photographer with its external or in the camera built-in light meter the photographing motif (thereof, or certain parts) to the at light value for the reflected object light to be determined.
The object measurement is divided on cameras with built-in light meter in three different ways:
- Spot exposure metering ( spot metering )
- Integral measurement
- Matrix measurement or multiple field measurement
In the case of handheld exposure meters, there are high-quality models for integral metering that can also be used for spot metering and light metering. There are also specialized spot light meters . When measuring objects, the light is always measured from the position of the camera in the direction of the subject.
Advantages and disadvantages
While light measurement - especially when taking pictures in the great outdoors - is often not possible due to the distance to the subject, object measurement can always be carried out. The exposure meters built into the camera can also take into account the technical and optical conditions of the camera, lens and optional flash unit. For example, the active autofocus point can be assigned a different weighting during the measurement or the flash can be switched off as soon as enough light has fallen on the film or sensor.
However, the object measurement leads to incorrect exposures if the subject deviates from the assumed “correct” average brightness of 18% gray, because the light reflected to the camera and thus the measurement result depends on the degree of reflection of the subject. For example, if a polar bear is photographed in the snow during twilight, it may reflect just as much light to the camera as a black cat on a pile of coal at lunchtime. The object measurement will expose the film or sensor equally in both cases, namely in such a way that the brightness of the image corresponds to that of 18% gray. Polar bears and cats will both be shown in gray instead of white or black.
The light measurement, on the other hand, measures the light incident on the object without considering the subject. So it would correctly recognize with the polar bear that there is twilight and suggest a higher exposure than with the cat in the bright midday sun. The bear is shown in white, the cat in black.