Exposure metering is the collection of data by the camera about the level of illumination in the frame. In modern cameras, it has different modes of operation to determine the correct exposure and is used depending on the lighting conditions.
In the early stages of the development of photographic technology, in cameras, the exposure parameters were set by the photographer based on the readings of a selenium exposure meter built into the camera, or an external selenium exposure meter, which used the entire area of the light window to measure. With the widespread introduction of advanced metering sensors into cameras, initially exposure metering was produced in almost the same way, and the parameters were set according to the "average temperature in the hospital".
Over time, with the development of technology, others have been added to the average measurement. In this article, we'll take a look at the types of metering available in modern cameras.
English Average metering — as mentioned above, with averaged metering, the sensors register the brightness of the illumination over the entire area of the frame window, and then the average indicator is calculated programmatically, and the exposure is set according to it.
The exposure metering method is good in the case of photographing a scene with low contrast, when all objects are illuminated evenly, and it is very often mistaken in situations with very sharp transitions of brightness between the subject and the background. That is, when shooting, in which, for example, the earth and a bright sky participate, it will not be possible to get the correct exposure - one of the zones will be overexposed.
English center-weighted Metering, Center-weighted Average Metering — almost all manufacturers have the same implementation. When using this mode, metering is carried out in the center of the frame, with a smooth transition to the edges. For the first time, such a mode was implemented in a Nikon F camera, with the central part occupying about half of the light-sensitive area of the exposure meter.
This approach made it possible to more accurately measure the level of illumination of objects, and coped well with shooting portraits in difficult conditions, as well as sequential shooting, before the appearance of evaluative metering.
Evaluative, matrix, multi-zone metering
English matrix metering, Evaluative Metering, Multi-pattern Metering - is based on dividing the area of the frame window into several parts, the data from which are taken simultaneously, and the camera electronics sets the exposure parameters based on the data previously entered by the manufacturer. First appeared on the Nikon FA in 1983, where the frame window was divided into five metering zones.
Nowadays, it is the main one for most digital cameras, and the measurement zones have become much larger (32 for the Canon-1Ds camera of 2004 and 252 for modern flagships such as 1D X, 7D mark II of 2012 and 2014), moreover, the ability to select the main point has been added metering together with the focusing point, and in professional models and the ability to measure the flux density of red, green and blue. In the most sophisticated metering sensors, not only the illumination of the zones is taken into account, but also the color of the image, the distance to the object and the volume of the scene, there is a face recognition algorithm.
For the first time a sophisticated metering algorithm was implemented by Nikon in the Nikon F5. This type of exposure metering is quite versatile when shooting on an automatic machine, but gives completely unpredictable results on a semiautomatic device. In film photography, the type of multi-zone exposure metering was realized by a group of lenses located in front of the photoresistor of the exposure meter or a photosensitive matrix.
Spot, sophisticated spot metering
English Spot-Metering, Fine-Spot Metering - in this mode, exposure metering is performed by the central part in the frame, but having an area of one to seven percent of the entire area of the frame. Typically, the metering area is marked in the center of the viewfinder. In this case, information outside the measurement zone is cut off. Many cameras have a multi-zone spot metering mechanism.
The metering results are memorized by the camera and, based on them, the average value of the required exposure is displayed. For example, we alternately fix the exposure with a button on the camera body in highlights, shadows and areas of medium illumination - the camera calculates the average exposure value. Refined spot metering captures an area even smaller than spot metering (1-2%). Excellent for shooting static objects, and inferior to matrix in efficiency.
English Partial Metering - covers a slightly larger area than is used in spot metering - usually about 12-15 percent in the center of the frame. As a separate mode is available in Canon cameras, in models of some other manufacturers it is set by increasing the sensitivity area of spot metering. For the first time, spot metering was implemented in a Pentax Spotmatic SLR camera; before this camera, only external exposure meters had the ability to meter using a narrow angle. Unlike evaluative metering, partial metering Convenient when the background is much brighter than the subject due to backlighting (backlighting).
What metering should I use?
There is no way to draw a conclusion here - everything depends on the experience and taste of the photographer, and also depends on the current shooting conditions. If you are a beginner and it is a little unclear for you how to work with all modes, set matrix or evaluative metering in the camera parameters. It is suitable for most situations - including reportage shooting.
Spot, partial metering can be used when shooting static scenes with some experience. In reportage shooting, using them promptly is quite problematic, although it is not forbidden. Using manual editing of exposure parameters will help you get photos that are much better than those that you see when shooting on the machine.
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