As soon as you press the shutter release on your camera, very complex calculation processe takes place in it that determines how the image can best be exposed. In fully automatic mode, the camera uses these calculations to decide on the choice of aperture , shutter speed and ISO value and thus has a considerable influence on the composition of the image. But even if you work, for example, in the aperture preselection mode with a fixed ISO value, the camera still diligently calculates what it believes is the optimal exposure and selects the appropriate shutter speed, and the appropriate aperture value for the preset time.
Measurement Methods Of The Camera
The camera’s exposure measurements have been extremely sophisticated over the years. But even the best technology cannot always calculate the optimal exposure or the most appropriate exposure for the subject without errors. For this reason, you can choose different exposure modes on the camera for different picture and exposure situations.
On the basis of this choice, one basically decides which portion of the image the camera should include in its exposure measurement. Multi-field metering, integral or center-weighted metering, selective metering and spot metering are usually available. The order in which they are listed goes from the least to the most selective measurement mode.
While the multiple field measurement includes almost the entire image in the measurement, the camera only concentrates on the center of the image with the integral measurement and ignores the rest of the image. The selective measurement only takes into account a small part of the center of the image and the spot measurement only takes one pixel into account.
Application Of The Measurement Methods
The different methods of measurement can be beneficial for a wide variety of lighting situations. In many cases, multiple field metering is usually the best option. Though the multiple field metering option has some limitations especially with evenly lit image situations, and also in a situation where you have very high-contrast. Also it becomes challenging if your main object is in the shadow; very dark and can be seen against a light background. Evaluating the metering in this case becomes problematic. What the camera does in cases like this is that it outweighs the light areas against the dark areas, which can result in the main dark subject being underexposed in the photo. In cases like these, it is better to use integral or selective measurement. The two sample images illustrate the enormous differences that can arise from different measurement modes.
Another very simple method of correcting possible incorrect calculations by the camera is exposure compensation . With this you can correct the incorrect exposure of the multiple field metering in the above example image in another way. Instead of changing the measuring mode right away, you simply tell the camera: “The picture is too dark for me, please expose it more intensely” You can do this with the help of the exposure correction, which you can set with fixed light values (usually specified in 1 / 3EV steps) adjust up or down. Settings in the minus area tell the camera: “The picture is too bright , make it darker” While settings in the plus area result in a brighter image . The latter choice would be applied to the example image above, among other things.
How far you should regulate the settings in the plus or minus range depends on the exposure situation. The more contrasting and extreme the differences in light in the image, the more intensely you can or even have to intervene in the camera’s automatic exposure.
But also, low-contrast, or consistently very bright or very dark images often cause problems for the automatic camera. Example of this is a black image in front of a dark background, which will in most cases interpret the camera’s exposure as too dark and will want to expose accordingly more intensely. But unfortunately this causes overexposure of the picture. If you do not adjust the settings in the minus area by means of exposure correction, the picture would be too light / gray. Similarly, consistently bright images without exposure correction in the plus area would be underexposed / too dark.
In order to be able to understand these processes better, you should simply try out the discussed measuring methods with different exposure situations. With this way you will quickly get a feeling for the situation in which you can use the correction and how much, or whether you should use a different measuring method.