When you look at camera exposure it can be complex or very simple. If you let your digital camera do all the work then it is quite simple. The issue arises when we want to improve on automatic settings.
Sun light is invisible to us.When sun rays shine on an object they are divided in two groups. Some rays are absorbed by the object which causes the inner temperature of that object to increase. The rest of sun rays get reflected, this is the visible light.
Example: Imagine you are sunbathing on a beach and feel warm and sweaty. This means some of the sun rays are absorbed by your body. If you look at some other person on the beach covered with sunscreen it is hard to look at this person without sunglasses since a sunscreen intensifies sun reflection.
Very reflective objects are white like snow or bright yellow like gold. Dark colored objects absorb most of the sun light and reflect very little. I wear dark colored cloths in winter to absorb as much heat as possible.
When sun light is intense the difference in brightness of different objects is so big that a camera cannot record detail on all surfaces. The consequence of this are some parts of the image being white or black without texture or detail.
Example: Imagine photographing a person sunbathing on a beach when sun is intense. A camera can capture nicely either person’s body or the background. In the first case the person’s body is rendered nicely with the sand and water rendered white with no texture. On the other hand the exposure can be adjusted to render sand and water nicely with the person’s body dark without much texture. See the image below:
Since camera cannot record all the detail in bright conditions some trade off has to be made. The first approach is to measure light on numerous places throughout the image and find the mean. The resulting image will have most of the image properly exposed with some white and black spots without detail. The second approach is to expose the image for what is most important. Only the object of our interest will be properly exposed with the rest of the image white or black without much detail.
In camera language the first approach is called “matrix metering”. In the second case it is “spot metering”.
What is better to use matrix metering or spot metering?
There is no definite answer. It depends on personal preferences.
Example: When I photograph an event with people I optimize exposure for faces of the people. I believe my images will be judged by people faces first and then everything else. The background may not be exposed perfectly but will be recognizable.
Some people think differently. They expose to optimize exposure for most of the detail on the image and if a face is not rendered properly they will tweak it in post processing. So they want to show the environment where the image is taken.
The image below shows the dilemma:
At the end of the day, it is about personal preferences. My camera is set to spot metering all the time. I encourage you to try both settings and see what works better for you.
Exposure can be improved by some other remedies such as:
Furthermore some cameras are more forgiving than the others. As well as post processing can impact the result.