What is the metering of SLR cameras? What's the use? How to use it?

Photometry, as its name implies, is to measure the light intensity within the range of framing.

It's like measuring altitude.

The ultimate goal of photometry is to provide exposure reference for our shooting. To put it simply: if we look at a photo and feel black and gray, it is probably because of underexposure; If it looks too bright and white, it is probably due to overexposure.

In actual shooting, three photometry methods are mainly used:

1. Spot metering: only one point within the framing range (less than 5% of the whole range) is metered.

2. Key metering: metering a key area within the framing range (within 15% of the whole range).

3. Area (or evaluation) photometry: This is to divide the whole shooting range into many areas, then measure the light separately, and finally work out a compromise result.

In photography, photometry is one of the most important three elements (photometry, focusing and composition), and it is also the most difficult element to master.

The main reason is that (all) cameras are very poor in light resistance (much worse than human eyes), and usually the light resistance of nature is very large, so it is necessary to determine the choice of exposure through photometry.

For example, all cameras are like clothes of size XS, which are very small. But after all, we normal people seldom wear XS size, and most of us have to wear clothes in large sizes such as S, M, L and XL. But the camera is so small, what should I do? We can only make a choice by measuring the light, either covering the chest, waist or abdomen with this little dress. It depends on what you finally want and what you give up when shooting.

For example, when taking a backlight photo, it is decided to have a background, and the person in the foreground may only become a black shadow; If you decide to have a prospect, the background will be bright and all the blue sky and white clouds will be bright.

So make it clear that these three methods used in photometry are only auxiliary references and tools to help you make a choice. There is no metering method to say that the foreground and background of backlit photos can be taken care of by spot metering or area metering.

It's like calculating your age data with a pen, abacus or calculator, and the results are the same.