How to use the automatic exposure lock of Canon camera?

Recently, in photography class, Teacher Xie was teaching "Photometric Mode". Canon's friends often discuss with me such issues as how to focus on metering, how to use exposure lock under what circumstances and so on. In order to solve these problems, combined with the knowledge learned in class, I did several experiments at home, took hundreds of photos, and analyzed and compared the EXIF of each photo. I got some perceptual knowledge, and on this basis, I got the following views. I hope that bloggers will criticize and correct the inaccuracies: First, I found that when I half pressed the shutter button, the focusing and metering were completed synchronously, and the focusing was locked. If I don't need to compose music again, I don't need it. When the composition is re-composed, its "focus" remains unchanged with the movement of the lens, but the original photometric results are cancelled and need to be re-measured. Secondly, when the brightness contrast of the scene is very large, in order to shoot a clear subject, it is necessary to measure the subject and use the exposure lock. P 1 The cover of the black book (hereinafter referred to as H) is measured by fixed-point focusing, and the shutter speed of 1/20s is obtained by exposure locking. H's details are very good. P2 is the same as P 1. Spot-metering the cover of the white paper (hereinafter referred to as B), and obtaining the shutter speed of 1/320s by using the exposure lock. B's details are very good. Because the position of the metering point on the book cover is slightly different, the shutter speed will also change slightly. P3 measures light at H point, and obtains the shutter speed of 1/250s without exposure locking. P4 measure B, and get the shutter speed of 1/250s without exposure locking. It may be a coincidence why P3 and P4 have the same photometric values. P3 is the bright part of H and P4 is the dark part of B, so their brightness in the measuring aperture must be the same. Thirdly, the metering result of spot metering is also related to the selection of focusing area. The P5-P8 photos are all in regional focus, and the metering mode is also spot metering. P5 Measure the light of H, and use the exposure lock to get the shutter speed of 1/20s. Same as P 1. P6 Measure B in the field, and use exposure locking to obtain the shutter speed of1125s. It is different from P2 because their photometric points are different. P7 measures light at H point without exposure lock, and the shutter speed is1160s.

P8 measure B, shutter speed1125s without exposure locking. Four, when using evaluation metering, there is no need to use the exposure lock button. Under the setting of evaluating metering, when the shutter button is half pressed, focusing and metering are locked at the same time. This metering mode brings great convenience to shooting. P9 fixed-point focusing, evaluating photometry H, and using exposure lock, the shutter speed of 1/40s is obtained. P 10 fixed-point focusing, H evaluation and photometry, without using the exposure lock, the shutter speed is the same as using the exposure lock 1/40s.

P 1 1 19 autofocus, evaluation B, shutter speed of1125 s obtained by using exposure lock P 12 19 autofocus, evaluation B, obtained without using exposure lock/. 5. When using evaluation metering, the metering point coincides with the "focus" in the picture. Because the focus point is usually on the object surface closest to the camera, you can often get a clear picture. When this foreground is not the subject you want to shoot, you should change the area focus mode or change the metering mode. 6. After pressing the "exposure lock" button, although the button is released, it is still effective for a short time. When shooting other scenes again, wait a few seconds to make the exposure lock invalid (* logo disappears).