I am a beginner in photography, and I use a Canon 500d camera. Who can tell me under what circumstances to take pictures with a camera, such as M files and P files and AV files …

You can use any file under any circumstances.

AV files, the depth of field is decisive.

TV files, decisive action.

P-file means that the camera manufacturer has stored multiple exposure combinations. When taking pictures, the camera will give the most suitable aperture and shutter combination after metering. In P mode, the aperture and shutter are adjustable, but they cannot be adjusted separately, but are combined into one. That is to say, in P mode, if the aperture size is manually adjusted, the shutter speed will change with the aperture size. If you manually adjust the shutter speed, the aperture will also be adjusted with the shutter speed.

Advantages: fast and convenient. Because the camera integrates a variety of exposure combinations, it saves people the time of manual adjustment. If you are not satisfied with the photos, you can manually adjust the exposure combination.

Disadvantages: When shooting, the camera gives what it thinks is the "best" exposure combination, but sometimes this combination can't make an ideal film and can't express the photographer's thoughts. Although the aperture shutter can be adjusted, it cannot be adjusted separately. Only the combination of aperture shutter is adjusted. Some special scenes or films with special effects can't be shot with P file, which is why the camera still has M file.

M file, fully manual, needs the knowledge of photometry, exposure and light ratio as the backing.