The most direct diagram:
1. Diffusion circle
Before and after the focal point , the light begins to gather and diffuse, and the image of the point becomes blurred, forming an enlarged circle, which is called the circle of diffusion .
In reality, viewing and shooting images are observed in a certain way (such as projection, magnification into photos, etc.), and the image perceived by the naked eye has a great relationship with the magnification, projection distance and viewing distance. If the diameter of the circle of confusion is smaller than the discrimination ability of the human eye, the blur produced by the actual image within a certain range cannot be recognized. This unrecognizable circle of confusion is called the allowable circle of confusion.
2. Depth of field
There is an allowable circle of confusion before and after the focal point, and the distance between these two circles of confusion is called the depth of focus , which corresponds to the area in which the image still has a clear range before and after the subject (focus point), which is the depth of field.
The depth of field changes with the focal length of the lens, the aperture value, and the shooting distance. For a fixed focal length and shooting distance, the smaller the aperture (the larger the aperture value), that is, the smaller the diameter of the lens, the larger the depth of field , regardless of the amount of light passing through the lens.
3. Aperture
Also known as "relative aperture," a camera's lens uses a multi-blade assembly to control the amount of light entering the lens, called the aperture.
reference
1. The magic paradise of light and shadow -- interesting lens
The relationship between SLR aperture, focal length and depth of field- Know about