Basic Principles of focus (I)

1. Focus)

When parallel light is injected into a convex lens, the ideal lens aggregates all the light to a point, which is called the focus. The focal length is the distance from the focal point to the convex lens optical center.

2. Circle of confusion)

Before and after the focus point, the light from the aggregation to the diffusion, the point of the image from the circle to the point, and then spread to the circle, the front of the focus and the back of the circle, is called the dispersion circle.

If the circle is small enough, it can still be seen as an image. The diameter of the acceptable dispersion circle is called the permissible circle of confusion ).

There is a great relationship between the scenes that people can see with the naked eye and the distance between watching. if the diameter of the circle is smaller than the human's ability to identify, the human eyes will feel clear at that time, this circle is called the allowable dispersion circle.

The depth of field is directly related to the size of the dispersion circle.

3. depth of field)

In imaging, the meridian head is clearly imaged when it is called a plane, and the foreground and background of the focus are also imaged on the focal plane, as long as their imaging dispersion circle diameter is less than or equal to the allowable dispersion circle diameter, we will think it is clear, and this

The range of the clear area is the depth of field.

Depth of field: before and after the subject, the image has a clear range, and the scenes in this range are imaged on the focal plane, all within the limited range of allowable dispersion circle.

1. Short focal length and large depth of field

2. Small Aperture and large depth of field

3. Stay away from focus and have a large depth of field

The above shows that the rear depth of depth> the foreground is deep.

(1) Lens Aperture: the larger the aperture, the smaller the depth of field; the smaller the aperture, the larger the depth of field.

(2) lens focal length: the longer the lens focal length, the smaller the depth of field; the shorter the focal length, the larger the depth of field.

(3) shooting distance: the longer the distance, the larger the depth of field; the closer the distance, the smaller the depth of field.