Why can I adjust the lens height with the big picture chasing the small picture?

mirror

success

be just like

1. Optical center, principal axis, focal point and focal length of lens

Lens is an optical device that controls the light path and imaging through the refraction of light. It can be divided into convex lens and concave lens, as shown in figures 1 1- 13 and11-/4.

(1) optical center: the center of a thin lens, represented by the letter O. Any light passing through the optical center without changing its original propagation direction is called the optical axis of the lens.

(2) main shaft; Both sides of the lens are parts of two spherical surfaces. The optical axis c 1c2 passing through the centers of two spherical surfaces is called the principal axis of the lens. Other optical axes are called secondary optical axes.

(3) Focus: The point where light rays parallel to the main axis converge on the main axis after passing through the convex lens, which is called the focus of the convex lens and is represented by f (Figure 1 1- 13). Light rays parallel to the principal axis will diverge after passing through the concave lens, and these divergent rays will also intersect at a point when extending in the opposite direction, which is called the focus of the concave lens (Figure 65438). Because the focus of concave lens is not the point where light really converges, the focus of concave lens is virtual focus. The convex lens or concave lens has a focal point on both sides, and the two focal points are symmetrical about the optical center.

(4) Focal length: The distance from the focal point of the lens to the optical center is called focal length, which is expressed by F 。

2. The influence of lens on light

From the figures 1 1- 13 and 1 1- 14, it is easy to see that the convex lens converges light and the concave lens diverges. But sometimes it is not easy to see that it is necessary to correctly understand the convergence effect of convex lens and the divergence effect of concave mirror, as shown in figure 165438. Although the original divergent light still diverges after being refracted by the convex lens, the outgoing light deflects relative to the incident light in the principal axis direction (without the convex lens, the outgoing light continues to diverge in the direction of the original incident light), which still reflects the convergence function of the convex lens. Similarly, as shown in figure 1 1- 16, the original converged light is still converged after being refracted by a concave lens. However, compared with the incident light, the outgoing light deviates from the main axis, which reflects the divergence of the concave lens. In figure 1 1- 17 and figure 1 1- 18, parallel light passes through a convex lens and a concave lens respectively.

Therefore, we can judge the properties of the lens according to whether the outgoing light is biased towards the main uranium compared with the incoming light.

3. Lens imaging mapping method

The image of an object consists of images formed by various object points on the object. The drawing method of object point imaging is as follows: draw the symbol, optical center, principal axis and focus of the lens, select a point from the object as the object point (generally the upper or lower end point of the object), take any two of the three special rays emitted by the object point, and the intersection point of the refracted rays (or the intersection point of the reverse extension lines) is the real image (or virtual image) of the point.

(1) The light parallel to the principal axis passes through the focal point after refraction;

(2) The light passing through the focal point is refracted and parallel to the main axis;

(3) After the light passes through the lens, the direction of passing through the optical center remains unchanged.

Note: (1) image point is the intersection of refracted rays from the same object point after passing through the lens, not the intersection of refracted rays from different object points.

(2) When imaging a concave lens, don't misunderstand that "the light passing through the focus is refracted and parallel to the main axis" as shown in figure11,because in this way, the outgoing light is biased to the main axis relative to the incident light, and the concave lens becomes a "convergent lens". The reason for this error is that the meaning of virtual focus of concave lens is not correctly understood.

The position of lens imaging can be calculated by lens imaging formula.

(1) lens imaging formula:

U in the formula is the distance from the object to the optical center, which is called the object distance; υ is the distance from the image to the optical center, called the image distance; F is the focal length of the lens.

(2) Magnification: The ratio of the length of the image to the length of the object is called the magnification of the lens, which is expressed by m, that is

m

& gt

0 means it looks enlarged; m

2f

2f

& gt

υ

& gt

f

shrink

small

u

=

2f

υ

=

2f

Equivalent to the object

f

& lt

u

υ

& gt

2f

let go

big

u

=

f

υ

=

∞

No imaging

f

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u

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f

υ

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On the same side of the object

let go

big

straight

stand

empty

be just like

amplifier

concave lens

anywhere

f

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υ

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shrink

small

f

& lt