Introduction camera

Generally speaking, the working principle of a camera is to use the optical imaging principle to image an object on a photosensitive material through a photographic lens. The following will briefly introduce the principle of photographic optical imaging: human understanding of the nature of light, the propagation of light and the principle of lens imaging.

Human understanding of the nature of light has gone through a long and tortuous process. In the whole18th century, the particle flow theory of light is still dominant in optics. It is generally believed that light is composed of tiny particles, which are emitted from point light sources and radiate in all directions in a straight line. /kloc-At the beginning of the 9th century, the works of Yang and Fresnel gradually developed into today's wave optical system. Now, the understanding of the essence of light is that light, like the real thing, is a kind of substance, which has both the properties of wave and particle (quantum), but as a whole, it is neither wave nor particle, nor a mixture of the two.

In essence, light is no different from ordinary radio waves. Like electromagnetic waves, light is a shear wave, that is, the vibration direction of the wave is perpendicular to the propagation direction. Luminous body is the emission source of electromagnetic wave, and the electromagnetic wave emitted by luminous body propagates to the surrounding space, similar to the wave generated by water wave fluctuation. The distance between two points with maximum or minimum intensity is called wavelength, which is denoted by λ. The time required to propagate a wavelength is called a period, which is represented by t, and the period is the time required for a particle to complete a vibration. The number of vibrations in 1 sec is called frequency, which is expressed by nu. The distance that vibration travels through 1s is called velocity, which is represented by "v". There are the following relationships among wavelength, frequency, period and speed:

v=λ/T，ν= 1/T，v=λν

It can be seen that the wavelength of light is inversely proportional to the frequency. In fact, light waves only account for a small part of the entire electromagnetic wave band. The electromagnetic wave with the wavelength of 400 ~ 700 nm can be felt by human eyes, which is called visible light. Beyond this range, the human eye will not feel it. Different wavelengths of visible light produce different color sensations in our eyes. According to the wavelength from long to short, the color of light is red, orange, yellow, green, cyan, blue and purple. The propagation speed of electromagnetic waves with different wavelengths in vacuum is exactly the same, and the value is c = 300000 km/s.

Here are some basic laws of geometric optics-the law of light propagation:

(1) The law of linear propagation of light in a uniform medium, that is, light travels along a straight line, that is, light is a straight line in a uniform medium. The phenomenon of linear propagation of light can be seen anytime and anywhere in daily life, such as objects turning into shadows after being irradiated by light, pinhole imaging and so on. The linear propagation of light leads to the concept of light.

(2) The Law of Independent Propagation of Light The propagation of light is independent. When different rays pass through a certain point in the medium from different directions, they do not affect each other. When two rays converge at a certain point in space, its function is simply superposition. This characteristic of light makes the light from all points of the object enter the camera lens without affecting each other, forming an image on the imaging plane.

(3) Law of Reflection of Light When light propagates to the interface of two different media, it will change the propagation direction and reflect the light. The law of light reflection points out: ① The normal lines of incident light, reflected light and the projection points of light on the interface are in the same plane, and the incident light and reflected light are located on both sides of the normal line respectively.

② The shooting angle and reflection angle are equal. The angle between the incident light and the normal n is recorded as the incident angle, which is expressed by I; The angle between the reflected light and the normal n is recorded as the reflection angle, which is expressed by α. Then i=α. The reflection of light is also reversible. If light is incident on the interface against the original reflected light, it will be reflected against the original incident light. According to different interfaces, reflection can be divided into directional reflection and diffuse reflection. Light is incident on a bright plane mirror from one direction, all incident points fall on the same plane, and all reflections are in the same direction, which is called directional reflection. When light is projected from one direction onto a rough surface (such as ground glass surface), because the rough surface can be regarded as composed of many facets with different angles, the light is reflected from different directions, which is called diffuse reflection. However, it should be noted that in the diffuse reflection phenomenon, every ray still follows the reflection law.

The reflection of light plays a very important role in photography. For example, people themselves do not emit light, but when light shines on people from all angles, it can be reflected from all angles. We often use reflected light to take pictures, which is to follow the reflection law of light.