Senior two physics thesis (800 words)

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.