Optical knowledge in the human eye

More than 80% of human cognition comes from visual information. If the human body is compared to a precision instrument, there is no doubt that the eye is a precision camera on this instrument. It has perfect "lens" -- eyeball and super intelligent "processor" -- brain.

In simple terms, our eyes can be divided into two parts: the white eye and the black eye, and the black eye can be divided into the pupil and iris. The black dot in the middle of the human eye is the pupil that we say, and the colored thing around the pupil is the iris. The color of the eye that we usually say refers to the color of the iris, such as the brown and black iris that we usually see, and the different shades of blue in Europe and The United States and so on. Iris has obvious personality differences. Iris recognition in modern security system is to extract and identify iris information by combining infrared and night vision imaging. Compared with eye pattern recognition and eye recognition, iris recognition has the highest security level. It is believed that the iris is fixed between 6 and 18 months after birth and cannot be altered by surgery that does not seriously affect vision.

The specific structure of the eyeball is very complex, and its optical imaging process is also very complex. From the perspective of stereo, if the eye is compared to a simple camera, then the pupil is equivalent to the aperture of the lens, controlling the amount of light into the size; The lens acts as a lens through which light enters the back of the eye; The retina acts as the camera's sensor, receiving light signals from the outside world.

In the simple analysis of the eyeball, we can adopt the Galstran simplified eye model, which reduces the eyeball to a single refraction sphere with a radius of curvature of 5.7mm and a refractive index of 1.333. In this model, the focal length of the human eye is about 16mm. The ciliary muscle of the eye can change the shape of the lens to change the focal length. In other words, the human eye is equivalent to a 16mm ultra-wide Angle camera with variable focal length. The pupil of the eye responds to light and shade by adjusting the amount of light entering the eye, which is equivalent to the aperture of the lens. The maximum size of the pupil of the human eye is around 6mm and the minimum size is around 2mm. The aperture value of the human eye can reach 8.3 in strong light and 2.1 in weak light. Because the length of the eye varies with different lighting, the actual aperture can vary.

Only a very small area of the retina of the human eye is used for light sensitive, that is, the macula area, equivalent to the CCD or CMOS camera, regardless of the dynamic range of light and shade, gray or color, the performance of the macula area is absolute dust, the cells in the macula area can feel the difference of light and shade signal ten thousand times as well as thousands of gray level gray signal. Human eyes are 600 times more sensitive in the dark than they are in the daytime, which is still low compared to nocturnal animals such as owls.

Compared to today's hd cameras, such as a camera that takes a selfie with 20 million soft lights on the front, can a human eye camera "illuminate your beauty"? The pixel of the camera we talk about is the sum of the pixels on the whole detector, but what the human eye actually sees clearly in the working state is only a point, and there are 7 to 10 million pixels concentrated in this place alone. Ignoring the storage of information, the pixel of the human eye is about 576 million. Not to mention the human brain, the "central processing unit" of intelligent information processing, analysis, filtering, discrimination, up to the highest level of appreciation.

This article from the Cnomax Vision lens: https://www.industrial-lens.com/Industrial-lens-news.html