What is the focal length of the lens for human eyes?

People's front and back focal lengths are different, with the front focal length f = 17. 1mm and the back focal length f' = 22.8 mm.

It is difficult to calculate the eye accurately, because the eye is a complex optical system with multiple refractive surfaces, and the refractive indices between them are different. The actual calculation is often simplified and approximated, and several optical models of eyes can be obtained, among which a. Gullstrand simplified eye is a common optical model of eyes.

The simplified eye regards the eye as a single spherical refractive system, as shown in Figure 4- 16. It is considered that the eye is composed of only one medium, with a refractive index of 1.33 and a radius of curvature of 5.7 mm. The front focal length f = 17. 1mm and the back focal length f' = 22.

The unequal focal length of the eye is caused by the unequal refractive index of the object side and the image side of the eye.

Extended data:

The standard lens gives people a vivid visual effect picture, so it is often used in actual shooting. On the other hand, because the picture effect of the standard lens is very similar to the visual effect of the human eye, the picture effect taken with the standard lens is very ordinary, and even can be said to be "plain".

It is difficult to get the dramatic effect of the rendered picture like a wide-angle lens or a telephoto lens. So it is not easy to take vivid photos with standard lenses. Even experienced photographers think it is not easy to use standard lenses well.

However, the visual effect of the standard lens has a natural sense of closeness. When shooting with the standard lens, the distance from the subject is moderate, so it is widely used in ordinary landscapes, ordinary portraits, snapshots and other photography occasions, and it is also the most common commemorative photo.

More is shooting with a standard lens. In addition, what photographers often overlook is that the standard lens is also a lens with good imaging quality, which is very effective for showing the details of the subject.

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