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How many mm lens is equivalent to the human eye?

The existing answers are not very comprehensive, because human vision itself is a complex system, and there are individual differences between people, and when we discuss vision, we will make different definitions due to different purposes , so it is difficult for us to give an accurate conclusion about how many mm lens is equivalent to the human eye. Here I discuss this issue on several levels.

First of all, from a physiological perspective, the human eye is a lens of about 17mm. This is the conclusion in “Human Physiology” published by Oxford University Press. This conclusion is calculated based on the measured diopter of the human eye. For details, see the original Chapter Eight:

Alternatively, refer to the American Academy of OphthalmologyOptical Properties of the EyeOne sentence.

If you look directly at the anatomical size of the human eye, the front focal length of the human eye is about 17.2mm, and the back focal length is about 22.9mm

But this is obviously not enough to answer the question of the title. When we discuss how many mm lens is equivalent to the human eye, we often discuss the equivalent focal length under the 135 system. First of all, if we simply and crudely calculate according to the length of the diagonal, the retina occupies about 72-75% of the eyeball with a diameter of 22-24mm, and the straightened angle of view is about 120-130 degrees, which is roughly equivalent to 11 A lens around -12mm.

Of course, this does not need to be checked and everyone intuitively knows that it is wrong. In fact, the vision of the human eye is not an ideal circle, but rather an irregular shape due to the occlusion of the eyeball movement limit and the eyebrows, cheeks, and nose. The picture below is also from “Human Physiology”. You can see how non-standard the shape of a standard human eye field of view actually is.

Of course, the above picture only considers the situation of the right eye. If we add the left eye, the result is as follows:

In other words, the viewing angle of the human eyes in the horizontal direction is about 180-220 degrees, and the viewing angle in the vertical direction is about 120-140 degrees. By the way, the 16:9 screen ratio of the 135 system or the movie is determined based on this.

In addition, you can also experience this picture through a small experiment. Put your hands on both sides of your ears, palms forward, and then slowly spread your arms horizontally. If our field of vision is exactly 180 degrees, then the palms are now behind the eyes, theoretically we should not be able to see. But you will find that with the arms open, you will be aware of the palms in your peripheral vision. When you can see the palms in your peripheral vision, slowly raise your hands up, and you will find that you can’t see your palms anymore, because our upper vision is narrower. When you move your hands down, you will find it easier to see your palms because our lower vision is wider.

Speaking of which, is it even more chaotic? And it is getting farther and farther away from the so-called standard lens focal length of 50mm. This is because we have missed an important problem. The photoreceptor cells in the eyes are not evenly distributed, but the farther away from the center, the sparser they become.

The blue line in the picture above represents the cones that are more sensitive to color, and the red line represents the rods that have almost no color vision and are only sensitive to light. It can be seen that it drops sharply after exceeding the 40-degree field of view.

When we combine the above knowledge points together, we have the visual range area as shown below.

It looks like this from above

These two images are from Wikipedia’s Peripheral Vision entry:


Generally speaking, we regard the near peripheral vision, that is, the content within the range of 60 degrees as the normal visual field of human beings. From this range, we enter the visual area where our eyes can be seen together and have a sense of space; the range of about 40 degrees As the attention field of human beings, this is a part of the area with the highest density of visual cells; the range of about 25 degrees is the focus field of view, where we can perceive the color and light and shade changes of the picture at the same time. These three gears correspond to the field of view of 35mm lens, 50mm lens and 85mm lens under 135 system respectively.

Finally, as a colorist, our industry is actually mainly concerned with the two field of view ranges of 2 degrees and 10 degrees. If the shape is only densest in the center of the visual field, then we should only examine this part of the color, so a model of a 2-degree observer is obtained. But more than 30 years later, everyone discovered that human beings’ perception of color will change when the field of view is wider, especially the perception of blue and green will be biased, so there is another 10-degree observer.

Also, the subject mentioned “the object seen by both eyes is the same size when it is adjusted to 70mm”. This is not because of the focal length of the lens, but is affected by the magnification of the viewfinder. About this There is almost a good popular science article, so I won’t repeat it:

Playing with Xiaopang: Light science: chatting about the design of the camera viewfinder

Source: Zhihu www.zhihu.com

Author: Huang Yikai

[Zhihu Daily]The choice of tens of millions of users, to be a big cow to share new things in the circle of friends.
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Further reading:
What is the human eyeball compared to the lens in the SLR?

Is there a difference between a long shot and a single shot?

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