How far can the human eye see ?
How far can the human eye see ?
The human eye is actually a “super camera” with up to 576 million pixels. The human eye can distinguish 10 million colors.
In general, visual acuity is the ability of the eye to distinguish the shape and existence of an object. There are four types of eyesight:
- Minimum visibility threshold: how small you can see
- Minimum separation threshold: How narrowly the intervals can be viewed separately
- Minimum readable threshold: how small letters and figures can be discriminated
- Vernier visual acuity: How fine straight lines and contour deviations can be detected
A normal visual acuity test measures the minimum separation threshold, and a Randold ring is used to see if the break is visible.(how far can the human eye see) The visual acuity of a person who can distinguish a Randolt ring with a diameter of 7.5 mm and a gap of 1.5 mm from a distance of 5 m is 1.0. The distance between the cuts of the Randolt ring optotype with a visual acuity of 2.0 is 0.75 mm, so it is surprising to see a cut of less than 1 mm from a distance of 5 m.
The Randold ring is a target defined by the 1909 International Ophthalmology Society, and is shaped like the letter C. The size of the Randold ring, which shows a visual acuity of 1.0, is 7.5 mm in diameter, 1.5 mm in thickness, and 1.5 mm in width of the cut. Looking at this from a distance of 5m, the viewing angle is 1′(1/60 degrees).
Histologically, the photoreceptor cells of the retina that sense light include pyramidal cells and rod cells. The pyramidal cells work when bright and are said to have about 5 million cells on the retina.
Mainly color vision and figure shape identification (≒ visual acuity). On the other hand, rod cells work when it is dark, and it is said that there are about 100 million rod cells on the retina, which mainly distinguish between light and dark and sense movement.
Visual acuity depends on pyramidal cells, and it is said that the diameter of the pyramidal cells in the fovea centralis of the retina is about 2 μm and the visual angle is about 30 seconds.
Since a visual acuity of 1.0 is equivalent to one minute when converted to a visual angle, it is about two pyramidal cells that recognize the break in the Randold ring with a visual acuity of 1.0. In other words, at the cellular level of the retina, it seems that the visual acuity of about 2.0, which is equivalent to the size of one pyramidal cell, is the limit.(how far can the human eye see)
However, in reality there are people with better eyesight.
About 10 years ago, there was a TV program of the Japanese TV series called “World ☆ Records“, in which a 26-year-old man from the Kenya Masai tribe set a record of 6.0 eyesight. 6.0 means that you can read the target of 0.6 on the normal 5m visual acuity chart from a distance of 50m.
How far can the human eye see if someone has a very good eye?
It is indispensable to see things in life, but at that time, eyesight is a concern .
By taking a visual acuity test, you can objectively obtain information about “how many eyesight“. If you have poor eyesight, adjust your glasses and contact lenses based on your eyesight.
Many visual acuity charts used for testing have an upper limit of 2.0, but what is the actual upper limit of human vision?
Visual acuity = ability to distinguish between two points
2.Visual acuity numbers
Generally speaking, “visual acuity” is the ability of the eye to distinguish between two points that are separated from each other .
The distance at which the eyes can be distinguished is expressed by the angle at which the two points are reflected in the eye, and this angle is called the visual angle . The unit is minutes (1 / 60th of a degree).
Visual acuity numbers
And the visual acuity is expressed by the reciprocal (= 1 ÷ minimum visual angle) of the shortest recognizable distance (minimum visual angle) . For example, if the minimum viewing angle is 1 minute, 1 ÷ 1 gives a visual acuity of 1.0, and if the minimum viewing angle is 2 minutes, 1 ÷ 2 gives a visual acuity of 0.5.
A distance of 1.5 mm when viewed from 5 m ahead corresponds to a viewing angle of about 1 minute, and if two points closer than this cannot be distinguished, the minimum viewing angle is 1 minute, that is, the visual acuity is 1.0.
In the Randold ring (a shape like C) used in normal visual acuity tests, the cut in the ring is an index of the minimum visual angle, and if it can be correctly identified up to the direction of the 1.5 mm cut, the visual acuity is 1.0, and if it is twice as large, the visual acuity. It will be 0.5, and so on.
Cone cells control vision
The visual information that enters the eye is inside the eyeball.retinaIt is transmitted to the brain from that part.
The photoreceptor cells (cells that convert light into electrical signals) in the retina control vision and color vision.ConeSensing cells and light and darkRodThere are two types of cells .
And the pyramidal cells are in the middle of the retinaFoveaBecause there are many in this part, the eyesight is highest when looking at the center of the visual field.
Distinguish between two points = Information enters into distant pyramidal cells
By the way, in order to identify that two points are separated, two non-adjacent pyramidal cells must react . This is because when two adjacent pyramidal cells react at the same time, the brain recognizes that part as a single point.
Therefore, the distance between two non-adjacent pyramidal cells (the angle formed by ) determines the minimum visual angle of the eye and determines visual acuity.
The more pyramidal cells are gathered, the shorter the distance between the pyramidal cells. The total number of pyramidal cells in the retina is about 6 million, but most of them are gathered near the fovea centralis and their diameter is reduced to increase the density.
The diameter of the pyramidal cells in the most dense part is 1.0 to 1.5 μm, and when this value is converted to the minimum viewing angle, it is 0.2 to 0.3 minutes, and the visual acuity is about 3.3 to 5.0 .
The limit of actual eyesight
In reality, it is difficult to accurately estimate the upper limit of vision due to various factors other than the distance of pyramidal cells.
For example, when the brightness of what you are looking at changes, so does your eyesight.
In addition, the light that enters the eye passes through the crystalline lens (the part corresponding to the lens of the camera) and forms an image on the retina, but if the thickness of this crystalline lens is not appropriate, it will not be in focus and the eyesight will deteriorate. (The abnormalities caused by this are myopia and hyperopia ).
By the way, there is a theory that the high visual acuity of the Maasai people in Africa is more related to the environmental factor that the ability to adjust focus is trained by looking at animals in the distance than the genetic factor. For those who want to push the limits of human vision, it may be a good idea to start by training your eyes.
How far can people see? (How far can the human eye see)
First, it depends on how big the thing you are looking at is. The second depends on how high you stand.
On a pure, clear, moonless night, human eyes can see a little candlelight 27 kilometers away;
The farthest celestial body seen in human history so far is GRB 080319B. The celestial body had a gamma-ray burst on March 19, 2008. It was 7.5 billion light-years away from the Earth and its apparent magnitude reached 5.8; in other words, The naked eye saw the light emitted 7.5 billion years ago.
(Jasper Park in the Canadian Rockies is the world’s second largest dark night starry sky reserve. Every autumn is Jasper’s “Star Moon“, one of the most perfect stargazing spots.)
(All the stars that humans can see with the naked eye are in the small yellow circle. Pay attention to the stars that can emit light. On a clear, clear and moonless night, the average half of the sky that can be observed by the naked eye is about 3000 stars. There are about 6000 stars in the celestial sphere that can be seen by the naked eye.)
(The Milky Way over the Chilean Atacama Desert; the world’s dry pole Atacama Desert is also one of the four major stargazing attractions.)
How small can the human eye see clearly?
The theoretical resolution of the human eye is 18-20 arc seconds, and the minimum length that the human eye can distinguish is about 0.1 mm. Ordinary optical microscopes can distinguish up to 1 micron, and the most advanced electron microscopes can distinguish up to about 1 nano-meter.
1 millimeter (mm) = 1000 microns (um); 1 millimeter (mm) = 1000000 nano-meters (nm)
But human beings are by far the only intelligent life in the universe. The greatness of human beings is to invent and explore the unknown with the help of tools.
Mankind invented astronomical telescopes to explore the stars, and mankind invented high-power microscopes to observe the microscopic world.
Below is a group of photos taken by scientists using high-performance microscopes to zoom in on tomatoes, dust, butterflies, and bees.
(The tomato magnified thousands of times seems to have entered a whimsical world).
(After magnified thousands of times, the butterfly’s eyes look like monsters from another world.)
(After magnified thousands of times, the bee feels inexplicable chill and fear.)
(Dust in the house under a high-power microscope.)
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