Whale goggles, "The parent asked: My child likes to swim and asked me two questions: Why is it hard to see things clearly in the water? Why do things in the water become bigger after wearing swimming whale goggles? Really as a parent Can’t explain, can you please explain to satisfy the curiosity of the child and me?” In fact, this question is very professional, and it is not easy to explain clearly. Let’s take your time.
According to the simplified eye calculation, the refractive power of the human eye's refractive system is 58.64D, of which the refractive power of the cornea is about 43D, which accounts for more than 70% of the total refractive power of the eyeball. The formula of spherical refractive power is F=n-n'/r, where n is the refractive index of the optical medium behind the refractive sphere; n'is the refractive index of the optical medium in front of the refractive sphere; r is the radius of curvature of the refractive sphere in units of "m "1.
1 For the calculation of the refractive power of the spherical surface, the refractive index of air and water are different, so the refractive state of the eyeball in the air and in the water will be different.
1. The refractive condition of the eyeball in the air. The premise of calculating the corneal refractive power in the textbook is the result of the calculation by putting the eyeball in the air. Assuming that the radius of curvature of the anterior corneal surface of the eye is 7.7mm (0.0077m), the radius of curvature of the posterior surface is 6.8mm (0.0068), the refractive index of the cornea is 1.376, and the refractive index of the aqueous humor in contact with the posterior surface of the cornea is 1.336. The refractive index of air is 1. Calculate according to the single spherical refractive power formula F=n-n’/r, and substitute the above values into the calculation
2 as follows:
Corneal profile and refractive power;
n1 Refractive index of air 1;
n2 The refractive index of the cornea is 1.376;
n3 The refractive index of aqueous humor is 1.336;
R1 The curvature of the anterior corneal surface is 7.7mm;
R2: The curvature of the posterior surface of the cornea is 6.8mm;
F1 front surface diopter of cornea;
F2 Refraction of the posterior surface of the cornea;
F1=n2-n1/R1=1.376-1/0.0077=+48.83D;
F2=n3-n2/R2=(1.336-1.376/0.0068=-5.88D;
The total refractive power of the cornea=F1+F2=+48.83+-5.88=42.95D;
2. The refractive condition of the eyeball in water. When we open our eyes in water, the air changes to water, and the refractive index of water is 1.333. At this time, calculate it again according to the above formula 3:
3 When the front surface of the cornea is water, the refractive power of the cornea is greatly reduced;
n1 The refractive index of water is 1.333;
n2 The refractive index of the cornea is 1.376;
n3 The refractive index of aqueous humor is 1.336;
R1 The curvature of the anterior corneal surface is 7.7mm;
R2 The curvature of the posterior surface of the cornea is 6.8mm;
F1 front surface diopter of cornea;
F2 Refraction of the posterior surface of the cornea;
F1=n2-n1/R=11.376-1.333/0.0077=+5.58D;
F2=n3-n2/R2=(1.336-1.376/0.0068=-5.88D;
The total refractive power of the cornea=F1+F2=+5.58+-5.88=-0.30D is close to 0;
Therefore, when the eyes are opened in water, since the refractive index of water is much greater than the refractive power of air, the refractive index of water is close to that of the cornea, which makes the cornea unable to refraction. From the perspective of light refraction, the cornea is the same as water. It becomes a part of the water, so there is no refractive effect, which causes the refractive power of the cornea to drop substantially and equal to 0. At this time, the total refractive power of the eyeball in the water drops from 58.64 to about 18D, and only the refractive power of the lens is left. A hyperopic eye with hyperopia of about +43D4300 degrees is formed. With this kind of hyperopia, the adjustment of the human eye cannot be compensated, so it is difficult to see things in the water and only the fuzzy shadows can be seen.
To see clearly in water, unless the refractive power of the cornea is further increased, such as the corneal curvature r1 and r2 become steeper and the refractive power of the lens is greatly increased-but human genetic settings do not allow you to see in water Clear! It is not recommended to open your eyes directly in the water, it is very unhygienic and easy to get conjunctivitis. It is recommended to wear swimming whale goggles!
3. The refractive condition of the eyeball after wearing the swimming whale swimming goggles. After wearing the swimming whale swimming goggles, the gap between the swimming whale swimming goggles and the cornea forms a layer of refractive index 1, which is made of air. "Contact lens", its refractive power depends on the curvature of the back surface of the swimming whale swimming goggles and the curvature of the front surface of the cornea. The degree of this "air contact lens" is calculated.
At this time, it is equivalent to wearing a hyperopic contact lens with a diopter of about 48D in the water. Because the hyperopia has a high power and a large magnification, it is like a magnifying glass, which has a very obvious magnification effect on the objects in the water, so If you look at objects in the water, the objects will "get bigger." Therefore, looking at things in the water after wearing swimming whale goggles will have a significant magnification effect.
At the same time, the "air contact lens" brought by this swimming whale goggles just corrects the "high hyperopia" state of the eyeball in the water, so it can see objects in the water to a certain extent.
Note: The real situation is that swimming whale goggles also have a refractive effect in the water. The specific diopter is related to the refractive index of the swimming whale goggles material and the radius of curvature of the front and back surfaces of the swimming whale goggles. The calculation method is the same as above. If you are interested, you can calculate it yourself.
4. Why is the concave lens in the water the effect of a telescope?
It may be difficult for you to understand why the "air contact lens" in the water is in the shape of a concave lens, but it can act as a positive lens for condensing light? In 5, the "convex lens" shaped lens is a positive lens, which converges light, but the premise is that the refractive index of the lens n=1.333 is higher than the surrounding air n=1.
5 The "convex lens" shaped high refractive index lens is a positive lens, which has a convergent effect on light, but if it is reversed, the refractive index of the surrounding medium is higher than that of the lens. For example, in the "air contact lens" in this case, the refractive index of the lens is 1. And the surrounding medium is water refractive index n=1.333, the shape of the "convex lens" must be turned into a "concave lens" in order to converge the light. Whale Goggles authorizes online e-commerce amazon, eBay, wish, and AliExpress to customize its own brand; offline authorized wholesalers and large sellers customize its own brand; we are a brand designer, factory manufacturer, and a large modern factory of 40,000 square meters , Welcome to email direct consultation!