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Aspheric lens for goggles
explained in detail

As someone who uses eyeglasses, you may have come across terms like aspheric positive or aspheric negative lens. Although the terms may be intimidating at first, fear not as we explain what they mean in detail. This makes it easy for you to understand the science behind your eyeglasses. We also incorporated the same concept in developing the Optic Kit for your corrective goggles. You will also learn that the aspheric lens has superior properties as compared to spherical lens. Therefore keep that at the back of your mind next time you want to use the aspheric lens for corrective goggles, aka Optic Kit. In addition we break down why some lens powers are assigned a positive value (aspheric positive) and some a negative value (aspheric negative).

Difference between aspheric lens and spherical lens

Difference between
aspheric lens and spherical lens

Spherical lens

Spherical lens with such properties is called a spherical lens because its curvature follows a perfect spherical figure

Think of a perfect sphere and as you know every point on its surface is exactly the same distance from the centre. If you make a vertical section of the sphere at any point you are left with a flat cut surface on one side. The other curved surface still represents the whole perfect sphere and can be extrapolated to reproduce the original perfect shape. A lens with such properties is called a spherical lens because its curvature follows a perfect spherical figure.

Aspherical lens

Aspherical lens is exactly the opposite because its curvature doesn’t follow a perfect sphere hence the term aspherical

On the other hand an aspherical lens is exactly the opposite because its curvature doesn’t follow a perfect sphere hence the term aspherical. The points on the surface of the curve don’t have a common centre. It may seem paradoxical but in optics this aspheric lens is the best choice for your prescription goggles, available as Optic Kit. You will learn shortly why aspherical lenses are superior. The technology was first rolled out in applications like making movie cameras around 1956 following the ability to reproduce a crystal clear image. We use the same type of lens in Optic Kit as a stick-on aspheric lens for corrective goggles.

Why is the aspheric lens superior ?

Refraction

Before you learn about the benefits of the aspheric lens you should be aware of an important property of light which is refraction. Refraction is when light is bent as it passes through a medium. As light rays pass through a lens, they traverse from air then through the lens (usually made of glass or plastic) then exit into another medium. This may be air again or the tissues of the eye. Due to different densities of these media, light rays are bent or refracted.

Focal point

Focal point, due to the curvature of the lens, whether it’s spherical or aspherical

Due to the curvature of the lens, whether it’s spherical or aspherical, light rays from an object are refracted as they pass through the lens. In ideal settings, these light rays tend to find a common point called a focal point where they cross. The lens can be a converging lens (convex lens), which brings the light a focal point after the exiting the lens as shown below. It can also be a diverging lens (concave lens), which scatters light rays away from a focal point.

Problem with a spherical lens – optical aberration

A lens has an outer surface, or the ingress surface where light rays first hit the lens and the egress surface where they exit the lens. The light rays are refracted as they cross these surfaces (see above for clarification). However, as you know it’s difficult to get a perfect system in science, scientists discovered something interesting. In a perfect spherical lens the degree of refraction of light rays does not create a perfect focal point as you move away from the centre of the lens. This is due to a phenomenon called optical aberration and unfortunately it’s created that way.

The solution – aspheric lens

In an ideal lens all the lines of light entering a lens should be refracted at angles that create a perfect focal point. Unfortunately this is not the case with a spherical lens and solution is to use an aspheric lens. This is designed in such a way which corrects the discrepancies created by the ingress and egress surfaces, hence producing a perfect single focal point. However, a perfect curvature is sacrificed in the process due to the aspherical property.

Benefits of using an aspheric lens

You now know how an aspheric lens is perfect when you want to produce a perfect focal point. Let’s look at the benefits in real applications like aspheric lens for corrective goggles. If you enjoy performing outdoor activities that require eye protection or you want carry out a project in a workshop we recommend Optic Kit. It uses an aspheric lens for corrective goggles similar to what is used in sunglasses and the benefits are described below.

  • As more optic power is needed, a spherical lens becomes thicker than an aspheric lens which means more weight. Aspheric lenses are about 11% thinner for the same optic power.
  • Spherical lenses also become more curved which may not be cosmetically appealing if you are given eyeglasses with such lenses. On the contrary, aspheric lenses are flatter.
  • Have you ever seen someone whose eyes get magnified when wearing eyeglasses? Yes, those have spherical lenses and that’s one reason why people opt for aspheric lenses, which don’t give that effect. Fortunately, we made sure Optic Kit uses the aspheric technology to avoid such bug eyes, making eyes look natural and proportionate.
  • The edges of aspheric lenses are thinner and look nicer as compared to spherical lenses which become thicker as more optic power is required.
  • Aspheric lenses eliminate optical aberration hence there is no distortion of an image as what would happen with spherical lenses. In the end there is better image quality and better peripheral vision.
  • You get more options for selecting a frame for your eyeglasses when using aspheric lenses.

Measure of optic power – the diopter

Another term you need to learn about is the Dioptre, which is a unit of optic or lens power. By definition a Dioptre is the measurement of the lens’s ability to bend or refract light that passes through its surfaces. The more the light is bent, the smaller the focal length (in meters) and the greater the Dioptres. There is a baseline 1 Dioptre lens which has an optic power which creates a focal point 1 meter from the centre of the lens. Any unit increase represents a 25% increase in optic power. To get the picture look at the formula of calculating Dioptres:

Formula

Dioptre = Inverse of the focal length in meters

Therefore in other words:

3 Dioptres = 75% increase in power (1.75 times) of a 1 Dioptre lens = focal length a third of 1 meter

5 Dioptres = 125% increase in power (2.25 times) of a 1 Dioptre lens = focal length a fifth of 1 meter

The aspheric lens for corrective goggles which we market as Optic Kit has a specific optic power so you easily choose the strength you need.

Positive diopter and negative diopter

It’s not enough to assign a magnitude to a lens without indicating the behavior of the light as it passes through it. As you learnt in the first section, a lens can either be converging or diverging. These two properties are represented by a sign, either positive (+) or negative (-). A converging lens, which is convex, is used to manage short-sightedness and the power of the lens has a negative sign. On the other hand, a diverging lens which is concave has a negative sign, and is used to manage long-sightedness.

This means if you see a lens which is aspheric +3 Dioptres,
remember that:

1
It’s a converging lens
2
The focal length is a third of 1 meter or 1.75x more powerful than a +1 Dioptre lens
3
It is an aspheric lens

On the contrary, if you see a lens aspheric -5 Dioptres,
this means:

1
It’s a diverging lens
2
The focal length is a fifth of a meter or 1.75x more powerful than a -1 Dioptre lens
3
It is an aspheric lens

The optic Kit

As you have already learnt at the beginning, the Optic Kit is a perfect aspheric lens for corrective goggles as it uses the corresponding optic power of your eyeglasses. This means if you are either short-sighted or longsighted, we have the perfect Optic Kit for you. The other good news is that it is safe with details on how to use it outlined in this article. I’m sure now you can confidently decode the terminology that is used for your eyeglasses which makes it easy to use or product tailor-made for you.

Conclusion

Our thrust is to deliver to you a perfect aspheric lens for corrective goggles and Optic Kit is the answer. With this stick on accessory you can explore the world, be it cycling, swimming or any application where you need protection from the elements. Our laboratory experts machined the Optic Kit to conform to the specifications prescribed to you by your doctor. Therefore you shouldn’t expect any adverse reactions and customers have provided positive feedback. Be liberated and experience a new level of technology by ordering your Optic Kit now. It will quickly be a must-have for any sports enthusiast or DIY individual.