A lens is a transmissive optical tool that employs refraction to focus or disperse light beams. Simple lenses are made of a single transparent piece, while compound lenses are made of multiple simple lenses aligned along a single axis.
There are three basic types of optical lenses: spherical, aspherical, and cylindrical. Each of the three categories has distinctive qualities that make it appropriate for various use cases.
Definition of Aspherical Lens and Spherical Lens
1. Spherical lens: Spherical lenses, commonly known as singlets, are optical lenses with a spherical surface and a constant radius of curvature throughout the entire lens. Depending on the lens design, they are built so that the light entering them either diverges or converges.
The negative focal length of concave spherical lenses causes incident light to diverge (creating a virtual image). While the virtual images created are greatly magnified, the real ones created are sharply focused.
2. Aspheric lens: Any lens with surfaces that are not sphere-related is referred to as an asphere. However, in this context, the term "asphere" refers particularly to the subset of lenses that are rotationally symmetric optics with radial variations in the radius of curvature. Aspheric lenses enhance image quality while requiring fewer optical components.
In recent years, the incorporation of aspheric lenses over spherical lenses in optical designs has become more popular. A single aspheric element can replace two or three spherical elements in a design while maintaining or even improving the imaging system's performance.
According to the BIS Research analysis, the global high precision asphere market was valued at $2,400.0 million in 2021 and is expected to reach $5,214.0 million by 2031, growing at a CAGR of 8.1% between 2022 and 2031.
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Most aspherical lenses are used in manufacturing optical instruments, vehicles, telescopes, and binoculars. They also aid in achieving improved focus, a broader focal length range, and fewer aberrations due to diffractive factors.
Various end users, such as automotive and optical industries, are moving away from the conventional usage of spherical lenses to aspherical lenses, which increases the accuracy and usefulness of a product.
What are the benefits of an aspheric lens over a spherical lens?
Major advantages of the aspheric lens are as follows:
• It offers decreased quantity of lenses in a design
• It enables easier assembly of the lens
• It significantly cuts down on stray light falling on the lens
• It discards spherical aberration (a departure from the normal path of light rays), which is the general flaw of a spherical lens. The amount of spherical aberration correction provided by a single aspheric lens is equivalent to that provided by two or more spherical lenses.
• It boosts the system's efficiency and resolution.
Moreover, aspheric lenses are particularly effective in reducing distortion, astigmatism, and other off-axis/field-dependent aberrations in addition to spherical aberrations. This allows for converting complex ten-element designs into very straightforward four or five-element designs.
Types of Aspheric Lenses
There are two different types of aspheric lenses, each with a distinct advantage. For instance, plastic aspheric lenses are perfect for prototype or low volume requirements due to their short lead times, minimal special tooling, and setup.
While precision glass molded aspheric lenses, also known as glass aspherical lenses, are ideal for volume production requirements due to the rapid production of many lenses and low tooling upkeep costs.
The following article goes into further depth about the two primary aspherical lens types:
1. Glass aspherical lens: To create glass aspheric lenses, the glass material is heated at a high temperature, where it is converted to plastic and then molded using an aspheric mold.
Glass aspherical lenses are more versatile than other aspherical lenses because they come in a wider range of refractive indices. These lenses have better casing capabilities due to their ability to modify their edges to create friction, which results in a superior metal-glass casing.
A glass aspheric lens differs from a regular spherical lens because it can rectify spherical aberration.
These aspheric lenses are frequently used for observatories, research facilities, and high-end optical equipment applications. Additionally, these lenses are also used in the optical wearables business to create items such as eyeglasses.
2. Plastic aspherical lens: Compared to glass aspherical lenses, plastic aspherical lenses have a smaller market share. Plastic aspheric lenses are reasonably inexpensive because they are mass-produced, can be easily molded, and are easier to coat.
With additional features such as ultraviolet (UV) resistance and scratch resistance to the raw materials of the plastic aspherical lenses, these lenses are more durable and have a longer lifespan.
Since plastic lenses are lightweight and can be combined with mounting components to form a single element, they are advantageous. The plastic aspherical lens has a narrower range of refractive index and can only pass wavelengths between 400 and 700 nanometers without affecting the image's focus.
These lenses are utilized in a variety of end-use products, including cars, binoculars, laptops, and cell phones. Plastic aspheric lenses must be properly treated to make an operational aspheric lens because they are not thermally stable and pressure-resistant like glass.
Plastic aspheres can also be produced using various techniques, including plastic injection molding, compression molding, diamond turning, and others. Molten plastic is injected into an aspheric mold during the process of plastic injection molding.
Conclusion
As discussed, the capacity of aspheric lenses to correct spherical aberration, an optical phenomenon that causes incident light rays to focus on various spots while producing an image, is perhaps the most noteworthy advantage.
Due to this advantage, the global high precision asphere market has undergone a profound transformation. Additionally, the changing demands of the end-user industry have revolutionized the industry.
In the future, the growth in the global high precision asphere market is expected to be driven by the deployment of high precision asphere in mobile phones and automobiles.
