#optic lens

Our eyeglass frame is important for appearance and comfort purpose; however, your eyeglass lenses should not only be trendy, but they must be comfortable offering correct vision and safety for long-term use.

A common mistake most people make when buying eyeglasses is not spending enough time to enquire about the lens materials, design and lens modeling process.

Eyeglass Lens Materials – Features and Benefits

In earlier days, all eyeglass lenses were made of glass. Although they gave precision, glasses are brittle and heavy to carry. For these reasons, glass lenses are no longer widely used for lens manufacturing.

Thickness of lens depends on its size and frame style. For thinner lenses, choose smaller, round or oval frames.

Plastic Lenses: Lightweight plastic lenses, made of polymer called CR-39 were first introduced in 1947 by the Armorlite Lens Company in California. Because of its light weight, low-cost and outstanding optical qualities, CR-39 plastic is still a widely used material even today!

Polycarbonate Lenses: In early 1970s, Gentex Corporation introduced the first polycarbonate lenses for safety glasses. Polycarbonate is lighter and more impact-resistant than CR-39 plastic, ideal for use in children’s eyewear, safety glasses, and sports eyewear.

Trivex is a newer lightweight eyeglass lens material with similar impact-resistant properties as polycarbonate.

High-index Plastic Lenses: In response to the increasing demand for thinner, lighter eyeglasses, a number of optical manufacturing companies introduced high-index plastic lenses. These lenses are thinner and lighter and have a higher index of refraction.

The index of refraction relatively measures the efficiency of an optical material to refract (bend) light depending on how fast light travels through the material. A lens made of a material with a high refractive index will be thinner than a lens made of a material with a lower refractive index.

Aspheric Design

In addition to choosing a lens material that has a high index of refraction, you should choose an aspheric designed lens. In this lens modeling process, the lens curvature changes gradually from the center of the lens to its edge letting the manufacturers use flatter curves without degrading their optical qualities. Because aspheric lenses are flatter than spherical lens designs, you can have a better appearance and also improved clarity.

Minimum Center Thickness (or Edge Thickness)

The size and shape of your eyeglass frame will also affect the thickness of your lenses, especially if you have a strong prescription. If you choose a smaller, well-centered frame, you can use thinner and light weight lens. Generally, the thinnest lenses are aspheric lenses made of a high-index material.

As far as the design phase of lenses is concerned, one of the critical areas for consideration is minimizing the number of lenses used during optical assembly. Ideally, every lens manufacturing company should use a single lens to reduce multiple aberrations. One of the best types of lenses that can be utilized to achieve this goal is color-corrected aspheric lenses. These lenses reduce both spherical and chromatic aberration making them ideal for a range of applications where quality and accuracy matters.

To note, chromatic aberration occurs in conventional optical lenses when different wavelengths of light focus at different points along the optical axis. The problem is solved by using multiple lenses made of glass that has different directories of refraction into an optical assembly.

However, optics manufacturing companies can use color-corrected aspheric lenses to eliminate chromatic aberration with color-corrected aspheric lenses. The system requires using a few lenses to resolve the issue. Now, many of you might wonder, why the need for reducing the number of lenses in an assembly? Well, the answer lies in the fact that you can considerably reduce the size and weight of the assembly if you use less number of lenses. It simplifies the assembly process resulting in producing imaging lenses that cost much less and outstrip assemblies made of traditional spherical optical constituents.

Knowing Chromatic Aberrations

Optical aberrations are abnormalities not caused by any physical, optical, or mechanical flaws, but they are caused by the lens shape or location of optical elements within a system due to the wave nature of light. There are mainly two types of Chromatic Aberrations - Transverse Chromatic Aberration and Longitudinal Chromatic Aberration.

Transverse Chromatic Aberration occurs when the size of the image changes with wavelength, and Longitudinal Chromatic Aberration happens when different light wavelengths focus at different points along the optical axis because of scattering properties of glass.

Optical designers use different tools to recognize and correct aberrations. These tools often include computer generated spot diagrams and chromatic focal shift comparisons. Spot diagrams represent an assessment of the smallest spot size an optical lens can focus. Chromatic focal shift displays the focal length of an optical lens over different wavelengths.