What is Extra Low Dispersion (ED) Glass

Extra-low-dispersion glass, also known as ED glass, is widely used in optics applications where clarity of vision and accuracy are important. It's found in high-end camera lenses, binoculars, sights, scopes, rangefinders and countless other devices that depend on precise image quality.

Upland Optics uses ED glass exclusively in all of its products because we know that the added optical clarity is well worth the additional cost.

The physics behind ED glass products are complex. This simple guide will help you gain a solid understanding of what makes ED glass sporting optics so effective.

A Quick Primer on Optics

Light is an electromagnetic waveform. As it travels through media like air, glass or water, its phase velocity changes depending on its frequency. This is known as dispersion.

To simplify this concept, consider the way a prism splits white light into different colors. The original beam that appeared white was actually composed of many waves of colors all corresponding to particular frequencies. Dispersion essentially means that because the different frequency wave crests propagate at unique rates through the prism, they become distinct from one another. It's sort of like how individual swimmers in the same pool start to spread out as they travel at varied speeds. It may also help to remember that dispersion is sometimes referred to as chromatic dispersion because of how it relates to color.

Dispersion and Refraction

Refraction is a phenomenon where light bends due to its propagation velocity changing. In the prism example, the velocity change is induced as the light transitions from traveling through air to traveling through glass. Dispersion acts in conjunction with refraction because the amount of directional change depends on the color of the light.

Dispersion in Optics

So now that we've covered most of the physics, how does chromatic dispersion impact glass, and why is extra-low-dispersion glass necessary? In short, no glass is perfect. Although traditional lenses and other optics are designed to minimize distortion, almost all exhibit some form of chromatic dispersion. In cameras, binoculars and other optics, the phenomenon is commonly known as chromatic aberration, or CA. As we'll discover later, ED lenses are fabricated to minimize CA as much as possible.

The Visible Disadvantages of CA

Because distinct colors refract differently as they traverse optical components, CA often results in lenses being unable to focus multiple hues uniformly. For instance, you might take what you think is a great sports photo only to discover that the edges of objects display rainbow blurs or fringes.

With binoculars and other lenses designed for real-time use, CA isn't just annoying. It can hinder your ability to enjoy your viewing or perform because you're looking at a distorted image. At higher magnification, the fact that light is being refracted at even sharper angles may make the effect even more pronounced.

A Viable Solution

Low-dispersion glass is specifically designed to minimize chromatic dispersion. Traditionally, it was manufactured by combining two glass elements into a single unit called an achromatic lens, or achromatic doublet. If one element had a high dispersion characteristic and the other was accordingly low, they would ideally cancel out. In some applications, manufacturers coated lenses with substances designed to produce similar effects.

Of course, these solutions depend on finding different types of glass, coatings and lens combinations with suitable dispersion effects. In their search, scientists created a host of materials that further pushed the boundaries of what sporting optics could do.

How Is ED Glass Made?

By combining different minerals and manufacturing techniques, scientists created products that minimized CA and produced sharper, brighter images. Modern ED glass fabrication employs tested material choices and precise quality control to create products with specific physical and optical characteristics. Unlike in decades past, manufacturers can use automation techniques and computer control to maintain furnace temperatures, consistent cooling flows and exact substrate mixing for highly consistent results.

The Benefits of Extra-Low-Dispersion Glass

Older achromatic doublets and similar solutions weren't ideal because it's hard to create perfectly matched materials and lens sets. Adding multiple components to objects like binoculars and telephoto lenses can also increase their weight until usage becomes uncomfortable.

Sustainable Improved Usage

ED glass is specifically designed to have minimal CA characteristics inside sporting optics and other devices. One interesting side effect of the manufacturing process that grants ED glass its unique optical qualities is that it's resistant to the temperature changes that had a major impact on prior lens variants. This increases imaging consistency in exposed environments and ensures users can rely on what they see to be accurate.

Many ED glasses are manufactured to produce improved quality over a specific range of colors. As a result, it's much easier for consumers to source purpose-designed optics that fit their intended applications.

In conclusion, ED glass is the way to go when it comes to sporting optics. That's why we build every one of our products with it at the center.