Lens AberrationWhat is causing the blurred images?
In the previous article , it explained some characteristics of light and the basics of lenses. Some types of lenses make small objects look bigger while other types of lenses make far-away objects look closer. Different types of lenses are combined in microscopes and cameras so that they project images more accurately and clearly.
In this article, let’s learn about aberration. Aberration is one of the reasons why some apparatuses need a lens constitution of more than one type of lens.
★A Piece of Trivia
The minimum size that a human’s eyes can see is approx. 0.1mm, which is about the thickness of a thin hair. With an optical microscope manufactured by Olympus, you can see bacteria and viruses measuring about 0.2µm (0.0002mm)!
What Happens When Aberration Occurs?
Aberration is a phenomenon when light passing through the lens does not completely converge into a single point. Aberrations cause the image seen through a microscope or taken with a camera to be blurred or distorted. Aberrations fall into roughly two classes: chromatic aberrations that are caused by a variation of color of light, and monochromatic aberrations that could be caused by monochromatic light. In other words, monochromatic aberrations are not affected by colors of light.
Normal light, such as sunbeam, consists of a mixture of different colors. In the previous article “Relationship between light and lens”, it mentioned that “Light is like both a particle and a wave.” Usually, each color of light has a different wavelength. The degree of refraction at the lens varies depending on each wavelength. For example, with a convex lens, yellow light has a bigger refractive angle than red light, whereas blue light has an even bigger refractive angle, resulting in an image that is slightly off focus. Deviations of the focal point arising in this manner is known as chromatic aberration. Chromatic aberrations cause the image to be glazed over or blurred.
One type of “monochromatic aberration” is spherical aberration. The surface of a regular convex lens is like the shape of a part of the surface of a round sphere. Therefore, the farther from the center of the lens the tighter the curve becomes, and thus, the refraction of light becomes tighter as compared to the refraction closer to the center of the lens. This causes a deviation in the focal point known as spherical aberration. Spherical aberrations cause the image to be blurred.
How Can You Eliminate Aberration?
Some products, such as microscopes and cameras that require objects to be seen precisely, need to have as little aberration as possible. Especially, as a microscope is used to magnify minuscule objects, even the smallest deviation is easily noticed. Thus, it is critical to make use of extremely sophisticated technology.
Many cameras and microscopes are designed to offset aberrations by combining convex and concave lenses that have mutually reverse aberrations or by combining lenses with different degrees of refraction. For instance, camera lenses and microscope objective lenses manufactured by Olympus consist of a combination of many different types of lenses.
To minimize aberration, it is crucial to have precise lens design as well as sophisticated manufacturing/processing technology.
★A Piece of Trivia
High-performance microscope objective lenses can be very expensive. A special type of glass is used as the material for the lens, the value of which is almost equivalent to that of diamond!
Other than combining different types of lenses, some lenses are made to minimize aberration in different ways. One such way is to use aspheric lenses. In aspheric lenses, the degrees of curvature are differentiated at areas close to the center and at areas near edge of a lens, in an attempt to generate a single focal point. Aspheric lenses can reduce spherical aberration.
As stated above, precise design of lenses and sophisticated manufacturing technology can offer clearer and more beautiful images.
The Enduring Technology of Lenses That Control Light
Lenses have been used by humans for around 2000 years. The technology of lenses has been applied to various apparatuses and is still continuing to develop. Recently, research and development for numerous novel technologies, including AI (Artificial Intelligence), telecommunication/video equipment, and high-tech products, are progressing in response to changes in our lifestyle. That being said, the technology of lenses that control light shall never die out, but instead, it shall continue to be indispensable in forging our future along with those new technologies. Olympus also contributes to society through our businesses such as microscopes, endoscopes and cameras that utilize lens technology.