When light passes through a spherical lens, it produces a blurry image. That is because of spherical aberration. Spherical aberration is the optical problem that occurs when parallel rays of light pass through a sphere, or a lens that is part of a sphere. Since each ray of light is passing through a different part of the spherical lens, they are each refracted a different amount.
Light passing through the center of a sphere focuses on a point farther away than light passing through the edges of a sphere, and thus all of the light does not converge on a single focal point. This leads to a blurry image. Whether in photography, astronomy, medicine, or research equipment, spherical aberration is a problem that must be solved to create a crisp, clear image.
A look at early astronomy illustrates how spherical aberration led to devices becoming larger and more complicated. Early astronomers were aware of the problem of spherical aberration. They knew that in order to get a clear image of the things they were looking at in space, they would need the light from space to pass through a lens that would reduce spherical aberration as much as possible.
Since they did not have the tools to create lenses that were not spherical, they focused their attention on creating lenses that had less curve to their shape. They also used series' of mirrors inside of their telescopes to correct for spherical aberration. As astronomers worked to correct aberration, telescopes got longer, heavier, and more and more complicated to produce. A better solution was needed for the problem of spherical aberration, not just for astronomers but also for photographers, researchers, and anyone else bending light through a lens.
Modern technology has allowed mankind to create lenses that are not a cross-section of a sphere. These lenses, known as aspheric lenses, are manufactured in many different shapes and sizes. They can be manufactured for ultraviolet, infrared, or visible light.
These lenses and have opened up new and exciting possibilities in every field that uses lenses, including photography, optometry, medical equipment, diagnostic medicine, astronomy, R&D, and defense. Aspheric lenses can reduce the size and weight of any system or piece of machinery while eliminating aberration. Aspheric lenses eliminate distortion caused by spherical aberration, without adding more lenses (the way early astronomers did) that can make your device heavier and more cumbersome.
If you are developing equipment that requires precision focus of light passing through a lens, an aspheric lens will likely be your best solution, and modern manufacturing means that you will be able to get the lens in exactly the size and material that your device requires. For more information, check out companies such as R. Mathews Optical Works, Inc.