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Parabolic mirrors capture and focus energy, and can distribute it outward. They are a type of paraboloid, used in reflecting telescopes and made with low-expansion glass. They can cause distortion, including coma. They are also used in optical illusion toys and to light the Olympic torch.
A parabolic mirror is a specially shaped object designed to capture energy and focus it on a single point. It can also function as a way to distribute energy from the focal point outward. Parabolic mirrors can also be referred to as parabolic dishes or parabolic reflectors.
Parabolic mirrors are a specific type of paraboloid, known as a paraboloid of revolution. This is a type of elliptical paraboloid that is rotated around its axis and can also be referred to as a circular paraboloid.
One of the first uses of the parabolic mirror was in Isaac Newton’s 17th century reflecting telescope. By using a parabolic mirror, reflecting telescopes correct for some of the aberrations that existed in older refracting telescopes. However, other problems are introduced with the use of parabolic mirrors. This includes a problem called coma, which exists in all telescopes that use parabolic mirrors. Coma causes all objects seen through the telescope that are not in the center of the field of view to appear slightly wedge-shaped. The further out of the field they are, the more distorted they appear.
Parabolic mirrors are usually made with a low-expansion glass, similar to Pyrex glass. The mirrors are kept as fine as possible to reduce image distortion. The processes used to produce high-end parabolic mirrors can take months and cost thousands of dollars.
In addition to amateur telescopes, many people have interacted with a parabolic mirror in the form of a popular optical illusion toy. This small pan has two parabolic mirrors attached to each other and a hole in the top to allow for a small object to be placed. When an object is placed between the two parabolic mirrors, it appears that the object is actually resting in the air a few inches above where it actually is.
During the World Olympics, the flame used for the Olympic torch is lit via a large parabolic mirror. This parabolic mirror collects ambient sunlight and focuses it to an intensity sufficient to ignite the flashlight material.
A most likely apocryphal tradition has it that parabolic mirrors were used in the past as a way to gather sunlight to spontaneously ignite enemy ships, or to heat the enemy’s armor to the point where they were forced to remove it.
