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What is a Parabolic Mirror?

Isaac Newton used a parabolic mirror in a reflecting telescope.
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  • Written By: Brendan McGuigan
  • Edited By: Niki Foster
  • Last Modified Date: 28 July 2014
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A parabolic mirror is a specially shaped object designed to capture energy and focus it to a single point. It may also work as a way of distributing energy from the focus point back outwards. Parabolic mirrors may 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 may also be referred to as a circular paraboloid.

One of the earliest uses of the parabolic mirror was in Isaac Newton's reflecting telescope of the 17th century. By using a parabolic mirror, reflecting telescopes correct some of the aberrations which existed in older refracting telescopes. With the use of parabolic mirrors, however, some other problems are introduced. This includes a problem called coma, which exists in all telescopes using parabolic mirrors. Coma causes any objects viewed through the telescope which are not at the center of the field of vision to look slightly wedge-shaped. The further outside the field they are, the more distorted they appear.

Parabolic mirrors are usually made of a low expansion glass, similar to Pyrex glasses. The mirrors are kept as fine as possible to reduce distortion in the image. The processes used to produce extremely high-end parabolic mirrors can take months and cost thousands of dollars.

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Aside from amateur telescopes, many people have interacted with a parabolic mirror in the form of a popular optical illusion toy. This small pans has two parabolic mirrors attached to one another and a hole in the top to allow placement of a small object. When an object is placed between the two parabolic mirrors, it appears that the object is in fact 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 using a large parabolic mirror. This parabolic mirror collects ambient sunlight and focuses it to an intensity sufficient to ignite the torch material.

A most likely apocryphal tradition has it that parabolic mirrors have been used in the past as a way of gathering sunlight to spontaneously ignite enemy ships, or to heat up the armor of the enemy to a point where they were forced to remove it.

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Discuss this Article

Charred
Post 4

Parabolic mirrors are amazing. They are one of the major design components in the Hubble telescope which enable it to capture light from distant galaxies. The parabolic mirror reflector captures the light then focuses it onto a convex lens and then directs it into an eyepiece.

This results in the breathtaking images you've seen of the death and birth of stars. Without the parabola, I don't think it would be possible.

nony
Post 3

@David09 - Yeah, that parabolic effect works great for sound. You can buy parabolic mirror attachments for your shotgun microphone that will magnify sound at a distance, so you can hear the faint chirps of birds hundreds of yards away, or for more sinister purposes, distant human conversations.

If you don't want to buy them, you can make mirror attachments yourself. I’ve seen some plans on the Internet where you can build a parabolic mirror using things like clear plastic umbrellas for the parabola.

David09
Post 2

I remember taking my son to a science activity center where I live and doing that experiment with the parabolic dish mirror described here. It’s amazing when you see it for yourself. The object actually does look like it is right in front of you. I guess this is the parabolic telescope mirror effect.

They also had some hands on exhibits where they used parabolic dishes to magnify sound in the same way that they magnified visuals. I would stand in front of one mirror, whisper, and my son would hear my faint whisper from the other mirror a few yards out.

paitken
Post 1

Is possible to use a primary and secondary parabolic mirror to magnify the reflected light and see objects at night?

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