Physics Of Telescopes: An Introduction To Refracting Telescopes

Refracting Telescopes

Introduction:

A telescope is a device used to magnify distant objects. Telescopes can be used to look at things on earth or at objects in space. The telescopes for use on the earth are known as terrestrial telescopes and the telescopes for looking into space are known as astronomical telescopes.

The refracting telescope is one of many different types of telescope. Refracting telescopes work by refracting the light through an initial convex lens, (known as the objective lens), then through another convex lens (known as the eyepiece lens). These two lenses focus the light into the eyepiece so we can see the image clearly.

What is refraction?

Refraction is a process that occurs when light travels between media of different optical density. Light travels at a speed of roughly 3.0 × 108ms-1 in a vacuum. A vacuum has a refractive index n=1.00. The speed at which the light is travelling will decrease as it moves into differently optically

Due to the nature of a sphere, the light will actually not all be focused exactly towards the focus. Instead, light near the edge of the lens will be focused just before the focal point on the optical axis, and light near the center of the lens will be focused just after the focal point on the optical axis. This produces an image that looks blurry or “out of focus”. The simplest way to prevent spherical aberration is to rather than using a spherical lens, use a parabolic lens. Parabolic lenses have exactly the right shape as to focus the light to a central point. The downside of this is that parabolic lenses are significantly more challenging to make than spherical lenses, so for most cheaper telescopes, other methods are used. Some telescopes eliminate spherical aberration by using two different lenses that have equal, but opposite spherical aberration, so that the aberration cancels itself out and the image appears