Telescopes - A UBC Math 309 Project - Reflective Telescopes

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Reflector

How Reflector Telescopes Work
The main difference between a refractor and a reflector is the latter telescope involves both refraction and reflection of light rays. Reflector telescopes uses two mirrors (primary and secondary mirror) as well as a glass lens (eyepiece lens) in their lens system. Similar to refractors, light rays are gather through the aperture. However instead of bending the rays through a glass lens immediately, rays are to travel to the back of the telescope where the primary mirror is located. The primary mirror is shaped parabolically so that all incoming parallel rays will reflect off the mirror at their own specific angle and hit the surface of the secondary mirror. Once again a reflection will occur and all the rays will converge to a single point call the focal point. It is from that point where optics of refractors and reflectors are common. Light rays will continue to travel and refracts at the eyepiece lens and forms an image that is magnified to people's perception. However this image is also in reverse to the original image. Refer to the following diagram to understand the components and processes in which light rays travel through a reflector telescope.

Magnification of a reflector telescope mainly depends on the distance of the eyepiece lens with regard to the focal point because the focal length determines how large the image get scale by. Typically a long objective focal length combine with a short focal length of the eyepiece lens will yield greater magnification. However, magnification is not the most important optical property for viewing astronomical phenomenon. The aperture size is more important because it accounts for the amount of light the telescope receives and the more light, the brighter the image. The size of aperture also accounts for the resolution power of the telescope. Larger aperture size will yield high quality of image, more crisp and detail image, and increase clarity of the image.

Advantages/Disadvantages
Advantages of a reflector telescopes

The main advantage is reflector telescope can escape from chromatic aberration because wavelength does not effect reflection.
The primary mirror is very stable because it is located at the back of the telescope and can be support in the back.
More cost effective than refractor of similar size.
Easier to make a high quality mirror than lens because mirror need to only concern with one side of the curvature.

Disadvantages of a reflector telescopes

Optical misalignment can occur quite easily.
Require frequent cleaning because the inside is expose to the atmosphere.
Secondary mirror can cause diffraction of original incoming light rays causing the "christmas star effect" where a bright object have spikes.

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