Optical Telescope Overview

To beginner stargazers, picking out the right telescope can be difficult. There are many telescope types to choose from, and it can be overwhelming trying to figure out the classification of the most popular telescopes. The best place to start is with the optical telescope.

Visible Light

All objects with a temperature over absolute zero emit electromagnetic radiation, which refers to the spectrum of waves that carry electromagnetic radiant energy through the electromagnetic field. Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays are all electromagnetic waves.

Visible light is the most obvious type of electromagnetic radiation. It falls between infrared and ultraviolet on the electromagnetic spectrum. Unlike the two waves surrounding it, visible light is seen with the human eye. In fact, it is the visible light that you see when you look around.

Optical telescopes specifically work with visible light, and they are the oldest form of telescope. They will not be able to detect ultraviolet or infrared light; both of which require special telescopes.

How Optical Telescopes Work

The most common telescopes are optical telescopes, especially telescopes used by amateurs or beginners. To put it simply, optical telescopes gather and then focuses light by using lenses, mirrors, or both. The focusing of this light can be used to create a magnified image, take a picture, or collect data.

Since the optical telescope is a broad category of telescope, there are three primary types of optical scopes:

  • Refractors, which use lenses
  • Reflectors, which use mirrors
  • Catadioptric telescopes, which use both lenses and mirrors
  • Characteristics

    Optical telescopes have specific characteristics that relate to their performance. The most important characteristics to know are the focal length, magnification, and field of view.

    The focal length of an optical scope measures how strongly the scope converges or diverges light. Typically, this is measured by the distance that the rays must be brought into focus. Generally, a shorter focal length is stronger because they bring the rays to a focus in a shorter distance.

    The magnification is how much larger a telescope can make an object appear while limiting the field of view. Magnification does not always correlate to the performance or strength of a telescope since magnification reduces the quality of the image. It is important to choose a correct magnification for your optical scope depending on the objects you want to observe.

    The field of view is how much you can see at one point through the instrument. Depending on the object you want to observe, you may want a larger or smaller field of view. Typically, the higher the magnification, the smaller the field of view.


    Whenever you’re using an optical telescope, there will be some kind of distortion to the image. This distortion is called aberrations. In total, there are six main optical aberrations: spherical aberration, coma, astigmatism, curvature of field, distortion, and longitudinal chromatic aberration.

    The reason that aberrations appear is that light disperses or separates whenever it passes through a prism or lens. Different lens types will create different types of aberrations.

    It is important to know about the aberration your telescope produces since the aberration can distort measurements or observations if they are not taken into consideration. So, it is important to research the type of aberration your optical scope produces.