Telescope Optics Explained

The telescope and its lenses – information simplified.

Telescopes are optical equipment that captures visible electromagnetic radiation (what we call “light”) that bounces off distant objects.

The lenses in telescopes produce pictures by a process known as refraction, in which the lens bends and focuses light from space, allowing us to see what we’re looking at more clearly.


Lenses are constructed of either glass or plastic.

Glass lenses are preferable, yet even the largest telescopes in the world may bend due to gravity (nothing the average person has to worry about).

Plastic lenses are less expensive but of lower quality, and they distort at high temperatures, hence they are mostly used in toy and novice telescopes.

Lens Types Found In The Average Telescope

Convex and concave lenses are used in Galilean telescopes (telescopes that are straight and do not include a mirror).

The lens is constructed of a specific form of glass called “optical glass,” which has been machine-sculpted into a concave or convex shape.

Convex lenses collect parallel light rays from a distance and bend them to a single point (typically the concave lens) known as the focal point.

Concave lenses function similarly, except that the focus point is now your eye. The focal length of the converging lens determines the strength of bent light.

The objective lens is closest to the thing being seen, while the eyepiece lens is closest to the observer’s eye.

Although scientists have created this apparently easy method of detecting faraway objects by arranging lenses over time, various restrictions prevent exact observations. Lenses, for example, distort light rays (chromatic aberration), glass lenses absorb some light, and huge lenses impair picture quality owing to drooping from self-weight. To create crisp views when using refracting telescopes, supplementary lenses known as refining lenses are frequently put before objective lenses with size considered in to minimize sagging and distortion.


The eyepiece lens is an essential component of the telescope because even if everything else on the telescope is of the best quality if you aren’t using a quality eyepiece, you may as well not have a telescope at all since you won’t be able to see anything.

When a cheap eyepiece is replaced with a high-quality one, telescope owners are sometimes shocked by the difference in clarity.

Magnification/Focal Length

Every telescope and eyepiece has a focal length, which is the distance from the main lens to the point where the picture of what you’re looking at is formed. You can generally find the number for it on the side of your instrument and it is normally in the 400-mm to 3000 mm range (for the eyepiece usually 25 mm to 10 mm). The higher the number, the greater the magnification of your telescope, enabling you to view more distant things.

Two Basic Tуреѕ Of Telescopes

There are several varieties of telescopes for sale. However, these various tеlесоре fall mostly into two types. The first of these two varieties are refracting telescopes, which appear like spyglasses or what you’d expect a telescope to look like. The other kind of reflecting telescope is the larger, thicker one that looks like thick cylinders.

Both refracting and reflecting tеlесоре have advantages and disadvantages. The major emphasis here is on your specific requirements, and as you read this article, you will discover which kind of telescope best suits your demands for backyard astronomy.

  • Infоrmаtіоn Abоut Rеfrасting Telescopes

The design of the refracting telescope is essentially the same as that of binoculars, however, they are on par!

How a refracting telescope works:

  1. At the front of the optical tube assembly, light enters the Objective lens.
  2. The light is directed directly into the lens of the telescope’s eyepiece at the rear.
  3. Finally, the light reaches the eye, revealing an image such as Saturn or the Moon.

A good refractor telescope is one that is totally enclosed. The simple design allows it to be maintenance-free for a number of years. Furthermore, the uncomplicated design makes it safe and simple to use, making it ideal for youngsters.

The Celestron 21061 Aeromaster is, in my view, the greatest refracting telescope that can currently be purchased on the market.

Because of its low price, this refracting telescope is my top pick above the majority of its competitors. You see, normally a refracting telescope will have its eyepiece aligned with the lens at the end of the scope (which can be pretty awkward if you are trying to look at different things), but this one has an eyepiece that you can look into simply by leaning over. It definitely has the most sturdy design of any refracting telescope that I’ve ever used. What I like the most about it is actually its eyepiece.

  • Information About Reflecting Tеlеѕсореѕ

How reflected television works:

  1. The optical tube assembly is illuminated.
  2. The light then travels to the rear of the telescope, where it collides with a large mirror.
  3. The light is then reflected back up the tube by this mirror.
  4. The light then reaches a secondary mirror at the top of the telescope.
  5. The light enters the lens after bouncing off the secondary mirror and ultimately reaching the eye.

Reflector telescopes are fantastic because they have a good price-to-performance ratio. Reflecting telescopes are substantially larger in diameter than refracting telescopes and can collect a lot more light, resulting in far superior views (check out my article on the function of a telescope for more information on this work).

If you want to buy a refracting telescope, you should read my in-depth evaluation of the Celestron Nexstar 8 SE, which is the finest reflecting telescope on the market today. Its onboard computer assists you in locating constellations, stars, and planets, and it even takes your telescope to them using its “tour” function.

Comparing Rеfrасting Telescopes To Reflecting Telescopes

Recognize that reflecting televisions are not cheap. When compared to refracting telescopes, they are normally more costly for greater performance, but if you are buying for a youngster or someone who is just beginning out in astronomy, a refracting telescope would be a better option.

Getting a reflecting telescope is the greatest way to see the planets and other celestial objects. Though you may be able to get similar performance with a refracting telescope, you would need to make a much larger investment, which makes one wonder, “couldn’t the same amount of money be better spent purchasing a more powerful rеflесting telescope?”

Learning how tеlесоре work and understanding the many types of tеlесоре not only make аtrоnоmу intriguing, but tеlесоре themselves offer a new way of looking at the cosmos and call attention to the beauty of other things far away in the universe. If we can see and discover what is beyond the limits of human sight, the secrets of the intergalactic emptiness will be revealed.

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