Refractor Telescope : Build Yourself

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REFRACTOR TELESCOPE

A refractor telescope, also known as a dioptric telescope, is a type of optical telescope that uses a lens as its primary focusing mechanism. Invented in the early 17th century by Hans Lippershey, and later improved by Galileo Galilei, refractor telescopes have played a crucial role in the development of astronomy. This article will explain the working principles of a refractor telescope, its components, and its applications.

Basic Principles of Refraction

To understand how a refractor telescope works, it is essential to grasp the basic principles of refraction. Refraction is the bending of light as it passes from one medium to another with different densities. This bending occurs because light travels at different speeds in different materials. When light enters a denser medium, it slows down and bends toward the normal line (an imaginary line perpendicular to the surface of the medium). Conversely, when light exits a denser medium into a less dense one, it speeds up and bends away from the normal line.

Key Components of a Refractor Telescope

A refractor telescope consists of several key components:

  1. Objective Lens: The primary lens at the front of the telescope, responsible for gathering and focusing light.
  2. Eyepiece: A secondary lens or system of lenses that magnifies the image formed by the objective lens.
  3. Tube: A long, narrow structure that holds the objective lens and eyepiece in alignment.
  4. Focuser: A mechanism that allows the eyepiece to be moved closer to or further from the objective lens to achieve a sharp focus.
  5. Mount: A structure that supports the telescope and allows it to be aimed at different portions of the sky.

How a Refractor Telescope Works

  1. Light Collection: Light from a distant object, such as a star or planet, enters the telescope through the objective lens. The objective lens is typically a convex lens, meaning it is thicker in the middle than at the edges. This shape allows the lens to bend (refract) the incoming parallel light rays and converge them to a focal point.

  2. Formation of an Image: The objective lens focuses the light rays to form a real, inverted image at the focal plane. The distance from the objective lens to the focal plane is known as the focal length.

  3. Magnification: The eyepiece, located at the focal plane, magnifies the real image formed by the objective lens. The eyepiece lens is designed to take the converging light rays and spread them out again, making the image appear larger to the observer. The magnification of the telescope is determined by the ratio of the focal length of the objective lens to the focal length of the eyepiece.

  4. Focusing: To achieve a clear and sharp image, the focuser is used to adjust the distance between the eyepiece and the objective lens. By moving the eyepiece closer or further away from the focal plane, the observer can bring the image into focus.

Advantages and Disadvantages

Advantages:

  • Simplicity and Durability: Refractor telescopes have a simple design with few optical elements, making them more robust and less prone to misalignment compared to other types of telescopes.
  • Sharp and High-Contrast Images: The use of lenses instead of mirrors reduces light scattering and diffraction, resulting in sharper and higher-contrast images.
  • Low Maintenance: The sealed tube design protects the internal optics from dust and debris, reducing the need for frequent cleaning and maintenance.

Disadvantages:

  • Chromatic Aberration: One of the primary drawbacks of refractor telescopes is chromatic aberration, a phenomenon where different colors of light are refracted by different amounts, leading to color fringing around bright objects. This can be mitigated by using compound lenses made of different types of glass or by employing apochromatic lenses.
  • Size and Weight: Large objective lenses can be heavy and expensive to produce, making large refractor telescopes cumbersome and costly.
  • Limited Aperture: Due to practical limitations in lens manufacturing, refractor telescopes typically have smaller apertures compared to reflectors, which can limit their light-gathering ability and resolution.

 BUILD YOUR OWN REFRACTOR TELESCOPE

You can buy these items and  join us in our workshop where we will help you assemble your telescope and teach how to use it . 

Larger the size of the objective lens more the amount of light that enters the telescope, thus more the resolution. However, with increasing size the cost also increases.

Buy Here: 
60mm : https://amzn.to/3XJ66cr  (This contains all the main parts so no need to buy any other parts)
50mm : https://amzn.to/4ckd2Bz  (This contains all the main parts so no need to buy any other parts)

You can obtain the magnification of the telescope by dividing the focal length of the main lens by the focal length of the eye-piece. Depending on how small the focal length of the eye piece is greater magnification can be achieved.

Buy Here:

25mm and 10mm : https://amzn.to/3ziWM4W (If you have bought the above kit it already contains those)


The diagonal and the focuser are the same for any eye-piece or objective that you buy however the size of the lens holder differs so make sure you buy the correct one according to the objective lens you bought.
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For 50mm : https://amzn.to/4clXoWe (If you have bought the above kit it already contains those)

Once you have the optical tube cut, you need to spray paint it one the inside with black plaint. The black paint absorbs any stray light and allows us for a better view of the object in focus.


The whole telescope will be mounted on a tripod.
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Two things that aren't listed here are the tube holder and the tube itself. These have to be custom built.

MISC ITEMS :

One of the main things one does with a telescope is to click astrophotographs, thus a mobile phone holder is a must.
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The sun cannot be observed directly with a telescope as the highly concentrated light would blind you thus a solar filter has to be installed before observation.
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