Telescope | 6 Important parts | Steps to use a Telescope

Parts of a Telescope and Steps to use a Telescope

What are the parts of a telescope?

Parts of a telescope:

The essential parts of a telescope can be divided into six broad sections. The parts of a telescope are as follows

  1. Lenses
  2. Mirrors
  3. Eyepiece
  4. Structural Support
  5. Telescope Tube
  6. Finderscope


Every refracting telescope and some variants of reflecting telescope use at most two lenses. One of the lenses serves as an objective lens and the other as an eyepiece lens. Generally, these are biconcave, i.e., they are curved outwards on both sides. The objective is attached at the end directed towards the sample that is required to be analyzed. The eyepiece is placed at the opposite end of the telescope is of a hand-held variant. However, for larger telescopes, the eyepiece is generally placed on the unit’s side for better access. A mirror is incorporated to reflect the light rays from the objective lens towards the eyepiece lens to make such designs. It’s one of the important parts of a telescope.

An attachable objective lens (parts of a telescope) image source: Xanthous Onyx, Lens Canon EF 50mm f1.4CC BY-SA 3.0


Every reflecting telescope and some large refracting telescope use at most two mirrors. Depending on the design, these mirrors may be spherical, hyperbolic, and parabolic or plane in nature. These telescopes are found in several design variations and sometimes incorporate additional optical elements to enhance image quality or mechanically improve the image position. The primary curved mirror forms the objective, and the secondary mirror is placed at the focus of the first mirror inside the telescope tube. This mirror directs the light rays from the primary to the eyepiece. 

Mirror (parts of a telescope)image source: OpenStaxOpenStax Astronomy refracting and reflecting telescopesCC BY 4.0


The eyepiece forms one of the most important parts of a telescope and enables the user to observe the specific object’s telescopic image. The amount of magnification of a telescope is determined by the ratio of the focal length of the objective lens/mirror divided by that of the eyepiece lens/mirror. The eyepiece is a part of the ocular lens. It averts the ocular lens from the damages that can occur if the lens falls and also enhances the clarity of the view of the lens.

Eyepiece (parts of a telescope). Eyepieces can be detachable or non-detachable based on the telescopic design.
Image source:JastrowClave 25mm eyepieceCC BY 2.5

Structural Support

Generally, high power telescopes are large and cannot be used as a hand-held instrument. Telescopic designs incorporate various stands like tripods to mount the telescope properly. Many modern telescopic mounts allow us to rotate the telescopic axes independently in both the vertical and horizontal planes. The horizontal rotation allows to point directionally or at an azimuthal angle, and the vertical rotation allows to elevate or depress the telescope according to the user’s requirements. The half Piller aids the vertical positioning. Mounting a telescope increases its efficiency and ease of usage.

A telescopic mount .Telescopic mounts are available in several variants. (parts of a telescope)Image source: CC BY-SA 3.0Halfblue at the English language Wikipedia (parts of a telescope)

Telescope Tube

The telescope tube forms the body of the telescope and has the primary mirror. Usually, a telescope tube has a diameter of about 8 inches. The telescope tube helps in improving the focal length setting by adjusting the knob, present below the visual back. 

Telescope tube ( parts of a telescope) . The secondary lies inside the telescope tube Image source: Users Ericd on en.wikipediaTelescopeCC BY-SA 3.0


parts of a telescope

The finderscope is a small telescope attached to the main telescopic tube. It is used to find the estimated location of the object that is to be viewed. The finderscope has a lower magnification and a wider field of view. It’s one of the important parts of a telescope.

Finderscope attached to a telescope tube. (parts of a telescope) Image source: anonymous, Finderscope 50CC BY-SA 3.0

How to use a telescope properly?

Steps to use a Telescope

First, consider the telescope type.

Telescopes have different methods for viewing depending upon the type. There are three basic telescopic types: 

  • A refractor is a telescoping form that involves a long thin tube with an objective lens at front to accumulate and focus light to form an image. Another lens is placed at the eyepiece to invert the image upright. 
  • A reflector is a form of telescope that works on the principle of reflection of light from a combination of curved mirrors (or at times a single mirror) to accumulate and focus light to form an image. These telescopes can be of large sizes and can provide pretty good visibility. However, the front mirror-end tends to condense water, which can be problematic to maintain. These are better suited for astronomical observations (galaxies, star clusters, nebulae, etc.).
  • The Catadioptric telescopes are variants of optical telescopes that form an image by combining specially designed mirrors and lenses. This telescopic design is capable of obtaining a higher degree of error rectification compared to an all-mirror or all-lens telescopic configuration. Due to this, the telescopes are comparably expensive. 

Consider the power abilities of the telescope. 

A common mistake that people make is to assume more power translates to higher resolution and better viewing. This is false. High power reduces the brightness concentration of the image and amplifies the blurriness.

For a telescope, 50-power per inch of aperture is the maximum amount of achievable magnification. If a person has a 6-inch reflector, 300-power is the highest they can reach (in case of a 3-inch reflector, it could be about 150-power). Using a Barlow lens for magnifying too far would provide a blurred image. The image formed by a telescope can be blown up to a certain point only.

Use the finderscope.

The finderscope is generally fixed to the side of the telescope. It displays more portion of the sky than the main scope. If you compare, a 50 power telescope is capable of covering an area about the size of one’s fingernail. At the same time, an 8x finderscope can cover an area around the size of a golf ball. The approximate location of the object to be viewed can be observed in the finderscope first before observing through the main eyepiece. 

Use the mount.

Telescopic mounts can be of two types: equatorial or altazimuth.

  • The altazimuth mount is used for rotating the telescope axis in both horizontal and vertical axes simultaneously. These mounts are easy to operate and move. However, an un-driven altazimuth mount needs to be aligned and adjusted manually after certain time intervals along both axes in order to compensate for the rotation of the Earth, for keeping an object within view.
  • Equatorial mounts comprise a single axis (swing East to West or North to South) and are generally un-driven. But, an equatorial mount with a clock drive usually has a huge size, is less portable, costly, and has comparatively less accessible eyepiece positions.

Learn the tripod. 

For placing the tripod correctly, first, one needs to make sure that the three legs are correctly balanced. If any of the three legs are tilted or placed at unbalanced support, the telescope may fall and be damaged. Generally, it is preferred to place the tripod at a flat, level area.


How to pick the correct spot for viewing through a telescope?

For the best viewing experience, one needs to make sure the area is not very polluted, has firm ground support, and is free of background light glitches. Rural areas with clear skies provide the best viewing experience. In the case of cities, the telescope can be placed on the terrace of a tall building. Driveways, decks, or stairways do not make for an advisable place due to the ground’s constant vibrations.

How to decide which object we should observe on a telescope?

  • Before finalizing an object to observe, one must consider their geographic location, time of the year, season, and temperature. First, one should list out the objects that are more visible from their geographic location and altitude.

Is there any way to observe the telescopic images digitally?

It is possible to capture telescopic images. One of the methods of doing so is called Afocal Telescope Photography. This involves focusing the telescope on an object, aligning the camera lens with the eyepiece, and simply capturing the image formed. This method is well suited for telescopes with larger eyepieces. Another method of capturing telescopic images is Prime Focus Telescope Photography. This involves attaching a T-ring and a T-adapter to your telescope and camera for directly obtaining the image on your camera, eliminating the eyepiece.

What is Barlow lens used for?

Barlow lens is a system of diverging lens that is often used in series with other optical instruments. This series of lens helps in obtaining an increased focal length for a given optical system. Practically, Barlow lens provides a cost effective way to increase the net magnification of the eyepiece. However, at times due to atmospheric instabilities the magnified image formed maybe blurred.

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About Sanchari Chakraborty

I am an eager learner, currently invested in the field of Applied Optics and Photonics. I am also an active member of SPIE (International society for optics and photonics) and OSI(Optical Society of India). My articles are aimed towards bringing quality science research topics to light in a simple yet informative way. Science has been evolving since time immemorial. So, I try my bit to tap into the evolution and present it to the readers.

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