9 important things about telescopes that you NEED to know

Telescopes are the instruments used to magnify and observe distant objects. It uses a combination of lenses or curved mirrors to collect the light coming from the distant object. The light coming from a distant object forms a very small image in our eye retina and hence we can’t see it but that can be done by bending and focusing the light using lenses or curved mirrors, telescopes do the same thing.

There are two main elements in the telescope:

The Objective 

The primary optical element in the telescope is an ‘Objective’ which can be a lens or a curved mirror that collects a lot of light and brings it to the point of focus.

The Eyepiece

An eyepiece lens takes the bright light from the focus of the objective lens or a primary mirror and magnifies it and enables us to see the image with comfort to the eye.

Before going into the types of telescope let’s discuss two general properties of the telescope.


The most important aspect of any telescope is its aperture, the diameter of its main optical component, which can be either a lens or a mirror. A scope’s aperture determines both its light-gathering ability (how bright the image appears) and its resolving power (how sharp the image appears). Apertures commonly recommended for beginner telescopes range anywhere from (70 mm to 100mm in refractor) or (5 inches to 10 inches in reflector).

Generally, the larger the aperture, the more the amount of light the telescope collects and brings to focus, and the brighter the final image.

A larger aperture lets you see fainter objects and finer detail than a smaller one can. But a good small scope can still show you plenty if you go far from city lights. 

For example, from a dark location, you can spot dozens of galaxies beyond our own Milky Way through a scope with an aperture of 80/90mm of refractor or a 5 /6-inch reflector. But you’d probably need a bigger telescope to see those same galaxies from a typical suburban area. And regardless of how bright or dark your skies are, the view through a telescope with a larger aperture is more impressive than the view of the same object through a smaller scope. 

Avoid telescopes that are advertised by their magnification, especially implausibly high powers like 600×. For most purposes, a telescope’s maximum useful magnification is 50 times its aperture in inches (or twice its aperture in millimeters). So you’d need a 12-inch-wide scope to get a decent image at 600×. And even then, you’d need to wait for a night when the observing conditions are perfect.


The telescope’s Magnification is its ability to enlarge an image, depending on the combination of lenses used. The eyepiece performs magnification.

Since any magnification can be achieved by almost any telescope by using different eyepieces, Aperture is a more important feature than magnification.

Types of telescopes:

Telescopes are of different types based on what primary objective is used; it can be either a lens or a mirror.

Refractor telescope

Refractor telescope

  • Refractors use glass lenses to focus and magnify the starlight.
  • Sharp, high-contrast views.
  • Great for observing the moon and planets.
  • Can be used for daytime viewing with the correct image accessory.
  • Hardly any maintenance is required.  
Reflector telescopes

Reflector telescope

  • Best price per aperture size.
  • Reflectors use mirrors to collect and focus on starlight.
  • Bright and detailed views of fainter deep sky objects as well as the moon and planets.
  • Excellent all-around performance and value.
  • Some maintenance(collimation) is required periodically.
Cassegrain telescope

Cassegrain telescope

  • Cassegrains use both mirrors and lenses to focus on starlight.
  • Compact size but long focal length, great for high maintenance observing.
  • Very portable and easy to use.
  • Especially good for seeing the planets and the moon.
  • Can be used for daytime viewing with the correct image accessory.
Telescope mounts and their types


You should also decide what type of mount you want to use with the telescope.

The telescope sits on the top of the mount so obviously, the mount is what moves it and follows things in the night sky.

There are two main types:

  1. Altitude-Azimuth mount
  2. Equatorial mount
Alt-Az mounts:

Alt-Az mount

  • An Altazimuth mount or AZ mount provides simple up/down, left/right  OR vertical – horizontal motion control.
  • Alt-Az mounts do not require any alignment but do not track objects as easily as an equatorial mount.

To follow something in the sky where celestial objects move along an arc from east to west direction is difficult using Alt-Az mount as it can only move in up-down and left-right directions. So, to track the celestial object using the Alt-Az mount you will have to move the telescope in a zig-zag pattern, a kind of stair-stepping.

EQ mounts:


Equatorial Mount moves with the earth’s rotation, there is a little more setup involved.

It has two movements – one is the Right ascension which rotates about an axis pointing towards the north star. So it’s a movement in the East-West direction or parallel to the celestial equator or along the celestial longitude and a Declination which is a movement in the North-South direction or along the celestial latitude.

Since the equatorial mount follows the motion of celestial objects in the sky it’s easier to track night sky objects. 

The advantage is once you have found something,  you can lock it down and using the fine adjustment knobs to fine-tune the positioning and control you can twist the RA knob and you can follow the targeted object as it moves through the night sky if it is polar aligned correctly.

  • An equatorial, or EQ mount mimics the Earth’s rotation making it easier to manually track objects across the sky.
  • Equatorial mounts need to be aligned with Polaris before each use to track objects properly.
GO-TO Mounts (computerized mounts)

Go-to 'Alt-Az' mountGo-to 'EQ' mount


Computerized mounts are auto-guided mounts. It comes in both versions – Alt-Az and Equatorial. It is well programmed to guide inbuilt motors for each axis inside the mount and using the remote control one can point the telescope in the desired direction. It consists of the data of all famous catalogues of deep-sky and solar system objects. As you enter the catalogue name or co-ordinate of the object it will automatically point the telescope towards that.  Polar alignment is essential to point the objects correctly and an additional power supply is needed to carry with it.

  • A computerized “Go-to” telescope can locate and track objects in the sky for you.
  • Go-To systems require alignment before each use.
  • If you want to see as much as possible in a short amount of time, consider a motorized Go-To telescope.
  • If you want to enjoy the ‘hunt’ of location objects on your own, consider a manual telescope with an equatorial or Altazimuth mount, or a Dobsonian base.

Still need to know more before deciding on your first telescope? Check out Best telescopes for beginners

Three things to consider when choosing a telescope:
  • Cost – How much do you want to spend?

If you are just getting into it and you’re not sure if it’s going to keep your interest well then you probably don’t want to spend a lot of money but a simple small telescope (60-70mm refractor OR 4/5inch reflector) is very affordable. It can get you into the moon and planets and you can see the craters on the moon. So you don’t have to spend a lot of money to see some nice things in the sky.

  • Aperture (diameter) – The bigger the aperture, the better the view.

The aperture is the most important thing. The bigger the telescope is, the more light it lets in and the more resolution you will get.  Everything’s better with a bigger telescope except for the size.

  • Physical size (portability) – How easy is it to set up and use?

If you go out and buy the biggest thing you can and realize this is way too heavy for you to log in and out and it just sits inside then what good is it as a telescope? So definitely think of the physical size and how much you’re going to be lifting and putting up and setting up every night.

So ask yourself these three questions and then you can narrow it down to some good choices for yourself.

Enjoyed reading this? Join us for our event where you can actually use telescopes to look at deep-sky objects! Starparty at Dehene

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1 Comment

  • Joe
    Posted July 29, 2022 9:12 am 0Likes

    You actually make it seem so easy with your presentation but I find this matter to be actually something which I think I would never understand. It seems too complicated and extremely broad for me. I’m looking forward for your next post, I’ll try to get the hang of it!|

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