How to choose a good telescope, 5 Easy Steps!

(Last Updated On: March 18, 2018)

When we are new to the field of astronomy first thing which comes to our mind is to buy a telescope, then after researching over the internet, nearest shops, from friends we encounter a lot of confusing terms like aperture, focal length, magnification, reflector, refractor etc. We get really demotivated with these terms and starts to reconsider the decision of buying the telescope. But don’t worry I am here to help you in choosing you your right telescope and removing all of your confusion with my 5 easy steps guide.

Aperture

Most important feature in deciding your telescope is aperture. It is mainly the diameter of lens or mirror used in a device which decides the amount of light to enter in your telescope, bigger aperture means more light which will eventually result in better and clearer picture.

Now you will think of buying biggest aperture telescope that’s fit in your budget but no, there is one drawback also with a big aperture, the size of your device also gets heavy and bulky which will be a big issue for you to carry the device away from the city where you can enjoy night sky with your family. In that case, I will recommend you compact(with less aperture) yet powerful telescope. But if you intend to use it on your terrace or in your backyard then I will recommend the biggest aperture telescope available in your budget.

Magnification and Eyepiece

Second important aspect is magnification or power of telescope which is decided by the quality of eyepiece attached to it. The good thing is it is user replaceable so it is up to us to decide what amount of magnification we want for our device. So you will think “why not use the largest magnification?” but the answer is no, suppose you have a 4-inch telescope and you are using 800x magnification the result will be blurred image. Let me give you an example, you must have a smartphone now at night try to full zoom then click the image you will notice the image is blurred and this happens due to the aperture of the camera in your smartphone. Less aperture causes less light to enter which cause poor quality after magnification. Same thing happens with a telescope.

So, How to decide the right magnification? Simple, you just need to multiply your aperture by 50 if it is denoted in an inch or just multiply by 2 if it is in mm. ex: – suppose the aperture of your telescope is 4inch(100mm) then resulted magnification will be (4inchx50) or (100mmx2)=200x. So now we will buy the eyepiece having a maximum magnification of 200x.

Types of telescope

a) Refracting telescope(Refractors)

There is basically three type of telescope.The first type of telescope is refracting telescope. In this telescope, we use a lens to form an image. This work on a very basic principal, light enters the tube and falls on the lens which focuses the image in the back where the eyepiece is situated.

Advantages:-refractor

  •   It has a very simple design that’s why is very easy to use.
  •   Good for terrestrial use, viewing the moon, Saturn rings, different planets etc. in simple words we can say it is a good substitute for high-end binoculars.
  •  Lens are fitted into a sealed tube so it’s very difficult for dust particle to enter into the tube that’s why it has low maintenance cost.

Disadvantages:-

  • Generally, it has small aperture because making big lenses are bit difficult. So it is costly in comparison with Reflector telescope.
  • It has a long tube which is why the device is bit heavier and bulkier due to this it is a bit difficult to carry the telescope from one place to another.
  •  Sometimes it causes chromatic aberration( In simple terms, we all know that light has different wavelength and when light passes through lens sometimes lens is unable to capture the different wavelengths of light which result in some type of rainbow effect at the side of the lens, this phenomenon is called chromatic aberration).

 

b) Reflecting telescope

In this type of telescope mirrors are used to form the image. Light enters the tube through the primary mirror then focuses the light to a secondary mirror which deflects the light to the eyepiece.

Advantages:-

  • Manufacture big mirrors are less expensive then lens that’s why it has large aperture due to which it is a bit easier to view distant galaxies, nebula, stars etc.
  •  It is cheaper than refracting telescope having same aperture.

Disadvantages:-

  • The tube is not sealed due to which there is a chance of dust entering the tube which eventually results in high maintenance costs.
  •  Not suitable for terrestrial viewing.
  •  Need to collimate the mirrors before using.

 

c) Catadioptric/Cassegrain telescope

In this type of telescope, a combination of both lens and mirrors are used to form the image that is why it has both the advantages of reflecting and refracting telescope.

Advantages:-

  • It is compact in size
  • It has sealed tube which prohibits dust particles to enter into the tube so it has low maintenance cost
  • Good for both terrestrial viewing and for observing deep galaxies.
  • It is best for astrophotography because we can attach a wide variety of accessories to it.

Disadvantage:-

These type of telescope is a bit costlier than Reflector Telescope.

Telescope Mount

To provide the stability to our device a mount is must for device. There are basically two types of mount present:-

(i) Alt-azimuth mount→It is a basic mount which helps to move the optics in up and down and side to side directions. Due to its simple design, it is very cheap and good for beginners to use.

(ii) Equatorial Mount→An equatorial mount possesses two axes and also they are tilted which allows the device to aligned the device with earth’s rotational axis. These type of mount is very good for astrophotography and for more advanced use.

Budget

Another important aspect which we should keep in mind before buying a telescope is the budget. One thing you should also remember that buying a good quality telescope the first time (even if it is little bit expensive) is better than again upgrading or buying the different telescope after a year. But don’t worry about that, in this website I will recommend the best telescope for you in every different budget categories.

 

 

Some useful links:-

Best Telescope Review

Best Books for Astronomy

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5 Replies to “How to choose a good telescope, 5 Easy Steps!”

  1. Hi Vishal. Thank you for the article. I also love astronomy. Like you, at a young age, I had a book about planets. I was always amazed at all of them. Recently, here in Doha, there is a group called Waqif Scope whom I met. They stationed a big telescope in one of the popular souqs (market) here and they allow people to view the moon. I was lucky to have been at the right place and at a right time. For the first time in my life, I finally saw the craters of the moon. I was astounded. Nways, I really like how you detailed the different kinds of telescope. Before that, I thought all were built the same way. It’s just that the more expensive, the better you will see from afar. Now, I know more. Thanks for this. Will bookmark your site and will read more. Thanks again =)

  2. I love to see the stars through a good telescope and especially Saturn with its visible ring and I loved the detail in your article and will use it to make sure my next telescope is a good one, thank you

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