Choosing Your First Telescope - Telescope fundamentals

For Chennai Astronomy Club by Sabari Nath

I still remember myself as an 8-year-old atop my home gazing at the ocean of stars. Out of those innumerable stars stood an imperfect line of three stars, distinct and bright as ever. Since then I always wanted to spot that star trio. And for some reason, it was rewarding and satisfying to find those specific set of stars – which I later came to know as the Orion Belt. I am ever-curious and my love towards astronomy grew stronger each day. I wondered looking at the ultra-high resolution images of Saturn’s rings and Jupiter’s Redspot. And I happened to glance at Hubble’s image of Pillars of Creation, later to realize that the light from that distant nebula has, in fact, traveled for around 7000 light years to reach Hubble’s delicate sensors. Retrospecting this, we can also suppose that star-gazers are peaking at the glimpse of the past. This was quite a revelation for me.

So it was time, and I decided to plunge into amateur astronomy. I looked for beginner level telescopes and binoculars. With myriad scopes available, I was baffled to choose my weapon of choice. I started to follow the amateur astronomy clubs, Chennai Astronomy Club being one among them. One thing I noticed commonly among these clubs is that the members are approachable and down-to-earth, be it the founder or a new member. I learned about the tools and accessories involved in manifesting a decent astrophotograph. I bought my first telescope, a Celestron Astromaster 130EQ-MD Telescope. Is my decision to buy a telescope right or just another instance of my impulse behavior? Let us find. Also, I hope that my telescope shopping experience will guide you to make an informed decision.

No Telescope Is Bad Telescope:

With the new found passion of amateur astronomy, people tend to rush their cognition in choosing their first telescope. And the good news is that any and all telescope that you can buy is a good telescope – contrary to the popular belief – for it feeds your passion. This said, avoid buying a cheap plastic telescope from your local mall or Amazon. If you are proceeding with such products, avoid having high expectations as the 100x zoom promised in the product description isn’t going to fetch you your desired image. Likewise, do not spend too much on compound telescopes – as it kills the joy of learning the basics.

What are the types?

With several varieties of telescopes available in the market, there are three general types of telescopes.

Refractor Telescopes: The good ol’ telescope model which collects light with the lens at the front of the telescope’s tube.

Reflector Telescopes: To gather light, reflectors use a curved mirror at the back end of the telescope’s main tube. The reflected light is collected by the focuser to create the image.

Compound Telescopes: Compound telescopes(a.k.a catadioptric telescopes) use both lenses and mirrors to gather light. Simply put, it’s a combination of the Refractor and the Reflector.

Ascertain the Fundamentals:

Aperture, Focal Length, Magnification, and f/ratio are the must-know features of any telescope. Before buying a telescope, it is quintessential to comprehend the importance of the above features.

Aperture: The diameter of the primary lens, or mirror, in a telescope is designated as the Aperture. It is not only important for gathering light, but also for seeing detail. Larger the aperture, better the light collection - which means that you can see fainter objects. For starters, do not go any less than 130mm.

Focal Length: Focal length refers to the distance between the primary lens/mirror and the point where the object is brought into focus. Focal length is the major determining factor of any given telescope’s magnifying power. Adding crude magnifications will not help you with rendering a good image.

Magnification: Too much magnification makes for nothing more than a blurry image because telescopes can only gather so much light. Higher magnification means you’re just stretching the same amount of light over a larger area - resulting in useless magnification. The cheap plastic telescope that promised 100x in its cover, technically, can zoom 100 times but lacks resolution.
The theoretical limit of useful magnification for a telescope is 50 times the telescope’s aperture in inches or twice the aperture in millimeters. So, for a 130mm telescope, the maximum useful power is 260 times the magnification of the naked eye. It is at this power that the resolution of the telescope matches the resolution of your eye and this is the point at which the images are the sharpest.

f/ratio: f/ratio is the focal length of the telescope divided by its aperture.

So, for example, my Celestron 130eq telescope is a 130mm aperture reflector with a focal length of 650mm. The f/ratio is thus 650/130 = 5, denoted as “f/5”.

The range f/5 to f/10 is a fairly good one for general purpose telescopes. Telescopes with longer f/ratios perform well and are relatively void of optical distortions known as aberrations. People using short focus refractors experience chromatic aberration which renders false color around brighter objects. Short focus reflectors maintain sharp images in the center of the FOV but have a significant vignetting problem.
So, any aspiring amateur astronomer must understand how a telescope works. Learning the aforementioned features will let you select the telescope best suited for your requirement.

Mount Matters:

A telescope is only as good as its mount. A telescope magnifies the sky, but unfortunately, it also magnifies the minuscule vibrations due to sundry factors.

Altazimuth: Altazimuth is the simplest type of mount with two motions, altitude (vertical) and azimuth (horizontal). Good Altazimuth mounts have knobs for making precise adjustments, aiding smooth tracking across the sky. These mounts can be used for terrestrial observation and are difficult to use for deep sky astrophotography.

Dobsonian Mount: The Dobsonian mount is a modified version of the Altazimuth mount. Dobsonian mounts are mounted on the ground by a heavy platform and designed to support massively sized Newtonian Reflectors.

Equatorial: Equatorial mounts are suitable for astronomical observing over long periods of time and are amazing for astrophotography. As the earth rotates around its axis, the stars appear to move across the sky. Equatorial mount helps in guiding either by manual slow-motion controls or by an electric motor.

Fork Mount: Most Catadioptric hybrid telescopes use this style mount. Fork mount consists of an internal computer which is fully automatic and can guide the scope to the focus on the required object.

Key Takeaway:

Control the adrenaline pumping in you, which forces you to buy a telescope without knowing the basics. First off, a good pair of binoculars makes a very good instrument for a budding amateur astronomer. Getting a telescope isn’t necessarily a prerequisite for being an amateur astronomer. A decent pair of binoculars will serve you just as well - while cutting some slack on your wallet. Give it a thought.

Learn the fundamentals, explore the amateur astronomy community, feel free to approach a pro, realize what type of Astro-gazing you want to get yourself into, calculate the type of equipment needed for you, assess the budget required, consider the available budget, and factoring in all these variables, make an informed decision. Amateur astronomy is a costly affair, nonetheless a rewarding one. Looking at the stars will make you humble and will provide you with an opportunity to learn about the Universe, and in due process, Yourself. To infinity and beyond!


Thanks for the wonderful write up. I am currently using
beginners telescope celestron power seeker 70AZ for more than 5 years. I want to get a good next level telescope. Max i can go till 30k. Any telescope dealer in chennai? do we need to order online only?
I am based of chrompet so we need to consider the city light pollution.


There are no telescope dealers in Chennai. There are two in Maharashtra. At the 30k level, I would suggest getting a dobsonian if you are only into visual astronomy.


Where can i get a telescope in Chennai? . Or ,are there any trusted dealers in here ?

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There are no dealers here. You can check with Tejraj or CSky telescopes who are based out of Maharashtra. I believe they are the two largest dealers who have some physical presence in India. Other than that, you can also buy from Amazon or Flipkart.

Recently an amateur astronomer from Bangalore has also started selling scopes.
You can see it at

Sir what model/series would you recommend for viewing deep space objects and viewing planets such as saturn clearly ?

There is a celestron dealer in Chennai, kolathur, invitty traders

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The best you can go astromaster 130eq

@Thiyagarajan, it really depends on what you want to see.

If the answer is planets, you would have to buy a scope with a long focal ratio(f/8, f/9, f/10, for example). This makes it easy to magnify the planets so that you see it clearly. You also want to get something with enough aperture so that you get to see details on the planets. You will probably need a motorised mount so that the object stays in the field of view even at high magnifications.

If you want to do DSOs, you really need aperture. People usually use lesser magnification than needed for planets and hence you may not need a motorised mount to keep the object in the field of view. Dobsonians are very suitable for this as they give the most aperture for a given budget. You may find it difficult to do planetary observations with this as you will have to keep moving the scope to compensate for the earth’s rotation.

If you want to do astrophotography, a lot more factors come in. For planetary photography, you go for scopes with a long focal ratios and for DSOs you go for short focal ratios.

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I am not sure if you have used and compared the Astromaster with other scopes. I would strongly suggest not buying this scope.

The astromaster comes with a spherical mirror. This leads to something called spherical aberration because the light rays are not focussed to a single point. Please see this image.

Also, the scope comes with a horrible eyepiece out of the box. You will have to spend extra $ to get a new one. The mount is also super flimsy.


So which one is best

@Astrobarath369, there is no single “best telescope”. It depends on a lot of factors:

  • Your interests(planets or DSOs or solar observations)
  • Your ability to carry around heavy gear(an 8 inch dob might be around 30kgs)
  • Your budget
  • You want to do visual or photography

It’s really hard to suggest a telescope without knowing what the answers to these questions are.


Both (visual and photography)

If it’s only for visual, get a dobsonian. You can easily get a 6 inch dob for that price. If you save a few more, you can get an 8 inch also.

However, you cannot do any serious photography with a dob unless you get a tracking platform for it. Even then, you might be restricted to planets only.

The cheapest way to get into astrophotography would be to get a star tracker and use your DSLR with a zoom lens as an alternative to a telescope. Needless to say, you cannot do visual with this setup.


Sir thank you for the response .I have a question, can i get telescopes for rental in chennai ? The reason is I want to get some hands on experience please suggest .

I’m not aware of any telescope rentals here.

Sir can i get your number ?

There is Orion Dealer in Madurai, Go Scientifics. He has a good Collection on Orion Scopes, Ships Nationwide. You can try him too.

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Sir can you give his details and his number ?I am waiting eagerly :weary: :weary: :weary::

Please check out his website, His Contact details are Mentioned in the Website itself. I checked the Orion Website, He is the Orion’s Official Dealer in India.

Happy Stargazing.