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!
