Choosing your first telescope
When you’re just starting out your hobby different gear and their uses can be confusing, in previous article we looked into different mounts. In this article we will discuss various types of telescopes to help you choose the right one for you. Lets get started!
Refracting telescopes typically consist of lens or a lens group that focuses light to the back of the telescope. Refractors with single lens are called achromats, two lens designs are called doublets and three lens designs are called - you guessed it - triplets. The difference in these is how well the scope is colour corrected.
When looking through a simple achromatic refractor one can see that bright stars and planets have a purple colour fringe around the object. This happens as blue wavelengths of light are slightly out-of-focus. Adding another element corrects this effect to some extent but for best results you want a triplet or even a quadruplet refractor. As you add more lenses the telescopes get naturally more expensive so it’s a balancing act between budget and quality but for a small starter scope refractors are a great way to get into the hobby. These scopes are lightweight and generally have a wide field of view that makes searching your target easier. They are also an excellent choice for astrophotography and do not require any adjustments to the optical components, just grab and go!
Another beginner-friendly scope design is Newtonian reflector. These scopes use a concave primary mirror that focuses light to a secondary mirror which bends the light beam out to the side of the scope to the eyepiece or camera. Still relatively lightweight, these scopes offer the best aperture to money ratio you can get and are almost completely free of colour fringing. Only causes for it can be your eyepiece or corrector but the scope itself focuses all wavelengths of light to the same spot. With some considerations they are also a great choice for astrophotography.
The downside of Newtonians is that they need sometimes some adjustments to make sure mirrors are aligned properly. This is called collimation and the goal is to align all mirrors correctly relative to your eyepiece / camera. It might sound difficult or even intimidating at first but don’t worry - once you get proper collimation tools it’s easy and takes only few minutes to get it right. Practice makes perfect!
If you’re looking to get a good look at lunar craters or planets in our solar system Schmidt–Cassegrain telescope is a great choice for you. These scopes combine high magnification with relatively small size and good colour correction. They can be also used for astrophotography with a corrector lens. Some models even offer a completely corrected field without any correctors. These scopes need to be collimated too but it’s not harder than Newtonians so they are beginner friendly. Most models offer an adjustable focuser tube and secondary mirror as the primary stays in fixed in the optical tube.
For those looking to get into astrophotography and are especially interested in smaller objects like galaxies or planetary nebulae a Ritchey–Chrétien telescope is an excellent choice. This specialized variant of classical Cassegrain uses a hyperbolic primary and secondary mirrors designed to eliminate off-axis optical errors like coma. Large central obstruction caused by the secondary mirror makes these scopes more suitable for imaging than visual as it lowers contrast slightly but compared to a more traditional reflecting telescope configurations Ritchey–Chrétien’s offer larger corrected field and more stable collimation than various other telescope designs.
Fun fact: The Hubble Space telescope is based on this optical design!