All about Telescopes
Dutch lensmaker Hans Lippershey is usually credited with inventing the telescope around 1608, but it was Italian physicist Galileo Galilei who first turned it towards the sky in 1609. This first telescope used for astronomy provided an image multiplied by a factor of 3 - enough for Galileo to discover mountains on the Moon, spots on the Sun and countless stars invisible to the naked eye. For over 400 years, the telescope has enjoyed constant technological advancements leading to the wonderful equipment we can use today.
We categorise telescopes into four groups: Refractors, Reflectors, Catadioptric and Dobsonian. Each type of telescope has its own benefits and we have put together a brief overview of them.
Refractors are the traditional type of telescopes that have a lens at the top end and a place where you look through in the other end. This type of telescope has the lens and eyepiece effectively sealing the telescope to avoid letting any dust inside. Typically this makes refractors more robust and tend to be maintenance free. Refractors are also available with very short tubes (such as the Celestron Travelscope) which makes them very portable and great for travelling.
Reflectors use a mirror at the bottom of the tube rather than a lens at the top which means the eyepiece is actually at the upper end and you look sideways into the tube. The reason for this is there is a secondary mirror centrally placed to reflect the light out. So the light enters the tube and goes right the way to the bottom, reflects off the mirror and travels back up the tube and then bounces off a smaller mirror that pushes the light out to the eyepiece. The mirrors can get dirt on them therefore there can be cleaning and maintenance required. Usually you can get a larger reflector £ for £ is comparison to a refractor.
Catadioptric telescopes are mostly Schmidt-Cassegrain or Maksutov optical designs. These use a mirror at the bottom of the tube and a corrector plate at the top along with a secondary mirror in the tube. Sounds a bit messy but this design is very compact and provide high magnifications. They are robust as the have closed tubes and have very high power in comparison to its size.
John Dobson invested this type of telescope mount during the 1960s. Dobsonian mounts tend to be the least expensive but carry the largest aperture telescopes. We have telescopes with over 20" aperture in this form - amazing!
GOTO / Automatic Telescopes
GOTO telescopes are computerised telescopes that are wonderful to use. Typically they have a hand-controller or a Wi-Fi connection that enable you to control where the telescope is aiming. The joy about this type of telescope is the simplicity of navigating the night sky. Once setup, you can select an object from the telescopes internal database (sometimes 40,000+ objects to choose from) including stars, planets and deep-sky objects and the telescope will automatically turn itself and aim at the object and track it in the sky for you. There are refractors, reflectors and catadioptric telescopes available in a GOTO form.