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Choosing a Telescope: Reflectors

There are three main types of telescopes that are available to the video astronomy community: Refractors, Reflectors (newtonians), and Cassegrains. Each have their strengths and weaknesses. This post will focus on Reflectors.

Another common telescope is the reflector or newtonian telescope. The reflector telescope was invented by Sir Issac Newton.

Instead of a glass lens, reflectors have a mirror at the back end of the telescope (called the "primary mirror") and a small mirror near the front of the telescope (called the "secondary mirror"). The secondary mirror sits at an angle of around 45°. The viewing port sticks out the side of the tube near the front of the telescope. Light enters the tube and bounces off the curved Primary Mirror at the back of the telescope which brings the light to a focal point. The light then hits the secondary mirror at the front of the tube, which directs it out the side to the viewing port.



Below is an image of an 8" f/4.9 newtonian telescope. If you look near the top, you can see the viewing port.

Orion Skyview Pro 8" Newtonian

Below is a Skywatcher 12" f/4.9 dobsonian Goto telescope. It's a newtonian telescope as well. The mount is what makes it a "dobsonian". When pointing straight up, it is about 60" tall and weighs about 100 lbs including the mount. Some the biggest dobsonian telescope I've seen had a tube diameter of 42". To look through it, one needs a tall step ladder (because the view port is at the front of the tube).

12" Skywatcher Dobsonian Telescope

#videoastronomy #newtonian #dobsonian


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