Types of Telescopes and Mounts

Types of Telescopes

Telescopes come in all shapes, sizes, and functions. There is a telescope type for each and every band of electromagnetic radiation from gamma rays to light to radio. However, the optical types are all you need. Optical telescopes may only work for visible light, but will let you see just about everything nature has to offer. There are three types of optical telescopes on the market and each has its own advantages and disadvantages.


Refractor Telescope	Reflector Telescope	Catadioptric Telescope (Also known as Cassegrain)
Refractor Telescopes are the original, earliest type of telescopes. Basically just a long tube with lenses on the ends, these small telescopes gather and concentrate light by passing the light through the common focal point of the two lenses. They are relatively cheap and offer the best bang for your buck. Refractors give you clear, detailed, and highly magnified images, and there is no obstruction to block any of the light.	Reflector Telescopes use mirrors instead of lenses to gather light and produce clear and magnified images. A large concave mirror focuses the light, and a much smaller secondary mirror redirects the light into the eyepiece. With all their main optical equipment on one end, reflectors can get quite large. Dobsonian telescopes fall under reflector telescope (Newtonian treflector).	Cassegrain Telescopes are the best of both worlds. They combine a lens (like a refractor) with two mirrors. They are a bit fancier in design and are usually more compact the other two. They are, however also the most expensive. In spite their high costs, these are the most popular scopes on the market.
Pros Easy to use Durable - Requires little or no maintenance Excellent viewing of the moon, planets, and stars. Bright and high contrast images Cons Heavier and longer Cost limits their size and aperture Prone to chromatic aberration (colour fringes and distortions)	Pros No (or minimal) chromatic aberration Can have really large apertures Cheaper to make than refractors Excellent for deep sky viewing They work even if their mirrors are slightly dusty. Cons Not as durable High maintenance – needs frequent cleaning and adjustments Secondary mirror and its supports can get in the way and can create the Christmas star effect Prone to coma aberration - stars will appear to have	Pros Best multi-function telescopes – can be used for the moon, planets, stars and deep sky objects Easy to use and portable Durable shorter tubes Versatile and great for astrophotography Cons They don’t look like telescopes and can confuse people Most expensive telescopes on the market
$Celestron Astromaster 70AZ Refractor$
Celestron Astromaster 70AZ Refractor Telescope	Saxon F767AZ Newtonian Reflector Telescope	Celestron NexStar 4 SE Computerised Cassegrain Telescope

What are apertures and focal lengths?

The aperture and focal length are the two main features of a telescope.

Aperture

It is the width of a telescope’s main optics and it is directly proportional to how much light the scope can gather. It is the primary feature and determines the maximum magnification and brightness offered by the telescope.

Focal length

It is the distance between a telescopes primary optics and its focal point. It works with the focal length of your eyepiece to produce your desired magnification. In many cases you will get the telescope’s focal ratio instead. This is just the ratio between the focal length of the telescope and its aperture.

Telescope Mounts Explained

There are two types of telescope mounts. The AZ (Alt-Azimuth) and the EQ (Equatorial) mounts. You might notice that


Alt-azimuth Mounts Alt-azimuth mounts (AZ) are the simplest of the four types of mounts. They are two-axil mounts allowing you to position your telescope up and down (altitude) or side to side (azminuth). Altazimuth mounts are perfect for low-power telescopes but are not recommended for deep-sky photography.		Dobsonian Mounts Dobsonian mounts are a special version of the altazimuth mount made for beginners. These mounts are grounded by heavy platforms and designed for large Newtonian reflector telescopes. They are light, affordable, and great for any beginner or junior astronomer.

German Equatorial Mounts Equatorial mounts (EQ) are made to watch the entire night sky and are very popular in astrophotography. They are easy to adjust on the fly and can be powered either manually or electronically. The German version uses counterweights to properly balance the telescope on what is known as the polar axis. Aiming this axis towards Polaris aligns the entire mount with Earth’s rotation.		Fork Equatorial Mounts Telescopes with shorter tubes tend to use fork mounts. These equatorial mounts balance telescopes at their center of mass and therefore do not need counterweights. The telescopes are mounted on two arms connected to a motor. More hybrid than true equatorials, you can switch these mounts between AZ and EQ modes as needed. This makes them the most versatile but also heavier and less portable than any other mount.

Recommendations for Beginners

When starting out, your best bet is to go with the telescope that best satisfies your needs as a hobbyist or beginner astronomer. You don’t need every bell and whistle, and often the simpler the ‘scope the better. Look for telescopes designed for what you want to do and then find the largest aperture you can buy making sure you still have enough to cover the cost of the mount. Usually this will be either a small entry-level refractor or Dobsonian reflector. These types of telescopes are easy to use and require little no setup. They will also help you learn to map the sky. The mount you get should reflect the needs of your telescope and your location.

For a more personal approach, seek out a local astronomy club or one of your astronomer friends. These people will teach and let you test drive their own telescopes while helping you find the best solution for your situation. Give OpticsCentral a call or email us if you need a recommendation.