Telescope Parts

About Telescope Parts

Many telescopes have parts that are common in name to each other, whilst others depending on the make quality and type may have parts that are not found on other models. Cheaper models of scope will consist of far fewer parts then those mentioned here.

Apart from the main pieces that make up the telescope there are other items such as brackets and screws which you will generally find in the manufacturers manual.

Although not an exhaustive list of telescope parts the following covers the basics.

Optical Tube:

Every telescope also has an optical tube often shortened to 'OTA'. This is simply a hollow tube that can be made from any number of different materials and to which various other telescope parts can attach directly.

Dovetail Plate:

This is a finely machined part that attaches to the telescope body and to the mount. However because many scopes differ in design the dovetail plate is often manufactured specifically for particular models.


A focuser can come in a variety of styles. Essentially, it is an assembly which attaches to the telescope tube and holds the eyepiece. The majority of models have a knob on the side (rack and pinion in the case of a Crayford Focuser. This enables the internal tube to back and forth until focus is achieved, altough there are a number of models (helical) which move left or right..

Tube Rings:

Larger telescopes will have tube rings, these are hinged wrap around the optical tube and fix to the telescope mount with thumb nuts.


Telescope Eyepieces are available in a range of magnifications, common sizes are 1.25" and 2". There are many different options and quality can differ immensely between them.


The finderscope attaches to the main optical tube and is used to locate objects quickly.

Counterbalance Weight:

The counterbalance weight is a simply a weight used on a equatorial mount to balance the weight of the telescope optical tube assembly. Correct balance has to be maintained to prevent wear on gears.

Primary Mirror Cell:

The primary mirror cell is the assembly which holds the primary mirror of a reflector telescope. Again the design also varies from between manufacturers, however the basic principle is the same. It holds the mirror and provides for any adjustments that may be required.

Objective Lens Assembly:

This is the primary light gathering assembly for a refractor telescope. It is basically a collar which holds the primary lens in place and fits onto the telescope tube.

Setting Circles:

Setting circles are an important part of an equatorial mount, and give accurate numerical settings for ascension and declination of sky coordinates. By aligning the numbers with listed coordinates, setting circles are used to assist the observer to locate space objects.

Telescope Mount:

The telescope mount holds the telescope in place. The two common mounts use by amateur astronomers are the alt-azimuth and the equatorial.

Altazimuth Mount:

An Altazimuth or alt-azimuth mount is a simple mount used for moving a telescope along two perpendicular axes of motion, one vertical and one horizontal. The vertical movement is known as the altitude, while the horizontal motion is called the azimuth. offers great deals on altazimuth telescope mounts.

Equatorial Mount:

The equatorial mount uses two axes that are lined up with the poles to keep track of the motion an object takes across the sky. The axes can be Right Ascension, Polar, or Declination. Instead of moving up and down on its axes like the Alt-Azimuth, this particular mount is tilted toward the Earth's axis of rotation.


One of the more essential telescope parts is the tripod which can be made from different materials and is used to support the telescope and all accessories. It is adustable to allow for a convenient viewing height.

Star Diagonal:

A star diagonal is an angled mirror or prism used in telescopes that allows viewing from a direction that is perpendicular to the usual eyepiece axis. It allows more convenient and comfortable viewing when the telescope is pointed at, or near the zenith (i.e. directly overhead).

The resulting image is the right side up, but is reversed from left to right. Star diagonals are available in 1.25" and 2" diameters. The 2" diagonals allow larger longer focal length low power 2 inch barrel eyepieces for a greater field of view.

Barlow Lens:

A Barlow lens is an extra lens that can be placed between the focuser and the eyepiece. It effectively increases the focal length of the telescope, therefore increasing the magnification of a telescope.

Dew Cap:

The Dew Cap keeps out stray light and reduces the tendency for dew to form on the main lens.

Astronomical filters:

Filters work by blocking a specific part of the color spectrum, and significantly enhance the remaining wavelengths. Colored filters work by absorption/transmission, and instantly tell you which part of the spectrum they are reflecting, and therefore transmitting. The so-called light-pollution reduction and nebulae filters are very selective in the wavelengths they transmit.

For further information on telescopes parts the manufacturers manual should be consulted.

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