User Manual

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TELESCOPE BASICS

MOUNT AND TELESCOPE TYPES

Altazimuth vs. Equatorial (cont.)

These type mounts are good for terrestrial observing and for scanning

the sky at lower power but are not advised for deep sky photography.

Both Altazimuth and Equatorial mounts can track the stars sufficiently

for visual use, however, only equatorials can be used for long exposure

astrophotography. Since Altazimuth mounts are not aligned with the

Earth’s axis, they must use both axes to track an object. With Altazimuth

mounts you will be able to accurately track an object centered in the

field of view, however over time all the other stars in the field will

appear to rotate around the center of the field. This is hardly noticeable

in an eyepiece, but is obvious on film.

Altazimuth Advantages

• Easy to setup and use

• Least expensive type of mount

• Ideal for terrestrial observing

Altazimuth Disadvantages

• Cannot be used for long

exposure photography

• Non-computerized models cannot

track stars and planets

On an Equatorial mounting, the two axes are perpendicular to each

other as they are on an Altazimuth mount. But on an Equatorial

mounting, the left-to-right axis has been tilted so that it is parallel to the

Earth’s axis instead of at the horizon. On an Equatorial mount, only the

axis that is parallel to the Earth’s axis, needs to be rotated. On an

Altazimuth mount, BOTH axes must be moved.

If you would like to do long exposure photography, the telescope must

be mounted on an equatorial mount. Some Celestron telescopes that

are on Altazimuth mountings can be tilted up (with the use of an

equatorial wedge) to orient the azimuth axis parallel to the Earth’s axis.

Equatorial Advantages

• Best for long exposure photography

• Easy to use visually because only one

axis movement compensates for

Earth’s rotation

• Setting circles on non-computerized

models help locate astronomical

objects

Equatorial Disadvantages

• Set-up is more extensive because of polar alignment requirements

• Not suitable for terrestrial use

Do you want a GoTo computerized telescope?

Many Celestron telescopes are computerized “GoTo” telescopes. GoTo

capability is very useful for the novice who needs assistance in finding

objects in the night sky. Since there is a large database of celestial

objects, it is unnecessary to refer to star charts to identify objects.

Once the telescope is properly aligned and an object is selected, the

telescope will automatically “go to” the object. GoTo equipped Celestron

telescopes include both altazimuth and equatorial models. Even without

GoTo, many Celestron equatorial scopes have manual setting circles

that allow you to find objects in the sky with the help of a good

star map.

There are a number of factors to consider when selecting a particular telescope.

These factors will usually depend on your individual requirements including cost,

portability, versatility, usability and appearance. You should also consider how you

plan to use the instrument both now and in the future. Most important, consider

your budget and portability requirements, and select a telescope with the largest

aperture possible.

Types of Telescopes

Refractor Telescope

A refractor telescope uses a lens as the primary. The lens at the front of the

telescope bends the light passing through it until it comes to a single point

called the “focal plane”.

The long, thin tubes of refractor telescopes look much the same as those Galileo

used centuries ago. High quality optical glass and multi-coatings provide today’s

sky watchers views Galileo never dreamed of. The refractor type of telescope is

very popular with individuals who want mechanical simplicity, rugged reliability

and ease of use. Because the focal length is limited by the length of the tube,

refractor telescopes become quite bulky and expensive beyond a four inch

aperture. This limits the light gathering properties of refractor telescopes, but it

is an excellent choice for beginners and those who prefer simple operation and

versatility. Refractor telescopes are also a popular choice because of their

unobstructed view, high contrast and good definition.

Refractor Advantages:

• Easy to set up and use

• Simple and reliable design

• Little or no maintenance

• Excellent for lunar, planetary and binary star observing especially in larger

apertures

• Good for terrestrial viewing

• High contrast images with no secondary mirror or diagonal obstruction

• Color correction is good in achromatic designs and excellent in apochromatic

and fluorite designs

• Sealed optical tube reduces image-degrading air currents and protects optics

• Objective lens is permanently mounted and aligned

Refractor Disadvantages

• More expensive per inch of aperture than Newtonians or Catadioptrics

• Heavier, longer and bulkier than equivalent aperture Newtonians and

Catadioptrics

• The cost and size factors limit the practical maximum size primary to smaller

apertures

• Some color aberration in achromatic designs (doublet)

C8 • Moon • Image courtesy of Sebastian Voltmer