Telescope Basics; Focusing The Telescope; Calculating Magnification; Determining Field Of View - Celestron StarHopper 10 Instruction Manual

Celestron starhopper 10: instruction manual

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Table Of Contents

Table of Contents

Focusing the Telescope

The Star Hopper

telescope is equipped with a rack and pinion focuser. Focusing is accomplished by

rotating the focuser knobs until a sharp focus is reached. To focus your telescope, begin by putting the

eyepiece in the eyepiece holder of the focuser. When doing astronomical viewing, you'll find that out of

focus star images are very diffuse and difficult to see. Therefore, choose a bright object, like the moon or

a planet for your first astronomical target. This way, the image will be visible even when out of focus. If

you're focusing on a star, its image should, as closely as possible, resemble a pinpoint. If you're focusing

on the moon or a planet, rotate the focuser barrel until the image is sharp.

Calculating Magnification

You can change the viewing power of your Celestron Star Hopper

eyepiece. There are various optional eyepieces shown in the Optional Accessories section of this manual.

To determine the magnification of your telescope, simply divide the focal length of the telescope by the

focal length of the eyepiece being used. In equation format, the formula looks like this:

Magnification =

To determine the magnification using the standard 25mm eyepiece, simply divide the focal length of your

Star Hopper

telescope by the focal length of the eyepiece (25mm). For example, dividing the focal

length of the Star Hopper

power is variable, each telescope, used under average skies, has a limit to its highest useful

magnification. The general rule is that 60 power is the maximum that can be used for every inch of

aperture, although seeing condition rarely allow this.

diameter. Multiplying 10 by 60 gives a maximum useful magnification of 600 power. Although this is the

maximum useful magnification, most observing is done in the range of 20 to 35 power for every inch of

aperture, which is 200 to 350 for the Star Hopper

Determining Field of View

Determining the field of view is important if you want to get an idea of the angular size of the object that

you are observing. To calculate the actual field of view, divide the apparent field of the eyepiece (supplied

by the eyepiece manufacturer) by the magnification. In equation format, the formula looks like this:

True Field =

As you can see, before determining the field of view, you must calculate the magnification. Using the

example above, we can determine the field of view using the same 25mm eyepiece. The 25mm eyepiece

has an apparent field of view of 52°. Divide the 52° by the magnification, which is 48 power for the Star

Hopper

8. This yields an actual field of 1.08°, or a little over a degree. The apparent field of each

eyepiece that Celestron manufactures is found in the Celestron Accessory Catalog (#93685).