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Reversed from left to right, as
viewed with a Star Diagonal
Inverted image, as viewed with
the eyepiece directly in telescope
A telescope is an instrument that collects and focuses light. The nature of the optical design determines how the light is focused.
Some telescopes, known as refractors, use lenses. Other telescopes, known as reflectors, use mirrors. The NexStar 60, 80 and
102 telescopes are refractor telescopes that use an objective lens to collect its light. The NexStar 114 and 130 are reflecting
telescopes with a primary and secondary mirror to gather and focus light.
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Once you have found an object in the telescope, turn the focusing knob until the image is sharp. To focus on an object that is
nearer than your current target, turn the focusing knob toward the eyepiece (i.e., so that the focusing tube moves away from the
front of the telescope). For more distant objects, turn the focusing knob in the opposite direction. To achieve a truly sharp focus,
never look through glass windows or across objects that produce heat waves, such as asphalt parking lots.
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The image orientation of any telescope changes depending on how the eyepiece is inserted into the telescope. When observing
through the NexStar 60, 80 or 102 using the diagonal, the image will be right side up, but reversed from left to right. When
observing straight through, with the eyepiece inserted directly into the telescope, the image will be inverted.
When observing through the NexStar 114 or 130, a reflecting telescope, the image will reversed (mirror image) when looking
through the eyepiece.
For astronomical viewing, out of focus star images are very diffuse, making them difficult to see. If you turn the focus knob too
quickly, you can go right through focus without seeing the image. To avoid this problem, your first astronomical target should
be a bright object (like the Moon or a planet) so that the image is visible even when out of focus.
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You can change the power of your telescope just by changing the eyepiece (ocular). To determine the magnification of your
telescope, simply divide the focal length of the telescope by the focal length of the eyepiece used. In equation format, the
formula looks like this:
Focal Length of Telescope (mm)
Magnification = ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯
Focal Length of Eyepiece (mm)
Let’s say, for example, you are using the 25mm eyepiece. To determine the magnification you simply divide the focal length of
your telescope (for example, the NexStar 114 has a focal length of 1000mm) by the focal length of the eyepiece, 25mm.
Dividing 1000 by 25 yields a magnification of 40 power.