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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 Maksutov-Cassegrain
optical system uses a combination of mirrors and lenses and is referred to as a compound or catadioptric telescope. This unique
design offers large-diameter optics while maintaining very short tube lengths, making them extremely portable. The Maksutov-
Cassegrain system consists of a corrector plate, a spherical primary mirror, and a secondary mirror spot. Once light rays enter the
optical system, they travel the length of the optical tube three times.
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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.
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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The image orientation of any telescope changes depending on how the eyepiece is inserted into the telescope. When
observing through the 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.
Reversed from left to right, as
viewed with a Star Diagonal
Inverted image, as viewed with
the eyepiece directly in telescope
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