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LCM 60/80 - Inverted image
when viewing with the eyepiece
straight through (no diagonal)
LCM 114 – Upside down 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 LCM
60 and 80 telescopes are refractor telescopes that use an objective lens to collect its light. The LCM 114 is a 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 LCM 60 or 80 using the diagonal, the image will be right side up. When observing straight through,
with the eyepiece inserted directly into the telescope, the image will be inverted.
When observing through the LCM 114, a reflecting telescope, the image will be rotated 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 LCM 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.
Although the power is variable, each instrument under average skies has a limit to the highest useful magnification. The
general rule is that 60 power can be used for every inch of aperture. For example, the LCM 114 is 4.5” (114mm) in
diameter. Multiplying 4.5 by 60 gives a maximum useful magnification of 270 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 90 to 158
times for the LCM 114 telescope.
