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tube. In other words, this is the distance
light travels in the telescope before being
brought to focus in you eyepiece. Your tube is
900mm long.
Primary diameter is how big the mirror is on
your scope. Telescopes are always described
by how large their primary mirror is. Your
telescope is 114mm or 4.5 inches. Other
telescopes are 90mm, 8 inches, 16 inches, or
even 3 feet in diameter. The Hubble
Telescope’s objective mirror has a diameter
of 2.4 meters (that’s 7.8 feet across!).
The focal ratio helps determine how fast the
photographic speed of a telescope is. The
lower the focal ratio number, the faster the
exposure. f/5 is faster than f/10. The faster
the ratio, the faster exposure time is needed
when a camera is hooked up to the
telescope. Your telescope has slower focal
ratio at f/8. Sometimes, astronomers use
focal reducers to make slow exposure
telescopes have faster focal ratios.
USE THE SPECIFICATIONS TO CALCULATE
THE MAGNIFICATION OF YOUR EYEPIECE
The power of a telescope is how much it
magnifies objects. Your 25mm eyepiece
magnifies an object 28 times. Your 9mm
eyepiece magnifies objects 78 times.But if
you obtain other eyepieces, you can calculate
how much magnification they have with your
telescope. Just divide the focal length of the
telescope by the focal length of the eyepiece.
Focal Length of the Telescope
÷
Focal Length of the Eyepiece
=
Magnification
Look at the specifications. You will see that
the focal length of your scope is 900mm.
Let’s say that you have obtained a
13mm eyepiece. You can tell that what
the focal length of your eyepiece is as it
is always printed on the side of an
eyepiece. Divide: 900 ÷ 13, which equals
69.2. Round this off to the nearest whole
number and your new eyepiece magnifies
objects 69 times.
If you use a Barlow lens with one of your
eyepieces, it doubles the magnification of
your eyepiece. Other types of Barlows can
triple or further increase the power of an
eyepiece. To find out how much your
magnification is when you use a Barlow,
multiply your eyepiece’s magnification
by two.
Your 25mm low-power eyepiece magnifies
an object 28 times. Multiply 28 by 2 and you
get 56 times magnification with a Barlow.
Eyepiece’s magnification x 2
=
Magnification with a 2X Barlow lens
It’s worth repeating: Keep in mind that a
bright, clear, but smaller image is more
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ASTRONOMY RESOURCES
• The Meade 4M Community
6001 Oak Canyon, Irvine, CA 92618
• Astronomical League
Executive Secretary
5675 Real del Norte, Las Cruces, NM 88012
• The Astronomical Society of the Pacific
390 Ashton Ave., San Francisco, CA 94112
• The Planetary Society
65 North Catalina Ave, Pasadena, CA 91106
• International Dark-Sky Association, Inc.
3225 N. First Avenue, Tucson, AZ 85719-2103
Looking at or near the Sunwill cause irreversabledamage to your eye. Do not point this telescope at or near the Sun. Do not look through the telescope as it is moving.
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