Meade Instruments RB-70 User Manual
Page 13
Surf the Web and visit your local library:
The internet contains a huge amount of
astronomical information, both for children
and adults. Check out astronomy books from
your library. Look for star charts—these are
available on a monthly basis in
Astronomy
and
Sky and Telescope
magazines.
HAVE A GOOD TIME,
ASTRONOMY IS FUN!
SPECIFICATIONS
Optical tube focal length . . . . . . . . . 700mm
Objective lens diameter . . . . . 70mm (2.75")
Focal ratio . . . . . . . . . . . . . . . . . . . . . . . . f/10
Mounting type . . . . . . . . . . . . . . . Altazimuth
What do the specifications mean?
Optical tube focal length is simply a
measurement of the length of the optical
tube. In other words, this is the distance
light travels in the tele-scope before being
brought to focus in you eyepiece. Your tube is
700mm long.
Objective lens diameter is how big the
lens is on your scope. Telescopes are
always described by how large their
objective lens is. Your telescope is 70mm or
2.75 inches. Other telescopes are 90mm, 8
inches, 16 inches, or even 3 feet in
diameter. The Hubble Telescope’s objective
lens 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 tele-
scope. Your telescope has slower focal ratio
at f/10. Sometimes, astronomers use focal
reducers to make slow exposure telescopes
have faster focal ratios.
Altaz mounting simply means your telescope
moves up and down (altitude or “alt”), and
side to side, (azimuth or “az”). Other
mounting configurations are available for
other telescopes, such as equatorial
mounting.
USE THE SPECIFICATIONS TO CALCULATE
THE MAGNIFICATION OF YOUR EYEPIECE
The power of a telescope is how much
it magnifies objects. Your 25mm eyepiece
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 Avenue, San Francisco, CA 94112
•
The Planetary Society
65 North Catalina Avenue, Pasadena, CA 91106
•
International Dark-Sky Association, Inc.
3225 N. First Avenue, Tucson, AZ 85719-2103
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
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