Meade114EQAR 3/28/07 9:52 AM Page 17
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
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
3225 N. First Avenue, Tucson, AZ
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 15 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
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
Looking at or near the Sun will cause irreversable damage to your eye. Do not point this telescope at or near the Sun. Do not look through the telescope as it is moving.
