40-04135 8 Page Manual Template 6/29/05 10:54 AM Page 14
What do the specifications mean? Optical tube focal length is simply a
12measurement 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 60mm or 2.4 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/11.7. 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 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 700mm. 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: 700 ÷ 13, which equals 53.8. Round this off to the nearest whole number and your new eyepiece magnifies objects 54 times.
If you use your 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.
