10-Inch Truss Tube Scope
Sgr-4
6" Deluxe Reflector Kit
How To Choose:
4 ¼ , 4 ½, Sgr-4
Getting Started in Astronomy: Article for Beginners
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EYEPIECES AND MAGNIFICATION
To people who are experienced with telescopes, magnification is NOT a basis of comparison or ranking between telescopes. Only telescope marketers attempting to make quick sales to the uninformed advertise scopes on the basis of huge magnifications. Light gathering power, resolving power, contrast, and steadiness ARE important. These depend on the aperture (diameter) of the main lens or mirror, and on the quality of the instrument.
Atmospheric conditions frequently limit the magnification that can be used at a given time and place. That is why astronomers have sited major observatories on remote mountain peaks at a handful of almost-inaccessible spots around the Earth. The rest of us usually observe through atmospheric turbulence with much less magnification than theoretically possible. Within limits we can select the magnification of a telescope to suit needs and conditions simply by choosing among eyepieces of different focal lengths, usually ranging from about 32 mm to about 7 mm.
The magnification obtained with a specific eyepiece is simply the focal length of the eyepiece divided into the focal length of the telescope. Forinstance, if the optional 7.5 mm eyepiece is used with the 765 mm focal length Sgr-3 reflector, the magnification would be 765 / 7.5 or 102 times (102 X).
If an eyepiece of too short a focal length is used, the resulting magnification can easily exceed the ability of the atmosphere to transmit clear detailed images. The result is an unclear view made up of "blobs" that wiggle and twist out of shape as atmospheric currents intervene between the telescope ant the object in view. Many nights present "seeing" conditions steady enough to allow use of 30-40 power per inch of aperture. On these nights a 4 1/4-inch sill show remarkable detail at 130 to 150 power.
On exceptional nights up to 50 power per inch of aperture can be used (up to 212 power with a 4 1/4-inch). Obviously, claims of 450 X by suppliers of SMALLER telescopes are misleading and can lead only to frustration!
There are important advantages to using long-focal-length
eyepieces, which give lower magnifications. The field of view of the telescope
becomes much wider and the view crisper. Sky objects are easier to find
and stay in view longer before the rotation of the Earth carries them out
of the viewing field.
| OTHER EYEPIECES FOR THE Sgr-3 3-INCH REFLECTING SCOPE | OTHER EYEPIECES FOR THE 4 1/4-INCH DELUXE KIT |
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