
Get Your
Moon Observer's Software Toolkit!
Telescopes on Amazon
Celestron 127EQ PowerSeeker Telescope
Illustrated Guide to Astronomical Wonders: From Novice to Master Observer
Hubble: Imaging Space and Time
|
Telescope Optics
The capacity of a telescope to focus light is dependant on many features
such as the aperture, magnification, focal length and ratio, not to mention wave error and
resolution. These are the important features to bear in mind when purchasing a
telescope. Purchasing quality telescope is important as it vastly improves the quality of the
images and pictures you will produce.
Basically, an aperture is a hole or an opening through which light is admitted. But more importantly
an aperture determines the quality of the light waves admitted into the telescope. The narrower the aperture
the sharper, but darker the resultant image maybe.
Thus the aperture relates to the telescopes ability to focus light. The focusing also depends on the
size of the lens or mirror. The bigger the lens used, the brighter the image.
Aperture is hugely important, but bigger isn’t always best, so take other
features into consideration, too.
Magnification depends on a variety of things namely the lenses and distance to
the eyepiece. As a
guide, 40-60x per inch of aperture is sufficient. Low
magnifications give the best light in most cases.
Focal length. The longer the focal length - the distance the light travels from the
lens to eyepiece, the higher the magnification. Focal length is not the same as
the length of the telescope. Rather, it is the optical length of the telescope's lens.
Compound telescopes actually fold the path of the light making the optical length
longer than the length
of the tube. Eyepieces have focal lengths, also (typically between 4-50mm). To calculate a telescope's
magnification power,
you divide the focal length of the telescope by the focal length of the eyepiece.
Focal ratio tells you the relative brightness and field of view. The focal ratio is defined as
the relationship between the focal length and the aperture. A 10-inch scope with the focal length of
100 inches would have the focal ratio of 10. This would be expressed as f/10 or f10.
Similar to cameras, the lower the focal ratio the faster (brighter) the optical system. Lower focal
ratios have gentler curve to their optical elements and produce less optical aberrations.
F/10 and above
is for viewing the moon, planets and stars. F/8 meets most general purpose
requirements and F/6 and below is for viewing far distant objects.
The wave error gives you a measurement of the the quality of the mirror or lens in the
telescope. A wave error occurs when the light's wavelength is shifted or othe distortions occur.
The wave error is epxressedas a fraction and the smaller the number, the more perfect the quality.
The overall rating number for a telescope
represents the accumulated wave error numbers of each lens or mirror; an absolute minimum is
one-fourth. A wave error of 1/4 is typical of many mass-produced telescopes.
Resolution. The better resolution that a telescope has the better the clarity of the details
of the images. Resolution also reflects the telescopes ability to separate
two close objects - say two moons of Jukopitor whose orbits are crossing.
About the Author: Scott Harker is the publisher of several websites including:
Sherlock Holmes Pastiches,
Harvest The Sun | Wind Power,
Signs of Pregnancy,
Meditation - The Inner Journey, and
Health News.
Buy Land on the Moon from The Lunar Registry makes a great gift!
Includes personalized deed, actual satellite property photo and
a detailed information sheet.
Please click here to learn more!
| |
News About Telescopes and Optics
Google News
|