Comparison shopping for Telescopes?
Department stores and so-called Discount stores often sell telescopes
designed to appeal to novice observers with limited observing experience.
Advertisements for these telescopes promote purchases with slogans and jargon.
These advertisements emphasize low price and high power and ignore more
important technical information such as eyepiece size, effective power, mount
type, mount stability, optical quality, and focal length.
The Magnifying Power Fallacy promoted in typical advertisements is:
"Buy Brand X telescope because it can magnify 700 times!"
The Magnifying Power Fact is that:
"Small telescopes (less than 4 inches in diameter) can not effectively magnify images more that 250 X."
Claims of higher magnification are misleading because:
- Although reducing eyepiece size increases magnifying power, this increased magnification obscures and dims images. (Magnifying power is computed by dividing focal length of the telescope by focal length of the eyepiece.)
- As a result, telescopes need the light-gathering power provided by large apertures (telescope diameters) to retain brightness and sharpness at higher magnification. Aperture diameter controls and limits effective power to 50-60x per inch; so, small 60 mm.(2.4 in.) aperture telescopes have maximum effective power of 120-144X.
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A Hubble Space Telescope survey found enough galaxies to conclude that there are 2 to 3 million visible per square degree of sky. This means that there are at least 80 billion galaxies. Invisible faint/dwarf galaxies probably increase this amount tenfold.
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