A common question when purchasing a
what "power" it is. The power of the
the ability to magnify an object.
magnification is really not as important as field of
view of aperture, to determine the power of a
telescope, simply divide the eyepiece diameter to
telescope focal length:
Eyepiece diameter is also known as the eyepiece focal length. Do not confuse this with the exit pupil which is a different concept: based on the telescope aperture and magnification or telescope focal and telescope focal ratio. The exit pupil is the term that defines the size of the light cone that enters your eye.
Additionally, the resolution of a
telescope must be
considered. For ideal "seeing" conditions, the
following formula applies:
Example: a 254mm
telescope (a 10")
The size of an image depends on the focal length of
telescope. For example, the longer the focal
length, the larger the object:
How faint an object can your
Where m is the limiting
magnitude. Example, our 10"
The faintest object a 10"
telescope can see is with
magnitude of 14.7 (Pluto has a
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