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More Terms
•Magnitude: This is a term to describe the brightness of a star or object in the night sky.
The smaller the number the brighter the object is. Some guy in the far flung distant past
coined the term and the differences from one number to the next. The system has
undergone some changes but it is still in use. It is something interesting to look up if one
wants to know some background on some of the founding principles of Astronomy.
•Focal Length: Generally expressed, focal length is the distance (given in millimeters)
between the telescope's primary lens or mirror and the point where the light rays come
together in focus. Why is this important? Focal length is the major determining factor of
any given telescope's magnifying power.
•Objective Lens Size: In a telescope the objective is the lens at the front end of a
refractor or the image-forming primary mirror of a reflecting or catadioptric telescope. A
telescope's light-gathering power and angular resolution are both directly related to the
diameter (or "aperture") of its objective lens or mirror.
•Telescope F-Stop: The f-stop, f-number, is the lens speed of the telescope. It is the result
of dividing the focal length of the lens with the aperture of the eyepiece. The wider the
aperture, the more light it lets through, and the lower the f-stop number. A telescope
with a short f ratio (usually f4 or f5) is considered a rich field telescope and is suited for
viewing the skies in wide views such as constellations, nebulae, clusters and other rich,
scattered items. A telescope with a medium f ratio (usually f6 to f8) is considered a good
all purpose telescope f ratio.
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