Thread: F-ratio myth
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Old 21-02-2018, 08:41 PM
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Camelopardalis (Dunk)
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Camelopardalis is offline
Join Date: Feb 2013
Location: Brisbane
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The light beam might be parallel as it enters the scope but as soon as it hits a lens or a mirror it is bent into a cone of light.

The steepness of the cone of light is directly related to its focal ratio.
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