To compare light-gathering ability of a compound scope versus a refractor, shouldn't the area of the secondary mirror be subtracted? Don't compound scopes really only have the light gathering ability of a 10-15% smaller refractor?
Light gathering - compound vs refractor
Started by hemismith, 05/22/2006 09:39PM
Posted 05/22/2006 09:39PM
Opening Post
Posted 05/22/2006 10:01PM
#1
Craig Smith said:
To compare light-gathering ability of a compound scope versus a refractor, shouldn't the area of the secondary mirror be subtracted? Don't compound scopes really only have the light gathering ability of a 10-15% smaller refractor?
Technically, yes, a 10" SCT should be about equivalent to a 9" refractor. But since differences of brightness this subtle are difficult for the human eye to detect, the factor is usually ignored.
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