SOLUTION: What is the f number of a 15cm diameter, .9 focal length lens?

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Question 173661: What is the f number of a 15cm diameter, .9 focal length lens?
Answer by Mathtut(3670) About Me  (Show Source):
You can put this solution on YOUR website!
f stop or focal ration would be equal to focal length divided by the diameter of the lens
:f=fstop
F=focal length
D=diameter of lens
f=F/D
:
highlight%28f=.9%2F15=.06%29 usually diameters of lens are in mm so this is a very large aperature
this of course was assuming the the focal length was in centimeters also