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How to stop down a Canon EOS lens
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08-07-2010, 08:38 PM
troypiggo
(Troy)
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Join Date: Nov 2008
Location: Brisbane, Australia
Posts: 4,846
Not 50mm, that's half the diameter but you're after half the area for one full stop like f/2.8 to f/4. It'd be 100 divided by root 2 (1.4 approx). That's about 70mm. That's if my maths is right this time of night after 2 beers with dinner.
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