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03-13-2011, 01:58 PM   #16
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The aperture stop number is focal length divided by the diaphragm diameter. If FL increases by a factor 3, so must the opening by the same amount to maintain the same stop number.

03-14-2011, 05:23 AM   #17
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QuoteOriginally posted by RioRico Quote
The camera may *report* that that the aperture is f/4.7 but one *actually* gets f/5.8 there.
Camera 'bots can be tricked; optical physics can't. I know; I just tried it. Can't fool Newton...
Newton didn't contribute that much to optical design, but you're right, you can't fool nature.
03-14-2011, 01:19 PM   #18
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QuoteOriginally posted by bdery Quote
Newton didn't contribute that much to optical design, but you're right, you can't fool nature.
He actually invented the reflecting telescope and had other contributions in optics.
03-15-2011, 04:58 AM   #19
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QuoteOriginally posted by Laurentiu Cristofor Quote
He actually invented the reflecting telescope and had other contributions in optics.
regarding the telescope, you're right, I should have written "lenses design". His other contributions were mainly regarding refraction with plane surfaces. His work on lenses was minimal (but he was a great mind anyway

We physicists don't particularly love him because according to most historical accounts he more or less stole or borrowed many ideas from others and made them his own. But that's just rumours, really :P

03-15-2011, 07:15 AM   #20
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I prefer 50-200wr, it‘s more portable.
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