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Subject: Re: You use different lenses underwater because the speed of light is different



In article <1145864866.698218.269710@e56g2000cwe.googlegroups.com>,
cjcampbell writes
>
>Prometheus wrote:
>> In article <1145858451.759527.73370@u72g2000cwu.googlegroups.com>,
>> cjcampbell writes
>> >
>> >Dave Hillstrom wrote:
>> >> You can't use regular lenses underwater, that's why you always see
>> >> special cameras on ocean documentaries and such. People think it's
>> >> because they need to be waterproof but the real reason is the speed of
>> >> light underwater is different than in air and it makes the light bend
>> >> at different angles through the lenses.
>> >> Einstein proved it.
>> >
>> >So, I suppose that is also the reason you need different lenses to take
>> >telephoto pictures than the lenses you would use for wide angle. Light
>> >from different distances travels at different speeds? No doubt this is
>> >due to the fact that light traveling from farther away has to go
>> >through more haze, so it passes through more water on the way to the
>> >camera. It would explain depth of field, too. A lens set at a
>> >particular focal length can only bend light traveling at a particular
>> >speed at the correct angle. Light that is going too fast or too slow
>> >would, of course, bend at the wrong angle and thus the foreground and
>> >background are out of focus. That being the case, you would also need
>> >special lenses in space, where light does not travel through any water
>> >at all.
>> >
>> >Or maybe it is just wrong to encourage this nut.
>>
>> No, it is you who is wrong. Light DOES travel at a lower speed through
>> water than air The refraction at the water/glass interface of the front
>> element when immersed in water is very different to the air/glass
>> interface when in air. The effect of water vapour in air is much, much
>> less; although droplets will cause random refractions and make objects
>> blurred.
>
>Okay, seriously, I know that the speed of light changes slightly as it
>travels through water, glass, and just about anything else. That said,
>the lenses used in underwater photography work perfectly well on dry
>ground, in space, or just about anywhere else.
>
>I should have known that attempting any humor at all on Usenet is
>dangerous...

Using a lens designed for one refractive index medium in another could
severely compromise your focal range, it might also negate some of the
aberration correction; I suppose it depends on your definition of
"perfectly well".
--
Ian G8ILZ

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You use different lenses underwater because the speed of light is different =>Re: You use different lenses underwater because the speed of light is different =>Re: You use different lenses underwater because the speed of light is different =>Re: You use different lenses underwater because the speed of light is different =>

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