# rec.photo.misc

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

In rec.photo.equipment.35mm Michael Weinstein wrote:
: On 2006-04-26 00:37:03 -0400, Frank Pittel said:

: > In rec.photo.equipment.35mm Michael Weinstein
: > wrote:
: > : On 2006-04-24 17:27:28 -0400, "alex" said:
: >
: > : > : > "Dave Hillstrom" wrote in message :
: > > news:1145843218.216398.119160@i39g2000cwa.googlegroups.com...
: > : >> 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.
: > : >> : > : > Someone wasn't concentrating in Physics at school...
: >
: > : No, I think someone didn't actually TAKE Physics in school.
: >
: > When I was taking physics light traveled slower in water then in air.

: And it still does. But that doesn't confer any sense to the OP's
: statement. Lenses are not built according to the speed of light.

I've never used a camera under water. My cameras aren't water proof and I
doubt the water will do the inside of my cameras any good.

As memory servers when light goes from an object of a given density to an
object of another density the light is "bent". The amount is determined by
the wavelength of the light. That's why passing light through a prism or even
water will create a "rainbow".

The elements of modern lenses have coatings on the to minimize the bending of light
between elements. It makes sense that the formulation of the coating would be to compensate
for the differences in densities of the lens elements and air. In that case the
difference in density between air and water would make the coating less then
optimum.
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