# rec.photo.misc

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

In article <4e6dnSOiiv3d1svZRVn-ug@giganews.com>, Frank Pittel
writes
>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".

Wavelength dispersion only occurs under some circumstances, and can be
positive or negative, hence you can introduce a two identical
refractions in a ray using flint and crown glass with no dispersion.
You can have material which does not introduce dispersion but does
refract.

>The elements of modern lenses have coatings on the to minimize the
>bending of light
>between elements.

The function of the coating is to reduce reflection from the surface, if
you prevented refraction the lens would not focus light and you might as
well use a piece of plain glass.

>It makes sense that the formulation of the coating would be to
>compensate
>for the differences in densities of the lens elements and air.

This makes no sense.

>In that case the
>difference in density between air and water would make the coating less then
>optimum.

Nonsense, It is the thickness (more accurately the path duration) that
is important.
--
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 =>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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