POV-Ray : Newsgroups : povray.general : One way glass / sunglasses Server Time
2 Aug 2024 04:19:26 EDT (-0400)
  One way glass / sunglasses (Message 1 to 3 of 3)  
From: Rick Measham
Subject: One way glass / sunglasses
Date: 13 Feb 2005 01:28:45
Message: <420ef39d$1@news.povray.org>
I've now created my sunglasses by hand (I'll post into PBI in a couple 
of minutes). However I'm not happy with the lenses. I don't want a 
surface that's 100% opaque, like using a silver or chrome. But right now 
I'm having the problem that my specs are semi transparent and so the 
surface behind them is being reflected around and is visible through the 
glasses. (If that's not the phenomena I'm seeing, please correct me)

Has anyone done such a surface before? I'd love it to REALLY be one-way 
so that I can see from the back, but no the front.

Cheers!
Rick Measham


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From: Tim Cook
Subject: Re: One way glass / sunglasses
Date: 13 Feb 2005 02:02:59
Message: <420efba3@news.povray.org>
Rick Measham wrote:
> Has anyone done such a surface before? I'd love it to REALLY be one-way 
> so that I can see from the back, but no the front.

You're looking for a way to make a one-way mirror.  From wikipedia:
"A one-way mirror, also called two-way mirror (!), reflects about half 
of the light and lets the other half pass. It is a sheet of glass coated 
with a layer of metal only a few dozen atoms thick, allowing some of the 
light through the surface (from both sides). It is used between a dark 
room and a brightly lit room. Persons on the brightly lit side see their 
own reflection -- it looks like a normal mirror. Persons on the dark 
side see through it -- it looks like a transparent window. It may be 
used to observe criminal suspects or customers (to watch out for theft). 
The same type of mirror, when used in an optical instrument, is called a 
half-silvered mirror. Its purpose is to split a beam of light so that 
half passes straight through, while the other half is reflected -- this 
is useful for interferometry."

As far as how to do this in POV...since thickness of an object is 
irrelevant to material properties, and precludes simulating several 
material properties...perhaps experiment with semitransparent reflective 
materials, but you can assign different materials to the 'inside' and 
'outside' of an object.  'interior_texture' is the keyword iirc.

-- 
Tim Cook
http://home.bellsouth.net/p/PWP-empyrean

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From: J  F  Miller
Subject: Re: One way glass / sunglasses
Date: 27 Feb 2005 01:50:00
Message: <web.42216c81ef7853fa60ec80cf0@news.povray.org>
Rick Measham <nomail@nomail> wrote:
> I've now created my sunglasses by hand (I'll post into PBI in a couple
> of minutes). However I'm not happy with the lenses. I don't want a
> surface that's 100% opaque, like using a silver or chrome. But right now
> I'm having the problem that my specs are semi transparent and so the
> surface behind them is being reflected around and is visible through the
> glasses. (If that's not the phenomena I'm seeing, please correct me)
>
> Has anyone done such a surface before? I'd love it to REALLY be one-way
> so that I can see from the back, but no the front.
>
> Cheers!
> Rick Measham

I think I can guess the problem.  You have applied a semi transparent
reflective texture to the whole lens.  For sunglasses, only the front face
of the lens is mirrored.  to correct the problem apply your gurrent texture
to one half the part of a CSG element forming just the front half the lens
and a different on to the back.

JFMILLER


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