If anyone has the time I could sure use some help creating three objects

First an annular parabolic mirror.
-Made of solid glass or hollow
-Having an adjustable parabolic curve in order to change the focal length
It would look like a clear or hollow  parabolic torus cut in half with 
its interior surface mirrored, interior media clear or hollow and its 
exterior opaque.

Second a parabolic mirror
-Made of glass and hollow
-Having an adjustable parabolic curve in order to change the focal length
It would look like a parabolic bowl with its interior surface mirrored, 
interior media clear or hollow, and its exterior surface opaque

Third an omni-directional mirror
-Made of glass and hollow
-Having an semitransparent external mirror coating while the interior 
would be fully transparent
It would look like a cone with a rounded apex with its exterior surface 
  coated with a semitransparent mirrored interior surface fully transparent

Thanks

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You can create paraboloids using the quadric object.
Here's a mirror as it is used in a Newton reflector-telescope:

#default {
	pigment { color rgb <1,1,1> }
	finish { ambient 0.5 diffuse 0.5 }
}

#declare focal_length = 10;
#declare ms = 1/4/focal_length;
#declare mainMirror = difference {
	cylinder { <0.01,0,0>,<-ms,0,0>,1 }
	quadric {
		<0,1,1>,<0,0,0>,<1,0,0>,0
		scale <ms,1,1>
		finish { ambient 0 diffuse 0 reflection 1 }
	}
}


plane { y,-2 pigment { checker } }
light_source { <-100,100,0> color rgb <1,1,1> }
camera { location <-3,1,-3> look_at <0,0,0> }

object { mainMirror }

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sascha wrote:

> You can create paraboloids using the quadric object.
> Here's a mirror as it is used in a Newton reflector-telescope:
> 
Wouldn't it be easier to use a lathe with _quadratic_
spline for the parabolic mirror? 

Wolfgang

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In article <3f36803d@news.povray.org>, Wolfgang Wieser <wwi### [at] gmxde> 
wrote:

> Wouldn't it be easier to use a lathe with _quadratic_
> spline for the parabolic mirror? 

The easiest way would be to use an isosurface, a quadric is probably the 
most efficient way. I wouldn't use a lathe, though it would work.

There are paraboloid shapes based on the quadric primitive in 
shapes_old.inc.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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Christopher James Huff wrote:

> In article <3f36803d@news.povray.org>, Wolfgang Wieser <wwi### [at] gmxde>
> wrote:
> 
>> Wouldn't it be easier to use a lathe with _quadratic_
>> spline for the parabolic mirror?
> 
> The easiest way would be to use an isosurface, a quadric is probably the
> most efficient way. I wouldn't use a lathe, though it would work.
> 
A paraboloid is essentially y=x^2 rotated around the Y axis (isn't it??)
So, using a quadratic spline and modelling just that y=x^2 curve 
seems to me the most natural approach to me. 

Why should I use a quadric? Is it really faster than a lathe?

Wolfgang

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I hope this isn't a patronizing question, but I fear you may be expecting a
raytracer to do something it cannot.  I once spent a weekend trying to use
CorelDream3D to make my own "spotlight":  a parabolic mirror with a light
source in it.  It don't work.

You'll need to use photons if you want to make "optical" use of such a
surface.

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Wolfgang Wieser <wwi### [at] gmxde> wrote:
> Why should I use a quadric? Is it really faster than a lathe?

  A quadric will be mathematically accurate (inside the limits of
floating point accuracy), while a lathe will only be an approximation.
  As for speed, the quadric is probably faster.

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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Greg M. Johnson <gregj;-)565### [at] aolcom> wrote:
> I hope this isn't a patronizing question, but I fear you may be expecting a
> raytracer to do something it cannot.

  POV-Ray can make perfectly parabolic mirrors and reflect light from
them. It's far from impossible.

-- 
plane{-x+y,-1pigment{bozo color_map{[0rgb x][1rgb x+y]}turbulence 1}}
sphere{0,2pigment{rgbt 1}interior{media{emission 1density{spherical
density_map{[0rgb 0][.5rgb<1,.5>][1rgb 1]}turbulence.9}}}scale
<1,1,3>hollow}text{ttf"timrom""Warp".1,0translate<-1,-.1,2>}//  - Warp -

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In article <3f3696fe@news.povray.org>, Wolfgang Wieser <wwi### [at] gmxde> 
wrote:

> A paraboloid is essentially y=x^2 rotated around the Y axis (isn't it??)
> So, using a quadratic spline and modelling just that y=x^2 curve 
> seems to me the most natural approach to me. 

A more precise description would be "y = x^2 + z^2", though it is 
equivalent to sweeping a 2D curve as you described.


> Why should I use a quadric? Is it really faster than a lathe?

A quadric would be a paraboloid, while a lathe would just look like one. 
As for speed, a lathe is a far more complex object. I would expect 
slower rendering and much higher probability of artifacts. Also, 
although there is a quadratic spline, it may not give the expected 
result, and would be a bit more awkward to control...splines are 
generally not used for precise mathematical curves. A lathe *can* be 
used for this, but it is certainly not the best tool for the job. An 
isosurface or quadric would be a perfect match for this task. A quadric 
is more difficult to use than an isosurface, but the isosurface will be 
less precise. Either one may be faster, it depends on the situation.

And finally, there are already predefined paraboloid quadrics in the 
includes...

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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Christopher James Huff wrote:

> A quadric would be a paraboloid, while a lathe would just look like one.

If it looks like a duck and it quacks like a duck...

-- 
Ken Tyler

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