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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] gmx de>
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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Ken <tyl### [at] pacbellnet> 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...
If it's not a mathematically perfect paraboloid you might get some
bumps or other unwanted distortions.
--
#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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Warp wrote:
> POV-Ray can make perfectly parabolic mirrors and reflect light from
> them. It's far from impossible.
Well, I think it's *nearly* impossible to simulate optical instruments
like telescopes with POV-Ray. Of course you could place the camera at
the focal-point of the lens or mirror and get the magnification effect,
but you can't simulate other effects.
For example, I once tried to simulate how saturn would look if being
viewed through a telescope with different mirror-diameters (the larger
the mirror, the sharper the picture) - but it didn't work. If anybody
has ever managed to simulate such things with POV-Ray I'd be interested...
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From: Sir Charles W Shults III
Subject: Re: Help Creating parabolic mirrors
Date: 11 Aug 2003 05:49:57
Message: <3f3766c5$1@news.povray.org>
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Some things can be simulated, but I think (based on what I have found with
my experiments) that the resolution of the image being "magnified" is the
problem- it breaks into big fuzzy blocks.
Cheers!
Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip
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Thanks to all for the clarification.
Any human eye objects-models out there?
Michael
"Warp" <war### [at] tagpovrayorg> wrote in message
news:3f36d670@news.povray.org...
> Ken <tyl### [at] pacbellnet> 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...
>
> If it's not a mathematically perfect paraboloid you might get some
> bumps or other unwanted distortions.
>
> --
> #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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On Mon, 11 Aug 2003 09:46:43 -0400, "Michael" <mji### [at] netscapenet> wrote:
>Thanks to all for the clarification.
>Any human eye objects-models out there?
>Michael
>
The site is down as I write but try
http://www.3dcafe.com/asp/freestuff.asp
Regards
Stephen
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In article <3f3747b3$1@news.povray.org>,
sascha <sas### [at] userssourceforgenet> wrote:
> > POV-Ray can make perfectly parabolic mirrors and reflect light from
> > them. It's far from impossible.
>
> Well, I think it's *nearly* impossible to simulate optical instruments
> like telescopes with POV-Ray. Of course you could place the camera at
> the focal-point of the lens or mirror and get the magnification effect,
> but you can't simulate other effects.
Telescopes could be done even without photons. A reflecting telescope
could be done in any version of POV that supported reflection, a
refracting one in any version supporting refraction.
> Of course you could place the camera at the focal-point of the lens
> or mirror and get the magnification effect,
You can put the camera at the eyepiece, as you would do with a
real-world camera and telescope.
> but you can't simulate other effects.
You mean wave effects like diffraction? It is true you can't simulate
it, though you could fake it if you really wanted. POV is not designed
for optics simulations, but it is a lot more powerful than you seem to
think.
> For example, I once tried to simulate how saturn would look if being
> viewed through a telescope with different mirror-diameters (the larger
> the mirror, the sharper the picture) - but it didn't work. If anybody
> has ever managed to simulate such things with POV-Ray I'd be interested...
Well, with astronomical telescopes, you will just run into precision
problems. This has nothing to do with how well POV simulates optics.
--
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:
>
> Well, with astronomical telescopes, you will just run into precision
> problems. This has nothing to do with how well POV simulates optics.
>
I was refering to another effect which makes objects appear blurry in a
telescope. I'm not sure what causes this effect, but I think it is
bacause the mirror (a paraboloid) will focus only parallel rays (the
object to be viewed must be either a point or ininitely far away). A
planet is neither of both, so not all the light from the planet will be
focused an the same plane, resulting in a blurry image. It gets better
if you use a larger mirror (I guess that's the reason why they use 8
meter mirrors in the VLT :-)
I'm not an astronomer, so I'm not sure about all this!
Maybe this effect can be simulated with POVs focal blur somehow, but I
didn't get it to work.
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Among other things, sascha wrote:
> I was refering to another effect which makes objects appear blurry in a
> telescope. I'm not sure what causes this effect, but I think it is
> bacause the mirror (a paraboloid) will focus only parallel rays (the
> object to be viewed must be either a point or ininitely far away). A
> planet is neither of both, so not all the light from the planet will be
> focused an the same plane, resulting in a blurry image. It gets better
> if you use a larger mirror (I guess that's the reason why they use 8
> meter mirrors in the VLT :-)
The main reason for using large telescopes (with large mirrors) is they
receive more light and so allow astronomers to study fainter and more
distant objects.
--
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby
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Wasn't it Jellby who wrote:
>Among other things, sascha wrote:
>
>> I was refering to another effect which makes objects appear blurry in a
>> telescope. I'm not sure what causes this effect, but I think it is
>> bacause the mirror (a paraboloid) will focus only parallel rays (the
>> object to be viewed must be either a point or ininitely far away). A
>> planet is neither of both, so not all the light from the planet will be
>> focused an the same plane, resulting in a blurry image. It gets better
>> if you use a larger mirror (I guess that's the reason why they use 8
>> meter mirrors in the VLT :-)
>
>The main reason for using large telescopes (with large mirrors) is they
>receive more light and so allow astronomers to study fainter and more
>distant objects.
But there is also the effect of diffraction limited resolution.
Diffraction can cause two closely spaced light sources to appear to be a
single source. It's purely a wave effect, so a ray tracer (even one that
fires photons) won't naturally simulate the effect.
By the time the light from Saturn gets here, the wave fronts are
effectively planar. The wave fronts associated with two different points
on the surface of Saturn are at a slight angle to each other. To a first
approximation (further approximations get quite complicated[1]) for a
perfect mirror, if the angle is insufficient to cause the waves to be in
phase at one edge of the mirror and half a wavelength out of phase at
the opposite edge, then the two points cannot be resolved.
With a wider aperture, the angle between the waves that gives a half-
wavelength difference is smaller and so closer objects can be resolved.
[1]<http://www.pha.jhu.edu/~jlotz/aoptics/node2.html>
--
Mike Williams
Gentleman of Leisure
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Okay, make me a spotlight using a parabolic mirror, while reflecting light,
and as clearly indicated from my context, not use photons...
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Greg M. Johnson <gregj;-)565### [at] aolcom> wrote:
> not use photons...
Why not?
You said that a raytracer couldn't do it. Of course it can do it.
Photon mapping is raytracing by all definitions of the word.
--
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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