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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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.

-- 
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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.

-- 
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