raytracing lenses: fake?

raytracing lenses: fake?

Post by William L » Sat, 06 Jun 1998 04:00:00



hello lightwavers,

i am trying to raytrace light (using pointlights or distant lights) on a
surface through a lens.
any refraction seen directly from the camera through the lens is ok.
but i get the feeling that light that passes through the lens and hits
an underlying surface is just the result of filtering the affected
surface with a (color) factor. i mean: no raytracing.

e.g. with real raytracing light through a convex lens would converge.
this is why you can start a fire with a looking glass in the sun. this
is why you get that strange pattern underwater (which needs extreme
amounts of time and power to raytrace of course) and the 'dancing
lights' in the shadow beneath your wineglass on the table .

concave lenses are not a problem since they disperse lightrays. the
raytraced result would usually just look like how lw is doing it right
now.

am i right about the 'half-fake' raytracing (or am i imagining things)?
if i'm right, does anyone have any ideas to simulate the light
convergence through glasses (with/without liquid) or lenses?

thanks.
william li

--

* please remove KILLSPAM from the e-mail address when replying *
* please include 'William Li' in address *
___________________________________________________

van holsteijn en kemna BV
* research * design * engineering *
- Delft - Netherlands
- Brussels - Belgium
___________________________________________________

 
 
 

raytracing lenses: fake?

Post by <.> » Sat, 06 Jun 1998 04:00:00


Raytracing is nearly always a fake as they use a reverse trace, going *from*
the eye to the light, rather than the other way round as in real life.
Because of this, render "caustics" become very rare, as the light hits the
table before the glass and the glass before the liquid etc, projecting light
through refractive material becomes unrealistic, lenses don't work as
expected and prisms don't split light.

Other effects are, no reflecting a light beam in a mirror and no radiosity
effect as secondary reflections lose their luminosity and raytracing uses
straight lines for reflections and don't take into account diffuse materials
which would normally spread any light hitting them.

There are only a couple of renderers which can do this stuff.... none of
them cheap or quick. LW has a "faker" like most others. You can simulate
most of the effects with a little thought using maps, lights and
projector-lights.

--


>hello lightwavers,

>i am trying to raytrace light (using pointlights or distant lights) on a
>surface through a lens.
>any refraction seen directly from the camera through the lens is ok.
>but i get the feeling that light that passes through the lens and hits
>an underlying surface is just the result of filtering the affected
>surface with a (color) factor. i mean: no raytracing.

>e.g. with real raytracing light through a convex lens would converge.
>this is why you can start a fire with a looking glass in the sun. this
>is why you get that strange pattern underwater (which needs extreme
>amounts of time and power to raytrace of course) and the 'dancing
>lights' in the shadow beneath your wineglass on the table .

>concave lenses are not a problem since they disperse lightrays. the
>raytraced result would usually just look like how lw is doing it right
>now.

>am i right about the 'half-fake' raytracing (or am i imagining things)?
>if i'm right, does anyone have any ideas to simulate the light
>convergence through glasses (with/without liquid) or lenses?

>thanks.
>william li

>--

>* please remove KILLSPAM from the e-mail address when replying *
>* please include 'William Li' in address *
>___________________________________________________

>van holsteijn en kemna BV
>* research * design * engineering *
>- Delft - Netherlands
>- Brussels - Belgium
>___________________________________________________


 
 
 

raytracing lenses: fake?

Post by Eric Knight Holbroo » Sun, 07 Jun 1998 04:00:00


Also keep in mind that his glass "lens" is not solid. Big, big factor right
there and on reason Bryce's reflections and refractions, oddly enough from
such a cheap program, can look many times better than Lightwave's.


>Raytracing is nearly always a fake as they use a reverse trace, going
*from*
>the eye to the light, rather than the other way round as in real life.
>Because of this, render "caustics" become very rare, as the light hits the
>table before the glass and the glass before the liquid etc, projecting
light
>through refractive material becomes unrealistic, lenses don't work as
>expected and prisms don't split light.

>Other effects are, no reflecting a light beam in a mirror and no radiosity
>effect as secondary reflections lose their luminosity and raytracing uses
>straight lines for reflections and don't take into account diffuse
materials
>which would normally spread any light hitting them.

>There are only a couple of renderers which can do this stuff.... none of
>them cheap or quick. LW has a "faker" like most others. You can simulate
>most of the effects with a little thought using maps, lights and
>projector-lights.

>--


>>hello lightwavers,

>>i am trying to raytrace light (using pointlights or distant lights) on a
>>surface through a lens.
>>any refraction seen directly from the camera through the lens is ok.
>>but i get the feeling that light that passes through the lens and hits
>>an underlying surface is just the result of filtering the affected
>>surface with a (color) factor. i mean: no raytracing.

>>e.g. with real raytracing light through a convex lens would converge.
>>this is why you can start a fire with a looking glass in the sun. this
>>is why you get that strange pattern underwater (which needs extreme
>>amounts of time and power to raytrace of course) and the 'dancing
>>lights' in the shadow beneath your wineglass on the table .

>>concave lenses are not a problem since they disperse lightrays. the
>>raytraced result would usually just look like how lw is doing it right
>>now.

>>am i right about the 'half-fake' raytracing (or am i imagining things)?
>>if i'm right, does anyone have any ideas to simulate the light
>>convergence through glasses (with/without liquid) or lenses?

>>thanks.
>>william li

>>--

>>* please remove KILLSPAM from the e-mail address when replying *
>>* please include 'William Li' in address *
>>___________________________________________________

>>van holsteijn en kemna BV
>>* research * design * engineering *
>>- Delft - Netherlands
>>- Brussels - Belgium
>>___________________________________________________

 
 
 

raytracing lenses: fake?

Post by Jeremy Bir » Sun, 07 Jun 1998 04:00:00



> Other effects are, no reflecting a light beam in a mirror and no radiosity
> effect as secondary reflections lose their luminosity and raytracing uses
> straight lines for reflections and don't take into account diffuse materials
> which would normally spread any light hitting them.

> There are only a couple of renderers which can do this stuff.... none of
> them cheap or quick.

None of them are cheap AND quick, but if you have enough time to learn the
program, Blue Moon Rendering Tools is very cheap (I think it's still only $20) see
http://www.seas.gwu.edu/student/gritz/bmrt.html

--
Jeremy Birn
3dRender.com: http://www.3dRender.com/
--

 
 
 

raytracing lenses: fake?

Post by Atomic Sku » Sun, 07 Jun 1998 04:00:00



Quote:

>Also keep in mind that his glass "lens" is not solid. Big, big factor right
>there and on reason Bryce's reflections and refractions, oddly enough from
>such a cheap program, can look many times better than Lightwave's.

  You'll often find examples of cheaper programs having a few features found
only in high end apps..

  Imagine's bones for example walk all over Lightwave's..  point groups,
falloff between point groups, etc..  But I still wouldn't want to use it for
anything serious.

  Kinda destroys the "Lightwave is a midrage package so SHUT UP about it's bone
limitations!" response I saw a while back though..

--
                             -=Atomic Skull=-

     See my 3-D anime character page, www.ns.net/~Argus-1

 
 
 

raytracing lenses: fake?

Post by Atomic Sku » Sun, 07 Jun 1998 04:00:00




>> Other effects are, no reflecting a light beam in a mirror and no radiosity
>> effect as secondary reflections lose their luminosity and raytracing uses
>> straight lines for reflections and don't take into account diffuse materials
>> which would normally spread any light hitting them.

>> There are only a couple of renderers which can do this stuff.... none of
>> them cheap or quick.

>None of them are cheap AND quick, but if you have enough time to learn the
>program, Blue Moon Rendering Tools is very cheap (I think it's still only $20)
see
>http://www.seas.gwu.edu/student/gritz/bmrt.html

>--
>Jeremy Birn
>3dRender.com: http://www.3dRender.com/
>--

   It probably depends on what the programmer's priorities are..  ie what they
_personally_ think is most important in the rendering engine.

--
                             -=Atomic Skull=-

     See my 3-D anime character page, www.ns.net/~Argus-1

 
 
 

raytracing lenses: fake?

Post by aka MCC goodgu » Mon, 08 Jun 1998 04:00:00





> >> Other effects are, no reflecting a light beam in a mirror and no radiosity
> >> effect as secondary reflections lose their luminosity and raytracing uses
> >> straight lines for reflections and don't take into account diffuse materials
> >> which would normally spread any light hitting them.

> >> There are only a couple of renderers which can do this stuff.... none of
> >> them cheap or quick.

> >None of them are cheap AND quick, but if you have enough time to learn the
> >program, Blue Moon Rendering Tools is very cheap (I think it's still only $20)
> see
> >http://www.seas.gwu.edu/student/gritz/bmrt.html

> >--
> >Jeremy Birn
> >3dRender.com: http://www.3dRender.com/
> >--

>    It probably depends on what the programmer's priorities are..  ie what they
> _personally_ think is most important in the rendering engine.

> --
>                              -=Atomic Skull=-

>      See my 3-D anime character page, www.ns.net/~Argus-1

  So far there is no usefull export plugin for Blue Moon Rendering
Tools.  It uses the RIB format, and kinda sucks in NT, better use the
linux version if you can.  And the only LW to RIB program i found is
still in development.
 
 
 

raytracing lenses: fake?

Post by Bill and Joi Ram » Wed, 10 Jun 1998 04:00:00


If I remember correctly, according to something on the Blue Moon or
Okino web site, Polytrans and/or NuGraf will translate RIB to LWO.

On Sun, 07 Jun 1998 14:59:14 -0700, "mcooney (aka MCC goodguy1)"





>> >> Other effects are, no reflecting a light beam in a mirror and no radiosity
>> >> effect as secondary reflections lose their luminosity and raytracing uses
>> >> straight lines for reflections and don't take into account diffuse materials
>> >> which would normally spread any light hitting them.

>> >> There are only a couple of renderers which can do this stuff.... none of
>> >> them cheap or quick.

>> >None of them are cheap AND quick, but if you have enough time to learn the
>> >program, Blue Moon Rendering Tools is very cheap (I think it's still only $20)
>> see
>> >http://www.seas.gwu.edu/student/gritz/bmrt.html

>> >--
>> >Jeremy Birn
>> >3dRender.com: http://www.3dRender.com/
>> >--

>>    It probably depends on what the programmer's priorities are..  ie what they
>> _personally_ think is most important in the rendering engine.

>> --
>>                              -=Atomic Skull=-

>>      See my 3-D anime character page, www.ns.net/~Argus-1

>  So far there is no usefull export plugin for Blue Moon Rendering
>Tools.  It uses the RIB format, and kinda sucks in NT, better use the
>linux version if you can.  And the only LW to RIB program i found is
>still in development.

 
 
 

raytracing lenses: fake?

Post by L.D » Thu, 11 Jun 1998 04:00:00


Another cheap program that really copy the comportment of light
through lens : PovRay. But the interface is ...:-( It's a language to
learn PovRay. But the results are very similar to the real life in
these situations.

On Fri, 05 Jun 1998 16:53:17 +0200, William Li


>hello lightwavers,

>i am trying to raytrace light (using pointlights or distant lights) on a
>surface through a lens.
>any refraction seen directly from the camera through the lens is ok.
>but i get the feeling that light that passes through the lens and hits
>an underlying surface is just the result of filtering the affected
>surface with a (color) factor. i mean: no raytracing.

>e.g. with real raytracing light through a convex lens would converge.
>this is why you can start a fire with a looking glass in the sun. this
>is why you get that strange pattern underwater (which needs extreme
>amounts of time and power to raytrace of course) and the 'dancing
>lights' in the shadow beneath your wineglass on the table .

>concave lenses are not a problem since they disperse lightrays. the
>raytraced result would usually just look like how lw is doing it right
>now.

>am i right about the 'half-fake' raytracing (or am i imagining things)?
>if i'm right, does anyone have any ideas to simulate the light
>convergence through glasses (with/without liquid) or lenses?

>thanks.
>william li

? Renoir 1998
 
 
 

1. Can we raytrace a "lens"?

I have been playing rather extensively with the 'rayshade' tracer, and the
new 'vort' tracer, ('vort' is a GREAT tracer.  It is the most full featured
tracer I have seen in the PD domain.)

Although I have yet to actually make a stab at it, I would like to know if
the raytracing algorithm could handle this scenerio:

        Well lighted object with a transparent 'lens' between the viewpoint
        and the object, where the 'lens' has magnifying properties.

My grasp of optics is rather weak, but it occurred to me that this would
make a very interesting experiment.  Would the resulting image have a
magnified (finer detailed) image of the original object?

In other words, can we model optic properties using the standard raytracing
model elements of transparency and refraction?

-RR

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