A. I'm using photons to allow light to be reflected off an object. 
However I don't seem to be able to get a perfectly straight beam of 
light. The image below is a 16u x 16u grid. The spotlight is 72u from 
the top of the grid and then is masked by the red 'turret' at the top in 
order to thin it down. This does an OK job, but as the light reflects of 
more and more objects, the wider the beam gets. Is there any way to stop 
it getting wider?

B. Once the light reflects off the first object it starts to interact 
with the media as I'd expect (the glow) however before it hits that 
first object, there is no glow! How do I get the glow on the first part 
of the beam? One solution I had was to start the beam to the left of the 
masking turret and fit a mirror into the mask, but surely there's a 
better way?

Cheers!
Rick Measham

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> A. I'm using photons to allow light to be reflected off an object. 
> However I don't seem to be able to get a perfectly straight beam of 
> light. The image below is a 16u x 16u grid. The spotlight is 72u from 
> the top of the grid and then is masked by the red 'turret' at the top in 
> order to thin it down. This does an OK job, but as the light reflects of 
> more and more objects, the wider the beam gets. Is there any way to stop 
> it getting wider?

This is probably an inaccuracy in the photon mapping. Use more photons 
and it will probably reduce the effect. (And the render speed!!)

> B. Once the light reflects off the first object it starts to interact 
> with the media as I'd expect (the glow) however before it hits that 
> first object, there is no glow! How do I get the glow on the first part 
> of the beam? One solution I had was to start the beam to the left of the 
> masking turret and fit a mirror into the mask, but surely there's a 
> better way?

Hmm... can't help you there I'm afraid. :-(

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Orchid XP v2 <43a3f2fb$1@news.povray.org> Saturday 17 of December 2005 12:14

> This is probably an inaccuracy in the photon mapping. Use more photons
> and it will probably reduce the effect. (And the render speed!!)

Or set the light source to be parralelal? (spelling)

Btw, can You Rick share source code of this sexample scene?

-- 

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High!

Raf256 wrote:
> Or set the light source to be parralelal? (spelling)

parallel!

See you in Khyberspace!

Yadgar

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Rick Measham nous apporta ses lumieres en ce 2005-12-17 04:04:
> A. I'm using photons to allow light to be reflected off an object. 
> However I don't seem to be able to get a perfectly straight beam of 
> light. The image below is a 16u x 16u grid. The spotlight is 72u from 
> the top of the grid and then is masked by the red 'turret' at the top in 
> order to thin it down. This does an OK job, but as the light reflects of 
> more and more objects, the wider the beam gets. Is there any way to stop 
> it getting wider?
> 
> B. Once the light reflects off the first object it starts to interact 
> with the media as I'd expect (the glow) however before it hits that 
> first object, there is no glow! How do I get the glow on the first part 
> of the beam? One solution I had was to start the beam to the left of the 
> masking turret and fit a mirror into the mask, but surely there's a 
> better way?
> 
> Cheers!
> Rick Measham
> 
> 
> ------------------------------------------------------------------------
> 
A. Try a parallel light.
b. Add a small transparent cylinder in the hole of the turret. It will make all of the
beam photons. 
Before the first reflection, photons are not taken into consideration, they are after
that first 
reflection. Adding the transparent cylinder, or a box, will stop the light and replace
it by the 
photons. It may not be exactly how it works, but describe what appens.

-- 
Alain
-------------------------------------------------

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Rick Measham wrote:

> A. I'm using photons to allow light to be reflected off an object. 
> However I don't seem to be able to get a perfectly straight beam of 
> light. The image below is a 16u x 16u grid. The spotlight is 72u from 
> the top of the grid and then is masked by the red 'turret' at the top in 
> order to thin it down. This does an OK job, but as the light reflects of 
> more and more objects, the wider the beam gets. Is there any way to stop 
> it getting wider?
> 
> B. Once the light reflects off the first object it starts to interact 
> with the media as I'd expect (the glow) however before it hits that 
> first object, there is no glow! How do I get the glow on the first part 
> of the beam? One solution I had was to start the beam to the left of the 
> masking turret and fit a mirror into the mask, but surely there's a 
> better way?

If you are using a spotlight to create the beam, then the widening may 
be caused by the natural dispersion of the beam.

I suspect that you might get better results by modeling the beam as a 
set of cylinders, maybe with a cylindrical light source in each.

Regards,
John

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Alain wrote:
> A. Try a parallel light.
> b. Add a small transparent cylinder in the hole of the turret. It will 
> make all of the beam photons. Before the first reflection, photons are 
> not taken into consideration, they are after that first reflection. 
> Adding the transparent cylinder, or a box, will stop the light and 
> replace it by the photons. It may not be exactly how it works, but 
> describe what appens.

Thanks Alain, worked like a charm.

Here's the latest render with the parallel lights and the transparent 
filter in the turret.

(The source will be available on my website once I've finished)

Cheers!
Rick Measham

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