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Did I understand the answer in this post correctly? It says that due to the fact that volumetric lighting is not implemented yet, creating a transparent laser focus with visible molecular spheres in it is not possible?

Right now I'm trying to see a sphere in a red "focus" and do not get the result I would like to have.

A sphere in a very transparent focus

Screenshot of the properties:

now with more information

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  • $\begingroup$ If you want to actually see "little spheres" you might be able to try a particle system $\endgroup$ – gandalf3 Oct 15 '13 at 22:15
  • $\begingroup$ I saw particle systems and did not try. So I may give it a try. Right now I experiment with transparency and do not get transparent effects. I add a bit more to the question... $\endgroup$ – Stefan Bollmann Oct 15 '13 at 22:19
  • $\begingroup$ The point is not, that they need to be "little" spheres. They only have to be so small that they can "diffuse" through the ray of light. $\endgroup$ – Stefan Bollmann Oct 15 '13 at 22:24
  • $\begingroup$ Related: blender.stackexchange.com/questions/1096/… $\endgroup$ – gandalf3 Oct 15 '13 at 22:28
  • $\begingroup$ Do you want to do this in cycles or BI? $\endgroup$ – gandalf3 Oct 15 '13 at 22:29
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BI:

BI does have volumetric rendering, so you could you could use two Spot lamps with Halo enabled to get this effect:

  1. ShiftA>Add > Lamp > Spot

  2. Select the spot lamp and duplicate it with AltD to duplicate linked. This way all settings will be mirrored between each Linked Duplicate.

  3. Rotate the duplicated lamp 180° (R180):

    enter image description here

  4. Enable Halo in Object Data > Spot Shape.

Note that to get volumetric shadows, Step will have to be set to 1 or higher:

enter image description here

Result:

enter image description here

Cycles:

Cycles does not yet have volumetrics integrated, but they are planned to be in 2.69 or 2.70:

Plans

For 2.68, the following features are planned to be worked on:

  • Hair shader
  • Ubershader (combined diffuse+glossy+transparent node)
  • Look into of improvements for SSS, AO, mist, ..

After this the next big feature will be Volumetrics. Probably the first release with Volumetrics will be 2.69 or 2.70.

You could fake this in Cycles by using the same scene with two spot lamps, but with transparent cone objects along with spot lamps to act as the volume.

  1. Add a Cone and match it to the shape of the spot lamp:

    enter image description here

  2. Create a material for the cones. The IsCamera ray node mixes the transparent shaders so that the cone appears to have some color only to the camera. All other rays will just pass through it unaffected. The Layer Weight node allows us to change the color based on how much faces point towards the camera.

    enter image description here

Result:

enter image description here

Note that with this technique it is impossible to get volumetric shadows. (see this post for some tricks to fake volumetrics in cycles with shadows.)

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