[Tutorial] Creating Dust And Atmosphere in Iray

A video version is here.

I learned this method from jag11 on the DAZ3D forums, who is thanked for permission to use it in this tutorial!

In 3Delight there's no way to create atmosphere or godrays (the rays that are visible when light passes through dust or particles).  There are products to facilitate (one of them mine), but most are either not the easiest to use or ultimately just a faking of a feature the engine lacks.  Many artists use postwork instead.

DAZ Studio 4.8 Beta's new Iray engine also lacks a native mechanism for creating atmospheric volumes - but it can be easily convinced to produce them!  They will come from your lights and react to objects in your scene.  I did a test image of Jack Tomalin's Chapter House Iray scene (free to Plat Club members).

The method is:

1. Load your scene into DAZ Studio 4.8 Beta.

2.  Set the Environment to Sun and Sky in your Render Settings.

3.  Jag11 says to set time of day to 12 noon. I set it to 3 p.m. in the above test.  I think what matters is that you set the SSS direction properly for the light direction (below).

4.  Make sure that your camera headlamp is set to OFF.  This is in the camera's parameter settings; you must render through a "real" camera and not the perspective, top, right, etc. views.

5.  Create --primitive--cube.  Other shapes will probably work.  The important thing is that you scale it up large enough that your camera cannot see past its outer edges, ideally as big as your room (or if outdoors, really, really huge).  The camera must be outside the primitive. 

6.  Select the cube in Scene Tab and look at its surface in Surfaces tab.  Select the surface.  Apply the Uber Iray Base shader.  Turn OFF all the glossy settings (glossiness, glossy layered weight, etc.)

7.  Scroll down to the Refraction.  Set the amount to maximum and the index number to 1.00 (I believe it's 1.5 by default). 

8.  Scroll down to the Thin Walled setting.  Set it to OFF.

9.  Scroll down to the SSS settings.  Jag11's recommended settings are

Scattering Measurement Distance: 50
SSS Amount: .03
SSS Direction: 0.5

For the huge room in Jack's Chapter House scene, I used:

Transmitted Measurement Distance: 100 (same as the Scattering, leaving it at 0.1 produces black renders)
Scattering Measurement Distance: 100 (I reasoned that the rays needed to go further into the room)
SSS Amount: .05
SSS Direction: -0.45 (which, as it turns out, was wrong; in the version shown I've corrected it to 0.5.)

Adding a higher SSS amount will make your atmosphere more dusty.  I used an incorrect value of SSS direction at first. According to DAZ's docs, "Negative numbers (-) backscatter to the direction of the light source. Positive numbers (+) forward scatter away from the direction of the light."

Here's a scene you can use to test this, and a copy of the most successful version of the shader I used.



So really, you should always use a positive number of SSS direction for this.  This is probably why I didn't get very defined rays in my scene until the second try (the version you see for the Chapter House scene now).

In the second scene, the Park Side High Lobby, I used an HDR for fill and spotlights for lighting; there is no "Sun" light.  So that is definitely not mandatory as a lighting method to get these rays.

I look forward to your renders using this method!