Arnold for Maya refractive caustics

Maya 2018 | Arnold 5

An account of the drastic measures that need to be taken in order to ‘persuade’ Arnold for Maya to render refractive caustics.

  1. In the refractive object’s shape attributes,
    Under ‘Arnold’, ‘Opaque’ must remain checked.
    * This is unintuitive but when refractive caustics are calculated there is no need for transparent shadows. the caustics pattern is in fact the light refracting through the object.
  2. The refractive object’s aiStandardSurface shader must have it’s Transmission layer active.
    For a colored refractive object, Transmission Weight should be 1.0,
    A color should be selected, and the density of the color should be controlled with the Depth attribute (higher values make the color less dens).
    In the shader’s advance attributes, check ‘Caustics’.
    In the shader’s Specular layer, set the IOR to match your material.
    * The default of 1.52 is the IOR for glass, and water would be IOR 1.33 for example.
  3. For refractive caustics to be rendered, the light source must be an Arnold Mesh Light,
    And in its shape attributes, under Light Attributes ‘Light Visible’ must be checked.
  4. In many cases, in order for the caustics pattern’s intensity to be correct,
    The ‘Indirect Clamp Value’ must be raised in Render Settings > Arnold Renderer, under Clamping.
  5. In some cases the Transmission value under Ray Depth in Render Settings > Arnold Renderer must be increased for the caustics to render properly.
    * Light simulation must be able refract through all the relevant surfaces.
  6. To increase the caustics render quality, the number of Diffuse samples must be raised in Render Settings > Arnold Renderer.
    * This may be unintuitive, but the caustics pattern is actually part of the Diffuse rendering of the surface upon which the caustics are appearing.

That’s it!
Hope you find this useful 🙂





Cycles Light (Shadow) Sampling

Blender 2.79

By default, in Path Tracing Integrator Mode, Cycles traces one ray randomly between all lights (per each camera – AA sample).
So if some lights in the scene are more important than others this will cause inefficient light sampling.
* Especially if there are a few important lights and many unimportant ones.

Light sampling can be set per light by switching the Integrator Mode to Branched Path Tracing, making sure Sample All Direct Lights is checked, and the setting the number of samples per light in the light parameters.
* The option to set the number of samples at the light parameters is only available in Branched Path Tracing Mode.


In the example below there are 3 lights.
The light on the right has 64 a samples per AA sample, while the 2 other lights have just 1 sample.


More on Cycles sampling:

Animating the sample settings in Cycles

Blender 2.79

A quick Cycles rendering tip:

There are situations in which we need to render an animation with changing lighting complexity, and as a result, parts of the animation need more samples than others to be effectively rendered.
For example when the camera starts it’s movement on the outside in an exterior scene, and moves into an interior space like house or a cave, or a vehicle, in many cases, the exterior part of the animation can be rendered with much less samples than the interior part.

In such cases, rendering the whole animation with the higher sample settings will demand unneeded render time in the simpler parts of the animation.

One possible solution would be to simply render the animation in two separated render jobs with different sampling settings, one for the less demanding part and another for the more complex part and than append the two parts in an editing / compositing software. but that requires more work on the shot, more management etc.

A simple solution is to animate the sample settings in Cycles.
Make tests at different times along the animation to determine how many samples are needed at each part, and key-frame the settings accordingly.


HDRI / Environment Sampling in Blender

Blender 2.79

Improve HDRI sampling by increasing the MIS (Multiple Importance Sampling) map resolution in World > Settings


When the Sampling method is ‘Branched Path Tracing’ the environment sampling isn’t found in the general Sampling Settings but in World > Settings.


* The Sampling Method can be chosen in the Render > Sampling settings


Arnold for Maya Depth of Field (DOF)

Maya 2018 | Arnold 5


  1. In the camera shape node’s Arnold Attributes:
    Check ‘Enable DOF’.
  2. Set ‘Aperture Size’ and ‘Focus Distance’ to control the effect.
    The Aperture Size attribute isn’t an f-number aperture like we would expect in photography but a radius in world units.
    Larger Aperture Size values (larger lens Iris opening), and shorter Focus Distances will cause a narrower Depth of Field which will result in the background appearing more blurry.
    DOF is generally more apparent with ‘long lenses’ (shorter focal length).
  3. Set other Aperture attributes like the number of blades and aspect ration to further design the appearance of out of focus areas and especially highlights.
    * The optical effect referred by the term ‘Bokeh’ in photography.


Related Posts:

Arnold for Maya Motion-Blur

After Effects Camera Lens Blur