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Caustics and Global Illumination Rollout (mental ray Renderer) 107
Inter face
Caustics group
Impor tant: For caustics to render, you must also make
sure to set up these other conditions in your scene:
• Atleastoneobjectmustbesettogenerate
caustics. This is off by default.
• At least one object must be set to receive
caustics. Thisisonbydefault.
• At least one light must be set to generate
caustics. This is off by default.
The settings for generating and receiving caustics
are located on the Object Properties dialog >
mental ray Panel (page 1–126).
Enable—When on, the mental ray renderer
calculates caustics effects. Default=off.
Multiplier/color swatch—Use these to control
the intensity and color of the indirect light
accumulated by caustics. The defaults, 1.0 and
white, produce physically correct rendering.
This is useful for adjusting the contribution of the
caustics effect, thus improving the quality of an
image.
Ma xi mum Num. P hotons per S a mple—Sets how
man y photons are used to compute the intensity of
thecaustic. Increasingthisvaluemakescaustics
less noisy but also more blurry. Decreasing this
value makes caustics more noisy but less blurry.
The larger the Samples value, the greater the
rendering time. Default=100.
Tip: To preview a caustic, set Samples to 20, then
increase the value for a final rendering.
Maximum Sampling Ra dius—When on, the spinner
value sets the size of photons. When off, each
photon is ca lculated to be 1/100 of the radius
of the full scene. Maximum Sampling Radius
default=off; va lue default=1.0.
In many cases, the default photon size
(Radius=off) of 1/100 the scene size gives useful
results. In other cases, the default photon size
mightbetoolargeortoosmall.
When photon reflections overlap, the mental r ay
renderer uses sampling to smooth them together.
Increasing the number of samples increases
the a mount of smoothing and can create more
natural-looking caustics. When photons have a
small radius and don’t overlap, the Samples setting
hasnoeffect. LowRadiusvalueswithalarge
number of photons result in dotty caustics.