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82 Chapter 17: Rendering
If a single light object is causing the problem,
you can reduce the Energy multiplier’s value
in that light objects’
mental ray Indirect
Illumination rollout (page 2–1187)
,whichis
displayed on the Modifier panel.
• Toimprovethequalityofcaustics,gotothe
Caustics group of the
Caustics And Global
Illumination rollout (page 3–104)
and increase
the number of Samples.
• Be careful of the total number of photons
you’re emitting: a very hig h number (100,000
and above) can dramatically increase your
rendering time. Then again, for some simple
scenes, you might actually be able to set these
to 1,000,000 and st i ll render in an acceptable
amount of time.
Wa rn in g: The number of photons specified for
each light indicates the number of photons that
need to be stored for each light, not the number
of photons to be shot. This is a pretty important
distinction. If a light is pointed in a direction wh ere
thereisnosurface,thementalrayrenderermight
shoot photons forever. In the
Messages Window
(page 3–86)
, the mental ray renderer will display
warnings that no photons are being stored. To avoid
the slowdowns related to this issue, make sure that
every light points in the directi on of a surface (this
is sometimes impossible to do with omni lights).
Another way to avoid this problem is to add a big
sphere around your entire model.
Coincident Faces
When it encounters coincident faces, the mental
ray renderer can produce art ifacts, because it can’t
decide which face is nearer the camera (neither is).
To fix this, move or scale one of the objects so faces
are no longer coincident.
3ds Max Materials in mental ray
Renderings
For the most part, the mental ray renderer treats
3ds Max maps and materials the same way the
default scanline renderer does. The exceptions are
listed b elow. In general, if the mental ray renderer
does not recognize a map or material, it renders
it as opaque black.
Wa rn in g: The mental ray renderer does not necessarily
suppor t maps or materials provided as plug-ins f rom
third-party vendors. I t supports third-party maps and
materials only if the vendor has explicitly used the
mental ray S DK to add support for the mental ray format.
Unless the third-party vendor clearly specifies mental
ray support, you should assume the map or material is
unsupported, and will render as black.
See also
mental ray Renderer (page 3–77)
GettingGoodResultswithmentalrayRendering
(page 3–80)
Is sues for R efl ections and R ef r acti ons
The maps used to create reflections or refractions,
Flat Mirror, Raytrace, Reflect/Refract, and Thin
Wall Refraction, are supported by the mental ray
renderer. However, the mental ray renderer simply
usesthesemapsasindicationstouseitsown
ray-tracing metho d, leading to some restrictions
on w hich parameters are supported, as descr ibed
in the sections “Materials ” and “Maps,” below.
Map Blurring
When reflections and refractions are ray traced,
applying Blur (or Distortion, in Flat Mirror)
does not apply to reflections or refract ions
of environment maps. In general, Blur and
Distortion render differently than they do with
the default scanline renderer, a nd you might have