2008

caustics (so that caustics are scattered within the glass itself), and the
tabletop only to receive caustics (unless its chrome, say, instead of wood).
If the rendering of your scene is washed out by light, double-check the
Multiplier settings: one in the Basic group of the Final Gather rollout on
page 6104 , and one each in the Caustics and Global Illumination (GI) groups
of the Indirect Illumination panel > Caustics And Global Illumination
rollout
on page 6096 . These apply to all lights in the scene. Reducing the
Multiplier values can eliminate washout.
If a single light object is causing the problem, you can reduce the Energy
multiplier's value in that light object's
mental ray Indirect Illumination
rollout
on page 5060 , available on the Modifier panel.
To improve the quality of caustics, go to the Caustics group on page 6099
of the
Caustics And Global Illumination rollout on page 6096 and increase
the Max Num. Photons Per Sample setting.
Be careful of the total number of photons youre emitting: A very high
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 still render in an acceptable amount of time.
WARNING 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 an important distinction: If a light points in a
direction where there is no surface, the mental ray renderer might shoot
photons forever. In the
Messages Window on page 6054 , the mental ray renderer
displays warnings that no photons are being stored. To avoid the slowdowns
related to this issue, make sure that every light points in the direction 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.
In general, use an exposure control. The
mr Photographic Exposure
Control
on page 6544 works particularly well for adjusting overall exposure.
Coincident Faces
When it encounters coincident faces, the mental ray renderer can produce
artifacts, 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.
mental ray Renderer | 6047