Troubleshoot caustics don’t work or look incorrect

Blurry or noisy caustics

Do any of the following:

• Tweak Radius until there is no visible change, then Accuracy until you get the desired results.
• Work with the Caustic FilterType to sharpen or smooth caustics.

Caustics don’t work with a directional light

Don’t use directional lights for photon emission. Although you can render caustics and global illumination with a directional light source (that is, all the necessary attributes exist), we recommend against it. Because a directional light has no origin, it will unnecessarily shoot photons into a scene where they aren’t needed, thereby increasing render times dramatically.

If you must render a directional light with photon emission (with mental ray for Maya), ensure that objects are marked properly for photon tracing. For more information on photon tracing and problems that may occur, see GI photon maps vs. caustic photon maps.