Autodesk 12812-051462-9011 User Guide 3 - Page 719

This is the fastest option. You can use it if the camera and refractive object don't move. Every Nth Frame Tells the renderer to regenerate the refracted image based on the frame rate on page 7987 set by the spinner. Every single frame provides the most accurate result, but takes longest to render. Use Environment Map When off, environment maps are ignored by the refraction during rendering. It's useful to turn it this off when you have refractions in the scene and you're rotoscoping against a flat screen environment map. A screen environment map does not exist in 3D space the way the other environment map types do, and will not render properly. Default=on. Refraction group These controls are specific to the Thin Wall Refraction effect: Thickness Offset Affects the size of the refractive offset, or jog effect. At 0, there's no offset, and the object can appear invisible in the rendered scene. At 10.0, the offset is at its greatest. Range from 0.0 to 10.0; Default=0.5. NOTE The IOR (index of refraction) spinner in the parent material's Extended Parameters rollout also affects the offset effect. Bump Map Effect Affects the magnitude of refraction due to the presence of a bump map. This parameter multiplies the current bump map Amount in the parent material. Reduce this value to reduce the effect of the secondary refraction; increase this value to increase the effect. If there is no bump map assigned, this value has no effect. Default=1.0. If there is unevenness in the surface of the glass, there is a secondary refraction. Thin Wall Refraction generates this secondary refraction if the material also has a bump map present. The algorithm guesses at the scaling of the secondary refraction, and can create too large an effect. If this happens, scale the effect down by reducing this value to less than one. mental ray Shaders In mental ray, a shader is a function that calculates light effects. There can be shaders for lights, cameras (lens shaders), materials, shadows, and so on. 5974 | Chapter 19 Material Editor, Materials, and Maps