Hi. I want my reflective surfaces (which are plastic) to produce a genuine fresnel effect (where reflections are only visible when the surface is viewed at an angle rather than straight-on). At the moment, I'm using the Falloff material with a Raytrace sub-material to achieve this effect, but the render times are absolutely killing me. Can someone please tell me how to achieve this with reasonable performance? I'm using mental ray as my renderer, and my materials are all Raytrace materials. (I opted for this over the mr DGS and Dielectric materials because nearly all of my objects are opaque, and I don't need any refractions.) Thanks very much for your help.

have you worked out which part of the render is killing the performance?

That's a very good point. At first I figured it was combining a Falloff map with a Raytrace map, but in retrospect it may have been my attenuation settings. I'm using a Raytrace material now, which means I can use a single Falloff map in the reflection slot to achieve basically the same results, and I have more control over raytracer settings. I'll continue working on the problem. Thanks for the tip. I'm already seeing better results.