no matter what i try, i can never get a nice diffuse reflection using mental ray. does anyone have any tips on how to achieve a nice smooth (not grainy) reflection using mental ray?

any suggestions would be great as i have been struggling with this for years.

3ds Max Design 2010/11/12, 64bit, Boxx technologies, dual quad core 2.8, nvidia quadro 4000, 20GB Ram, use mental ray for rendering, windows XP pro 64bit

Two things need to be taken into account and this is based on using a mental ray Arch & Design material where you can directly control the glossiness.  First is the glossy samples and second is the sampling quality.  You can increase the glossy samples in the material to produce smoother diffuse reflections but it is limited by the overall sampling quality in the Render Setup dialog.  You will need to play with both and do some test renders until the smoothness meets your requirements and do expect it to take longer to render.  You could always increase the Glossy Reflections Precision (Multiplier) in the Render Setup dialog as well but this increases the precision on everything in the scene and can cause unexpectedly large increases in render times.

Stephen

yeah, thats what i figured, i can set it to 128 samples and the rendering samples to 4 / 16 but i still cant get good results, i think it might have to do with having the MR sky in the environment slot and there being to high of a contrast in the reflection itself. or could be something i am overlooking.

just a thought, not sure if i am going in the right direction.

any more suggestions?

3ds Max Design 2010/11/12, 64bit, Boxx technologies, dual quad core 2.8, nvidia quadro 4000, 20GB Ram, use mental ray for rendering, windows XP pro 64bit

There are different ways of dealing with it depending on the type of scene/object you are working with.
If the reflections on you object are mostly from the environment then the Env Blur shader is a good way to get smooth reflections fast. But it’s not much use if most of the reflections come from other objects.
Fast interpolate can work in some cases, but it is not good for curved surfaces or animations. I rendering stills and your object suface is fairly flat, it may be an option.
If your object is not highly reflective then the FG and Highlight only option may work for it.
Other than that you are looking at using crazy, high sampling settings and suffering slow renders.
Another possibility is to render out an environment map of the scene using the Wraparound shader and a camera in the object’s position, then apply that locally to the material’s Env slot through the EnvBlur shader.

Can you post a sample image showing the area with the problem?

Stephen