Blurred Reflections and Refractions (Frosted Glass)

Blurry reflections and refractions are normally hardly to achieve. One common way to do them with 3dsMax is by using a very fine grain noise as bump map. This usually doesn’t give a satisfying result, so this tutorial will give you a method to do (nearly) correct blurred reflection and refraction in 3dsMax.

Blurred reflections

We will start with blurred reflections. Create some convenient test scene (sphere on checkered plane, whatever).

To get the results we want we will use the raytracing antialiaser of 3dsMax on a per-material basis. So we first have to enable it globally, by opening the dialog which can be found at “Rendering” --> “Raytracer settings…”:

As we do not want to have the reflection blurred in every raytraced material we use, we disable all settings we don’t want to have (on a global level):

Click to enlarge

This done, we switch over to the material settings. Create a raytrace material and make it fully reflective. Assign it to your test object.

Now open the "Raytracer Controls" of this material. Switch the "Raytraced Reflection and Refraction Antialiaser" from "Use Global Antialiasing Settings" to "Multiresolution Adaptive Antialiaser".

Open the settings from the "…"-button. Now disable the adaptive part of the antialiaser as it will cause artefacts. To achieve this, set the threshold down to 0.0 and the initial and max rays to 128. The value for initial and max rays heavily depends on the amount of blur you are going to use (we use an amount of blur of 10.0 and a defocusing of 1.0 in this example). So if your reflections look not as smooth as they should, increase the value here.

Hit render and you should get a result like in the following image:

Experiment with the blur and defocusing amount to get the effect you are looking for.

Blurred Refraction (Frosted Glass)

Blurred refraction (or frosted glass) will be done in the same way like we did the blurred reflections. Again, enable the global antialiaser and a raytraced material. This time, leave the reflections set to zero but enable the transparency of the material. You can combine it with reflection later but for now we only care about the refraction.
Again, open the antialiaser settings in the raytracer controls. We do not need such a large blur amount for the refraction as we did for reflection, so set the blur and defocusing to 0.05 and initial and max rays to 64.

Assign the material and render:

This gives a nice blurry refraction, but if we aim for frosted glass we need to add the effect of light scattered inside the material. To do this, we will use "Falloff end distance" for refraction in the raytracer controls:

This gives a result like this:

Using the map slots

As you might have noticed, blurring and defocusing both have map slots to control them. This gives you the ability to control those parameters on a per-pixel basis from a greyscale texture.

Experiment with it, it can give really nice results!