This page gives some basic details about the Raw Refraction Filter Render Element and how it is used in compositing.
The Raw Refraction Filter Render Element is similar to the Refraction Filter Render Element, except it is not affected by the reflection weight. The result is a solid mask showing the pure refraction color as set in the V-Ray Material's settings.
This render element is enabled through the Render Elements tab of the Render Setup window in 3ds Max, and displays its parameters in a rollout at the bottom of the window:
VRayVFB – When enabled, the render element appears as a selection in the V-Ray Frame Buffer.
Deep output – Specifies whether to include this render element in deep images.
Color mapping – Applies the color mapping options specified in the Color mapping rollout (Render Setup window > V-Ray tab) to this render element. This option is disabled by default.
Multiplier – Sets the overall intensity of the render element, where 1.0 is the standard multiplier.
Denoise – Specifies whether to denoise this render element.
The Raw Refraction Filter Render Element is useful when a precise mask is needed for refractive objects. Unlike the Refraction Filter Render Element, there is no need to clip or readjust values when pure black or white is required for the composite.