Use Maya Volume Sampling - This parameter is used with mental ray only. Enable this option if you have FumeFX intersecting with geometry or you have multiple FumeFX grids and objects in the scene. When enabled, you will also need to enable the "Use Autovolume" inside the mental ray rendering options.
Samples Multiplier % - FumeFX will automatically determine optimal raymarching step size for each frame. By using this parameter, user can increase or decrease number of samples. Higher number means lower raymarching step size, better quality and longer render times.
Step Size % - This setting affects rendering quality. The selected value defines a ray marching stride based on a percentage of the voxel size. With smaller values, more steps will be needed for shading to achieve a high quality output. But, for example, you don't need to go very low for uniform and transparent smoke as there's no detail in it. You might want to use lower values in connection with Fluid Mapping usage.
Step Size In Fire % - This spinner specifically affects the rendering quality in fire. It can be linked to the default step size, or set separately if you need more accuracy in rendering fire. Due to the nature of fire, you will need a smaller step size for fire than for smoke.
Jittering % - This parameter adds spatial randomness to the sampling. With a high step size you might get noise - like effects, but with a finer step size you will gain soft, blurred smoke.
Falloff Type - This selection defines the method that will be used to attenuate smoke and/or fire near the edges of the simulation area.
Falloff Strength - This adjusts the strength of falloff.
Separate Alpha - By default, FumeFX computes alpha channel in a different way than colors and transparencies used to blend fire and smoke during ray marching. This is useful for Smoke Shader because changes in falloff values will not alter final alpha channel. It also allows for the Fire Shader to boost up alpha channel without changing final result.This however has a drawback. If you put a transparent object inside a fire, you will immediately notice rendering artifacts. In mental ray, artifacts could be visible if FumeFX grids overlap.
Motion Blur -To be able to use motion blur caches must have velocities exported.
Duration - Motion Blur duration in frames. This parameter is just the multiplier of the duration parameter from rendering dialog. Duration larger than 1 frame will result with incorrect motion blur.