Based on Cook et al '84 "Distributed Ray Tracing"
Single Sphere - 1 ray/px
Single Sphere - multiple rays/px
Motion Blur - 1 ray/px
Motion Blur - multiple rays/px
Soft Shadows - 1 ray/px
Soft Shadows - multiple rays/px
Depth of Field - 1 ray/px
Depth of Field - multiple rays/px
Depth of Field - multiple rays/px