POV-Ray : Documentation : Camera Ray Perturbation
  POV-Ray 3.6 Documentation Online View Focal Blur Camera Identifiers Camera Ray Perturbation

The optional normal may be used to assign a normal pattern to the camera. For example:

   location Here
   look_at There
   normal { bumps 0.5 }

All camera rays will be perturbed using this pattern. The image will be distorted as though you were looking through bumpy glass or seeing a reflection off of a bumpy surface. This lets you create special effects. See the animated scene camera2.pov for an example. See "Normal" for information on normal patterns.

More about "normal" Focal Blur Camera Identifiers

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