You want to use one of the pre-defined 'lens shader' boxes. To alter the lens procedurally, you can attach one of the boxes under Patterns to the EFX input of the patterned_lens box. Patterns return floating point values which will vary the affect on the lens.

This is an example of a simple procedural lens shader:

The textured_lens box must be used with a soft_color_2D box to define a map file. This shader gives the effect that the camera lens is etched with the map image. The GAIN button is used to control the depth and direction, in or out, of the etching.

The color of the scene can be tinted by changing the GEL button to another color besides white. In this case the gel is yellow which tints the default blue ball green.

The "dof_lens" (depth of field lens) box is a SoftImage implimentation of a lens shader.