10.3 Depth of Field attributes

Iray uses the default attributes coming with the default Maya camera to control Depth of Field, except Focus Region Scale.
Depth of field attributes
Depth of Field
Enables or disables Depth of Field calculation.
Focus Distance
The distance from the camera at which objects appear in sharp focus, measured in the scene's linear working unit. The valid range is 0 to infinity. The default value is 5.
F Stop
Controls the area of sharpness around the value set in Focus Distance. Larger values make this area bigger.