The depth of field of an imaging system can be increased if an optical mask with a cubic phase function is placed in the principal plane of the lens [1]. The resulting image has an extended depth of field, but is of poor quality. However, the spatial frequency transfer function of the system has no nulls, and does not change with object location, or misfocus. Consequently, it is easy to digitally correct the sampled transfer function to yield an in-focus transfer function. Because this is done over a large depth of field, the combined imaging and signal processing system produces a high quality image over the entire depth of field.
The nature of extended depth of field systems can also be used to control certain aberrations. This is most easily seen through the ambiguity function of the aberrated extended depth of field system.