Extended depth of field optical systems

A method for increasing the depth of field of an optical system that processes incoherent light, said optical system having an optical transfer function, said optical system having a lens for focusing incoherent light that is received from an object into an image plane, and having storing means for storing an electrical representation of the light that is incident at said image plane, said method comprising the steps of:

• constructing an optical phase mask which comprises at least a depth of field increasing feature and which alters the optical transfer function of the optical system such that the altered optical transfer function is substantially insensitive to the unknown distance between the object and the lens over a greater range of object distances than was provided by the unaltered optical transfer function;
• said mask operating to affect the phase of light that is transmitted by said mask, while having little or no effect on the intensity of light that is transmitted by said mask, and said mask depth of field increasing feature providing an altered optical transfer function that does not contain zeros within at least one bandwidth of the incoherent light;
• placing said mask between the object and the storing means;
• and
• providing depth of field post-processing for processing the stored representation of the incident light image to restore the stored light image by reversing the alteration of the optical transfer function accomplished by the mask.

A method for increasing the depth of field of an incoherent optical system having an optical transfer function, the optical system having a lens for focussing incoherent light that is received from an object into an image plane, and having storing means for storing a representation of the light that is incident at the image plane, the method comprising the steps of:

• constructing an optical mask which alters the optical transfer function of the optical system such that the altered optical transfer function is substantially insensitive to the distance between the object and the lens over a greater range of object distances than was provided by the unaltered optical transfer function, the mask constructing step including examining the ambiguity functions of a plurality of candidate mask functions to determine which particular mask function has an optical transfer function that is closest to constant over a range of object distances, and constructing the optical mask having the mask function of the particular candidate;
• placing the optical mask between the object and the storing means;
• and
• providing depth of field post-processing of the stored representation of light incident at the image plane, to thereby reverse the alteration of the optical transfer function accomplished by the optical mask.