An imaging system comprising: a positionable device configured to axially shift an image plane, wherein the image plane is generated from photons emanating from an object and passing through a lens; a detector plane positioned to receive the photons of the object that pass through the lens; and a computer programmed to: characterize the lens by a pupil function; acquire two or more elemental images of the object with the image plane of each elemental image at different axial positions with respect to the detector plane; determine a focused distance of the object from the lens, based on the characterization of the lens and based on the two or more elemental images acquired; wherein the determination comprises to calculate a first function result of the pupil function being dependent on a first focal length and the distance of the object from the lens that corresponds with the first elemental image; to calculate a second function result of the pupil function being dependent on a second focal length and the distance of the object from the lens that corresponds with the second elemental image; to determine a ratio of the first value of the function and of the second value of the function; and to minimize a difference between: the ratio of the first function result and the second function result; and a power spectrum ratio between the first elemental image and the second elemental image; wherein the difference is minimized by mathematically searching for the distance from the object to the lens that achieves the minimization; and generate a depth map of the object based on the determined distance. a positionable device configured to axially shift an image plane, wherein the image plane is generated from photons emanating from an object and passing through a lens; a detector plane positioned to receive the photons of the object that pass through the lens; and a computer programmed to: characterize the lens by a pupil function; acquire two or more elemental images of the object with the image plane of each elemental image at different axial positions with respect to the detector plane; determine a focused distance of the object from the lens, based on the characterization of the lens and based on the two or more elemental images acquired; wherein the determination comprises to calculate a first function result of the pupil function being dependent on a first focal length and the distance of the object from the lens that corresponds with the first elemental image; to calculate a second function result of the pupil function being dependent on a second focal length and the distance of the object from the lens that corresponds with the second elemental image; to determine a ratio of the first value of the function and of the second value of the function; and to minimize a difference between: the ratio of the first function result and the second function result; and a power spectrum ratio between the first elemental image and the second elemental image; wherein the difference is minimized by mathematically searching for the distance from the object to the lens that achieves the minimization; and generate a depth map of the object based on the determined distance. characterize the lens by a pupil function; acquire two or more elemental images of the object with the image plane of each elemental image at different axial positions with respect to the detector plane; determine a focused distance of the object from the lens, based on the characterization of the lens and based on the two or more elemental images acquired; wherein the determination comprises to calculate a first function result of the pupil function being dependent on a first focal length and the distance of the object from the lens that corresponds with the first elemental image; to calculate a second function result of the pupil function being dependent on a second focal length and the distance of the object from the lens that corresponds with the second elemental image; to determine a ratio of the first value of the function and of the second value of the function; and to minimize a difference between: the ratio of the first function result and the second function result; and a power spectrum ratio between the first elemental image and the second elemental image; wherein the difference is minimized by mathematically searching for the distance from the object to the lens that achieves the minimization; and generate a depth map of the object based on the determined distance. to calculate a first function result of the pupil function being dependent on a first focal length and the distance of the object from the lens that corresponds with the first elemental image; to calculate a second function result of the pupil function being dependent on a second focal length and the distance of the object from the lens that corresponds with the second elemental image; to determine a ratio of the first value of the function and of the second value of the function; and to minimize a difference between: the ratio of the first function result and the second function result; and a power spectrum ratio between the first elemental image and the second elemental image; the ratio of the first function result and the second function result; and a power spectrum ratio between the first elemental image and the second elemental image; wherein the difference is minimized by mathematically searching for the distance from the object to the lens that achieves the minimization; and generate a depth map of the object based on the determined distance.