1. A method for efficient measurement of ensquared energy in an imaging system, the method comprising: capturing an image of a target comprising a plurality of point sources at a sensor associated with the imaging system, wherein the point sources are positioned at one of a plurality of offset positions, such that the distance, in at least one of the horizontal and vertical direction, between the center point of a first light beam projected by a first point source onto a focal plane array associated with the sensor and a center point of a second light beam projected by a second point source projected onto the focal plane array is a non-integer number of pixels that is greater than one; determining an ensquared energy value for each point source; and estimating an ensquared energy value for the imaging system from the determined ensquared energy values for the plurality of point sources.