1. A method of obtaining distance data from an object to a lens based on an image of the object obtained by an image input unit which forms an image of the object through the lens on an image receiving plane, comprising the steps of: providing a single image input unit, including a lens and an image receiving plane, obtaining two images Is and Is' of an object by forming the two images Is and Is' through the lens on the image receiving plane; obtaining the two images Is and Is' having two different first and second blurs, respectively, using said single image input unit, by setting at least one of a position of the lens and a position of the image receiving plane in relation to the object different for each of said two images Is and Is' by a minute distance .DELTA.z on an optical axis common to said two images Is and Is'; performing filtering processes by applying a filter to each of said two images Is and Is', thereby generating two output images Fs and Fs'; and calculating a distance a from the lens to the object based on said generated two output images Fs and Fs' according to a relation between said generated two output images Fs and Fs' and a radius s of the first blur and a radius s' of the second blur on the image receiving plane for the object at the distance a from the lens and a relation between the radius s of the first blur and a radius s' of the second blur and the distance a from the lens to the object.