Calibration of defocus blur for zoom lenses

Depth from defocus(DFD) measures defocus blur, which determines the point spread function (PSF) of an image formation system. Most DFD research has been investigated with a fixed focal length, where two or more defocus images are obtained with different image distances or lens apertures. To apply DFD techniques using a zoom lens, extensive calibration of the image formation system is needed. This work presents a simple calibration technique of defocus blur for a zoom lens system. We derive the relationship of defocus blur with respect to different focal lengths of the lens. The proposed technique is applied to a spatial domain DFD technique for error analysis.