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The Canon EF-S 18–135mm lens is a standard to short telephoto telezoom for Canon digital single-lens reflex cameras with an EF-S lens mount. The field of view has a 35 mm equivalent focal length of 29–216mm. With its 7.5× zoom range, it is placed into the superzoom category.
The object in designing a field flattening lens is to create a lens that shifts the focal points of the Petzval surface to lie in the same plane. Consider inserting a pane of glass in a focusing beam. Due to refraction, the focal point of the beam is shifted by dependent on the thickness of the glass. Thus we have a thickness as a function of ...