The perfect combination of size and performance the pentax 40mm f28 xs da lens is a lightweight ultra thin prime lens with pentax sp super protect coating to ensure optimum picture quality at all times this pentax kaf mount lens is compatible with current and past k mount cameras and offers a focal length of 61mm in 35mm film terms this compact lens is equipped with a maximum f28 aperture which makes it ideal for low light photography portraiture and creative depth of field applicat