An image sensor may include an array of imaging pixels. Each imaging pixel may have a photosensitive area that is covered by a microlens and a diffractive lens that focuses light onto the photosensitive area. The diffractive lens may be interposed between the microlens and the photosensitive area. The diffractive lens may have a higher index of refraction than the surrounding materials. The diffractive lens may be formed as a portion of an anti-reflection coating. In some cases, multiple diffractive lenses may be formed over the imaging pixels. Focusing and defocusing diffractive lenses may be used to tune the response of the imaging pixels to incident light.