Rotational modulation collimators are a specialization of the modulation collimator, an imaging device invented by Minoru Oda. Devices of this type create images of high energy X-rays. Since high energy X-rays are not easily focused, such optics have found applications in various instruments. RMCs selectively block and unblock X-rays in a way which depends on their incoming direction, converting image information into time variations. Various mathematical transformations can then reconstitute the image of the source.