An encoder system comprising: an encoder head for use with a diffractive encoder scale, wherein the encoder head comprises one or more optical components arranged to: i) direct a first incident beam to the diffractive encoder scale at a first incident angle with respect to a normal to the encoder scale; ii) receive a first return beam from the diffractive encoder scale at a first return angle with respect to the normal to the encoder scale, the first return angle being different from the first incident angle; iii) redirect the first return beam to the diffractive encoder scale as a second incident beam at a second incident angle with respect to the normal to the encoder scale; and iv) receive a second return beam back from the diffractive encoder scale at a second return angle with respect to the normal to the encoder scale, the second return angle being different from the second incident angle, wherein the one or more optical components are arranged to combine the second return beam with a reference beam to form an output beam; a detector positioned to detect the output beam; and an electronic processor configured to receive an interference signal from the detector, the interference signal comprising a phase related to an optical path difference between the reference beam and the second return beam, and to determine information about a change in position of the encoder scale based on the phase, wherein the one or more optical components comprise a beam splitting component arranged to receive a source beam from an optical source, the beam splitting component being operable to derive the first incident beam and the reference beam from the source beam, characterized in that a difference between the first incident angle and second incident angle is less than a difference between the first incident angle and the first return angle and less than a difference between the second incident angle and the second return angle. an encoder head for use with a diffractive encoder scale, wherein the encoder head comprises one or more optical components arranged to: i) direct a first incident beam to the diffractive encoder scale at a first incident angle with respect to a normal to the encoder scale; ii) receive a first return beam from the diffractive encoder scale at a first return angle with respect to the normal to the encoder scale, the first return angle being different from the first incident angle; iii) redirect the first return beam to the diffractive encoder scale as a second incident beam at a second incident angle with respect to the normal to the encoder scale; and iv) receive a second return beam back from the diffractive encoder scale at a second return angle with respect to the normal to the encoder scale, the second return angle being different from the second incident angle, i) direct a first incident beam to the diffractive encoder scale at a first incident angle with respect to a normal to the encoder scale; ii) receive a first return beam from the diffractive encoder scale at a first return angle with respect to the normal to the encoder scale, the first return angle being different from the first incident angle; iii) redirect the first return beam to the diffractive encoder scale as a second incident beam at a second incident angle with respect to the normal to the encoder scale; and iv) receive a second return beam back from the diffractive encoder scale at a second return angle with respect to the normal to the encoder scale, the second return angle being different from the second incident angle, wherein the one or more optical components are arranged to combine the second return beam with a reference beam to form an output beam; a detector positioned to detect the output beam; and an electronic processor configured to receive an interference signal from the detector, the interference signal comprising a phase related to an optical path difference between the reference beam and the second return beam, and to determine information about a change in position of the encoder scale based on the phase, wherein the one or more optical components comprise a beam splitting component arranged to receive a source beam from an optical source, the beam splitting component being operable to derive the first incident beam and the reference beam from the source beam, characterized in that a difference between the first incident angle and second incident angle is less than a difference between the first incident angle and the first return angle and less than a difference between the second incident angle and the second return angle.