An ellipsometer or polarimeter system, comprising: a source of electromagnetic radiation; a polarizer; a stage for supporting a sample; an analyzer; and a data detector; said ellipsometer or polarimeter system further comprising at least one aperture (H, APPS); characterized in that the ellipsometer or polarimeter system further comprises a first 1:1 imaging and relay system and a second 1:1 imaging and relay system (IS'), provided at locations selected from the group consisting of both between said source and said stage, both between said stage and said data detector, and one before and one after said stage; in that each 1:1 imaging and relay system (IS, IS') comprises a first flat mirror (FM, FM1), a concave spherical mirror having at least one concave spherical surface and a convex spherical mirror having at least one convex spherical surface; in that the 1:1 imaging and relay systems (IS, IS') are arranged such that, in use, electromagnetic radiation originating from the source passes through one of the at least one aperture and is directed to pass through the first 1:1 imaging and relay system and then subsequently through the second 1:1 imaging and relay system (IS'); in that each 1:1 imaging and relay system is arranged such that electromagnetic radiation from said aperture is caused to approach the first flat mirror and reflect therefrom on to a first location of a concave surface of the concave spherical mirror, reflects therefrom onto a convex spherical surface of the convex spherical mirror, and reflects therefrom onto a second location of the concave surface of the concave spherical mirror from which it exits the 1:1 imaging and relay system; in that the propagation direction of electromagnetic radiation entering and exiting each of said first and second imaging and relay systems is substantially unchanged by passing therethrough; and in that the first 1:1 imaging and relay system is arranged such that electromagnetic radiation passing therethrough defines a plane that is oriented 90 degrees to a plane defined by electromagnetic radiation passing through the second 1:1 imaging and relay system (IS') so as to minimize effects on a polarization state of the electromagnetic radiation passing through the 1:1 imaging and relay systems (IS, IS'). a source of electromagnetic radiation; a polarizer; a stage for supporting a sample; an analyzer; and a data detector; said ellipsometer or polarimeter system further comprising at least one aperture (H, APPS); characterized in that the ellipsometer or polarimeter system further comprises a first 1:1 imaging and relay system and a second 1:1 imaging and relay system (IS'), provided at locations selected from the group consisting of both between said source and said stage, both between said stage and said data detector, and one before and one after said stage; in that each 1:1 imaging and relay system (IS, IS') comprises a first flat mirror (FM, FM1), a concave spherical mirror having at least one concave spherical surface and a convex spherical mirror having at least one convex spherical surface; in that the 1:1 imaging and relay systems (IS, IS') are arranged such that, in use, electromagnetic radiation originating from the source passes through one of the at least one aperture and is directed to pass through the first 1:1 imaging and relay system and then subsequently through the second 1:1 imaging and relay system (IS'); in that each 1:1 imaging and relay system is arranged such that electromagnetic radiation from said aperture is caused to approach the first flat mirror and reflect therefrom on to a first location of a concave surface of the concave spherical mirror, reflects therefrom onto a convex spherical surface of the convex spherical mirror, and reflects therefrom onto a second location of the concave surface of the concave spherical mirror from which it exits the 1:1 imaging and relay system; in that the propagation direction of electromagnetic radiation entering and exiting each of said first and second imaging and relay systems is substantially unchanged by passing therethrough; and in that the first 1:1 imaging and relay system is arranged such that electromagnetic radiation passing therethrough defines a plane that is oriented 90 degrees to a plane defined by electromagnetic radiation passing through the second 1:1 imaging and relay system (IS') so as to minimize effects on a polarization state of the electromagnetic radiation passing through the 1:1 imaging and relay systems (IS, IS').