We have recently installed a new sample chamber at the NIST/DARPA EUV Reflectometry Facility at the National Institute of Standards and Technology. The chamber replaces a much smaller system on Beamline 7 at the Synchrotron Ultraviolet Radiation Facility that was commissioned almost ten years ago as a dedicated facility for the measurement of normal-incidence extreme ultraviolet optics used in lithography development, astronomy, and plasma physics. The previous measurement chamber was limited to optics less than 10 cm in diameter, and, thus, we were not able to measure many of the optics used in modern telescopes and extreme ultraviolet lithography steppers. The new chamber was designed to accommodate optics up to 36 cm in diameter and weighing up to 40 kg, and with modifications will be able to measure optics up to 50 cm in diameter. It has three translation and three rotation axes for the sample and two rotation axes for the detector, with an accuracy of better than 0.5 mm in translation and 0.04o in rotation. We will describe design considerations, performance of the positioning mechanisms, and initial reflectivity measurements of both curved and flat surfaces.