SPECTROPHOTOMETER

PURPOSE:To reduce the measuring error to the minimum and to precisely measure an absolute reflection factor by a method wherein an optical path length in which all sizes between corresponding mirrors are equal to the total length of an optical path for baseline measurement to be the standard is installed and the individual mirrors are arranged in such a way that light-reflecting angles become equal. CONSTITUTION:An optical path in the measurement of a baseline is passed through mirrors B, C, D, E, Q. When a sample is measured, the sample is set in a position S, the mirror C is replaced by a mirror C', the mirror D is replaced by a mirror D', and the mirror E is turned and changed over the to a mirror E'. Consequently, the optical path is passed through the mirror B, the position S and the mirrors C', D', E', Q. Here, optical path lengths are arranged as follows: S, C = S, C'; C, D = C', D'; and D, E = D', E', and angles are arranged as follows: a = a'; b = b'; and c = c'. Thereby, a completely symmetrical optical system is constituted, and measuring error due to the imbalance of the optical system is eliminated. In addition, since the optical system is completely symmetric, the spread of light can be suppressed, without destroying the balance of the optical system even when spherical mirrors are used for the mirrors C, D.