A rotating-sector attenuator has been constructed using components of readily available precision. The transmittance of the attenuator is adjustable in motion through a differential gear system and can be read from a dial with a precision of about ±0.02% of maximum transmittance. The sector has been used to measure and calibrate the photometric properties of spectrophotometers in the ultraviolet, visible, and infrared regions. It has also been used as an attenuator in an optical-null infrared spectrophotometer in place of the usual comb. Absorption spectra of typical samples have been made with a precision of ±0.04% transmittance. Transmittance and absorptivity data are presented for samples of calcium fluoride in the 700 to 1300 cm-1 spectral region.
James E. Stewart, "A Rotating-Sector Attenuator of Adjustable Transmittance for Precise Spectrophotometry," Appl. Opt. 1, 75-77 (1962)