The 5 mm Aperture Mask is an aluminum disc 8.75 inches in diameter. Its center aperture is 0.196 inches in diameter. It is one of three masks that ship with the Variable Angle Specular Reflectance Accessory (01860954). It is used on the accessory's second sample stage, opposite the stage for high-angle measurements, and allows you to study a small area of a larger sample.
The Variable Angle Specular Reflectance Accessory can obtain the spectrum of any flat, reflecting surface on a plate or sheet material. Measurements of reflectance are useful for both quality control of optical materials and for obtaining information about the crystalline structure of a material. It measures reflectance spectra at angles of incidence between 15° and 80° FT-IR. This accessory is compatible with the Spectrom 3/Frontier spectrometer.