Using molded chalcogenide glass technology to reduce cost in a compact wide-angle thermal imaging lens

摘要

This paper presents the design, analysis, and fabrication of a telecentric f/1.3 thermal imaging lens. The 14.8 mm wide-angle lens provides a 62° diagonal field-of-view, and was designed to operate over the 8-14μm infrared spectral band. Focus can be manually adjusted from 0.5 m to infinity, maintaining constant image quality over the entire range. A compact air-spaced doublet design limits the overall length to 34 mm and the maximum diameter to 28 mm. Lens materials were chosen to minimize chromatic aberrations, reduce cost, and fit within the molded chalcogenide glass manufacturing capabilities. Combining a molded aspheric chalcogenide lens with a polished spherical Germanium lens eliminated the need for a diffractive surface to correct chromatic aberrations, and reduced the fabrication cost. Vignetting was purposely introduced at the extreme fields to compensate for the effects of aberrations on the relative illumination variation across the field-of-view. Athermalization of the lens was achieved mechanically over the entire operating temperature range (- 40 to + 80℃).