A supplementary infrared optical system has been developed at the National Physical Laboratory (NPL) to attach to a far-focus wide-angle telescope supplied for use with a TICM II thermal imager. It uses just two germanium lenses, of 75 mm and 90 mm diameter, and allows object distances from infinity down to 0.27 m. When combined with the high quality telescope and the scanner optics, the complete system has no discernible field curvature at any working distance, an important requirement for the NPL application of measuring the spatial distribution of emissivity of extended flat surfaces. The geometrical MTF data computed for 32 combinations of object distance, field angle and aperture plane show that under most conditions the effect of aberrations is significantly less than that of diffraction. In fact spatial resolution is ultimately limited by the diffusion spread in the detector, and the performance of the optical system is always fully adequate for the 512 x 512 pixel image processing involved.

Date Published: 1 May 1986
PDF: 7 pages
Proc. SPIE 0590, Infrared Technology and Applications, (1 May 1986); doi: 10.1117/12.951963

Published in SPIE Proceedings Vol. 0590:
Infrared Technology and Applications
Lionel R. Baker; Andre Masson, Editor(s)