Fig. 2.

FTIR, visible images and extracted transmittance profiles of the 1951 USAF resolution target measured through the ZnS hemisphere with (a) effective aperture size of 1.3 μm × 1.3 μm with an effective step size of 0.44 μm and (b) effective aperture size of 2.7 μm × 2.7 μm with a set step size of 0.89 μm for the black and red profiles. A blue profile is also added to the plots, which represents the measurement made without the hemisphere with (a) 1 μm × 1 μm with an effective step size of 0.4 μm and (b) 3 μm × 3 μm with an effective step size of 1 μm