The Modulation Transfer Function (MTF) of an imaging device is a strong indicator of the resolution limited performance. The MTF at the system level is commonly treated as separable, with the optical MTF multiplying the postoptic (detector) MTF to give the system MTF. As new detector materials and methods have become available, and as the manufacturing of detectors has been separated from the optical system, independently measuring the MTF of the detector is of great interest. In this correspondence, a procedure for measuring the post-optic MTF of a mid-wave (3-5 micron) sampled imager is described. This is accomplished through a careful measurement of a reference optic that is later installed to allow for a final system MTF measurement. The key finding is that matching the chromatic shape of the illumination between the optic and system MTFs is critical, as in both measurements the effective MTF is scaled by the source and detector spectral shapes. This is most easily accomplished through the use of narrow bandpass filters. Our results are consistent across bandpass filter cut-on and F/number.
The MONTAGE program sponsored by the Microsystems Technology Office of the Defense Advanced Research
Projects Agency (DARPA) resulted in the demonstration of a novel approach to designing compact imaging systems.
This approach was enabled by an unusual four-fold annular lens originally designed and demonstrated for operation
exclusively in the visible spectral band. To accomplish DARPA's goal of an ultra-thin imaging system, the folded optic
was fabricated by diamond-turning concentric aspheric annular zones on both sides of a CaF2 core. The optical
properties of the core material ultimately limit the operating bandwidth of such a design. We present the latest results of
an effort to re-engineer and demonstrate the MONTAGE folded optics for imaging across a broad spectral band. The
broadband capability is achieved by taking advantage of a new design that substitutes a hollow core configuration for the solid core. Along with enabling additional applications for the folded optics, the hollow-core design offers the potential of reducing weight and cost in comparison to an alternative solid-core design. We present new results characterizing the performance of a lens based on the new design and applied to long-wave infrared imaging.
Using measured quantities, it is possible to arrive at a reasonable approximation for the optics MTF of a
longwave undersampled imaging system. Certain reasonable assumptions concerning the format of the data
from the imaging system should be made in order to make sure that there is no image processing artifacts. For
systems that contain imaging artifacts, such as an analog output, there are too many secondary effects that will
degrade the predicted Optics MTF beyond a reasonable approximation.
The objective of this study was to determine the suitability of Topas cyclic olefin copolymers (COC) as an optical plastic for use in military-grade night vision goggle (NVG) lens objectives. Test objective lenses that could include either a Topas COC window element or BK7 glass window element were manufactured. The test objectives were evaluated for low light resolution, MTF, off-axis veiling glare, and on-axis stray light. Additionally, the spectral transmittance of the individual windows elements was measured. This paper compares the evaluation results of test objectives containing Topas COC with test objectives containing BK7 glass.