Aberration Invariant Optical/Digital Incoherent Optical Systems
Imaging Systems Laboratory, Department of Electrical Engineering University of Colorado, Boulder, Colorado 80309 Aberration Invariant Optical/Digital Incoherent Optical Systems Edward R. Dowski, Jr., W. Thomas Cathey, and Joseph van der Gracht Abstract Control of optical aberrations is a principal objective of any optical design. High performance optical designs with well-corrected aberrations typically have a very low tolerance to fabrication and alignment errors and are composed of very specific optical materials. Such systems are almost always more costly than equivalent systems with less well-corrected aberrations. By optimum combination of optical pre-processing and digital post-processing, or optical coding and digital decoding of the image information, incoherent optical systems invariant to numerous aberrations can be formed. The theory of aberration invariance can also be used with low-cost, low-precision optics to produce systems that image with the performance of high-cost, high-precision, or near diffraction-limited, spatial resolution. We can show that the central aberration to be controlled is second order, or misfocus. Systems that are invariant to misfocus are also invariant to chromatic aberration, astigmatism, thermal effects, and spherical aberration. This paper therefore describes, with experimental evidence, a focus-invariant optical system. Research The most common approach to approximating a focus-invariant imaging system is to stop down the pupil aperture. Although stopping down the aperture does increase the amount of focus invariance, or depth of field, there is an attendant loss in optical power at the image plane, as well as a reduction of the diffraction-limited image resolution. The aperture can be viewed as a simple absorptive mask in the pupil plane of an optical imaging system; however, this absorptive nature results in a loss of light.
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