Chromatic Focal Shift Research Articles

Optimal Depth Estimation from a Single Image by Computational Imaging Using Chromatic Aberrations / Optimale Tiefenschätzung in einer Einzelaufnahme mittels Computational Imaging anhand chromatischer Aberrationen

Summary We present a computational imaging approach to estimate the depth from a single image using axial chromatic aberrations. It includes a co-design of optics and digital processing to select the optimal parameters of a lens such as focal length, f -number, and chromatic focal shift according to the performance of a depth estimation algorithm on the digital side. A simulation framework evaluates the complete systems performance in different imaging conditions including optimal axial chromatic lens aberration. A low-complexity algorithm estimates the depth map of real scenes. Experiments on real and synthetic scenes show the feasibility of the proposed system for depth estimation. In the case of relatively broadband object spectra and a lens with focal length of 4 mm, depth is estimated with an RMS error of 6-10%.

System design process for refractive simultaneous short and long wave infrared imaging

The future of optical design is multispectral imaging. Advancements in detector technology have led to the challenge of imaging over both short wave infrared and long wave infrared spectrums. This paper discusses the technical hurdles associated with designing a refractor to image over both of these spectrums, such as minimizing chromatic focal shift while maximizing contrast. The design process is outlined on an eight element F/1, 23° full field of view solution. Optomechanical design forms are evaluated by analyzing possible stresses and tolerance errors. Antireflection coating designs are discussed to complete the full system. This entire design process is highlighted as a feasibility study for the future of multispectral imaging devices.

Development of a low cost high precision fabrication process for glass hybrid asphericaldiffractive lenses

The hybrid aspherical diffractive singlet achromat design can be used to reduce chromaticaberration in compact optical systems. In this paper, the development of a compressionmolded, low cost and high precision hybrid diffractive glass lens is described. Specifically,an aspherical diffractive lens designed to compensate for chromatic aberration wasfabricated by precision glass molding. The diffractive features are integrated on theaspherical surface to avoid mold alignment during fabrication. As part of the effort to lowermanufacturing cost, the diffractive profiles were directly fabricated by single-pointdiamond turning without polishing. A thin layer of platinum–iridium coatingwas applied to the mold surfaces to protect the mold inserts from degradationduring the molding process. In order to reduce thermal shrinkage error, the hybridlens was fabricated using a two-step precision molding process on a commercialglass molding machine. The geometry of the molded hybrid aspherical diffractivelens was measured using an optical profilometer and the results demonstrated amatch to the design mold profile with a replication error of 0.16% in the radialdirection and 6.3% in the axial direction. In addition, an optical metrology system toevaluate the diffraction efficiency and chromatic focal shift was constructed andthe measured results showed that the hybrid lenses indeed function as designed.

Optical design of a line-focused forward-viewing scanner for optical coherence tomography

We report an optical design of a line-focused forward-viewing optical coherence tomography (OCT) scanner for high-speed endoscopic imaging. To avoid a complex lens system, an off-axis cylindrical mirror is used for focusing the line illumination onto the sample surface. Because of its insensitivity to the broadband spectrum, the mirror-focused scanner improves the image quality compared to a lens-focused scanner. In this work, a feasibility study is carried out on the use of a reflective-optics-focused line scanner in OCT imaging, instead of the traditional refractive optics scanner. The Strehl ratio, chromatic focal shift, and field analysis were carried out for a plano-convex cylindrical lens, an achromatic cylindrical lens, and a cylindrical-mirror-focused scanner. ZEMAX optical modeling analysis showed that mirror-focused scanning provides better Strehl ratio in comparison to plano-convex cylindrical-lens-focused scanning, and that the Strehl ratio is comparable to achromatic cylindrical-lens-focused scanning. However, field analysis on the edges of the scanning elements within the scan range shows that mirror-focused scanning is more robust when compared to a cylindrical achromatic lens. Overall, a mirror-focused scanner shows better performance compared to lenses.

Hyperspectral Shack–Hartmann test

A hyperspectral Shack-Hartmann test bed has been developed to characterize the performance of miniature optics across a wide spectral range, a necessary first step in developing broadband achromatized all-polymer endomicroscopes. The Shack-Hartmann test bed was used to measure the chromatic focal shift (CFS) of a glass singlet lens and a glass achromatic lens, i.e., lenses representing the extrema of CFS magnitude in polymer elements to be found in endomicroscope systems. The lenses were tested from 500 to 700 nm in 5 and 10 nm steps, respectively. In both cases, we found close agreement between test results obtained from a ZEMAX model of the test bed and test lens and those obtained by experiment (maximum error of 12 μm for the singlet lens and 5 μm for the achromatic triplet lens). Future applications of the hyperspectral Shack-Hartmann test include measurements of aberrations as a function of wavelength, characterization of manufactured plastic endomicroscope elements and systems, and reverse optimization.

On the Longitudinal Chromatic Aberration of the Intraocular Lenses

Primary properties of the optical materials used for intraocular lenses (IOLs) are biocompatibility and stability over time after implantation. Additionally, modern IOLs need to be flexible to be implanted through a small incision. Several compounds are usually added to existing materials (such as acrylic) to enhance the above-mentioned properties. Moreover, UV-absorbing substances are added in the IOL materials to mimic the spectral transmittance of the natural lens. Although manufacturers usually provide information for the geometry of IOLs, chromatic dispersion data are usually not available. The purpose of this study was to estimate the dispersion properties of a few materials used for IOLs. We measured the chromatic focal shift of two common types of IOLs using a simple, optical method. From the chromatic focal shift, we calculated the dispersion properties of the materials (polymethylmethacrylate and acrylic) used for the IOLs under investigation. The results deviate from the existing data in the literature for the corresponding pure materials. The presence of the UV absorber in the optical material significantly affects its dispersive properties. Longitudinal chromatic aberration (LCA) of the IOLs is approximately three times higher than LCA of the natural crystalline lens. It is expected that eyes implanted with IOLs suffer from increased LCA in comparison with intact eyes. It remains to be investigated if this increase in LCA has a significant impact on visual function.

P-72: A Chromatic Focal Shift Measurement System for 3-Panel LCOS Color Management

The chromatic focal shift (CFS) phenomenon will reduce the quality of 3-panel LCOS rear projection display system. The phenomenon is caused by the imaging position difference of different light wavelengths passing through the projection lens of rear projection display. In this paper, an instrument was designed and five auto-focus algorithms were adopted for measuring the positions of CFS. The results will be discussed and compared to each other. They will provide sufficient data to correct the back focal length when aligning the position of a panel, and then optimizing the image quality in 3-panel rear projection display, which is critical in color focusing for its high resolution.

A method for characterizing longitudinal chromatic aberration of microscope objectives using a confocal optical system

We describe a novel method of characterizing the longitudinal chromatic aberration of microscope objectives by recording a series of axial responses as a function of wavelength as a plane reflector is scanned through the focal region of a confocal microscope. Measurements are presented for a variety of objectives with differing degrees of correction. The use of the chromatic focal shift to measure surface profiles is also discussed.