Contrast transfer function

About: Contrast transfer function is a research topic. Over the lifetime, 934 publications have been published within this topic receiving 26533 citations.

Assessment of retinal function in cataract patients by a combination of laser interferometry and conventional display methods to measure contrast sensitivity

Abstract: Conventional methods of measuring retinal function are dependent on the optics of the eye. Therefore, an optical opacity such as a cataract that obstructs the normal optical transmission of light can prevent measurement of retinal function. In some cases a laser interferometer designed to bypass the effects of the optics of the eye may be employed to measure retinal function without interference due to the optical components. In this study we compare contrast sensitivity functions determined by laser interferometry and conventional display methods for cataract and normal eyes. Comparison of laser and monitor contrast sensitivity functions indicates that for these cataract patients interferometric measurements show a normal retinal function, whereas similar measures using the traditional display system (monitor) show considerable loss of visual function. The extent to which contrast sensitivity was limited by the lens of the eye is indicated by the ratio of laser and monitor contrast thresholds. In general, the laser interferometry technique demonstrates that relatively minor cataracts decrease the contrast transfer function of the eye' optics over a range of spatial frequencies.

Visualization of polymer interfaces by phase contrast (''defocus'') electron microscopy

Abstract: A significant problem in studies of polymer microstructure is obtaining enough contrast in electron micrographs to visualize the system Most techniques now used take advantage of amplitude changes produced by the interaction of the electron beam with the object In this paper we investigate the possibility of using phase changes induced in the electrons by the object and by microscope defocus to produce usable image contrast We use the standard linear transfer theory of microscope imaging to evaluate the images produced by several different model objects The basic structure investigated is an alternating sequence of domains These models correspond reasonably closely to the suggested microstructure of several polymer systems and the calculations should be directly applicable to them Our calculations show that for reasonable inner potential changes and film thickness usable image contrast can be obtained The technique is most sensitive to rapid phase changes and will be most successful with objects having sharp rather than diffuse domain boundaries Defocusing produces fringes at the domain boundaries with the size of these fringes depending on both the object and the amount of defocus The results indicate that defocusing is useful for polymer structure investigations However, the defocused image will not correspond directly to the object structure, and some care must be taken in deducing the true object structure

A simple method for minimizing non-linear image contrast in spherical aberration-corrected HRTEM.

Abstract: A simple and practical method for minimizing non-linear image contrast in spherical aberration-corrected (C(S)-corrected) high-resolution transmission electron microscopy is presented. The effectiveness of the method is considered from the viewpoints of theoretical formulations and image simulations including second-order imaging effects. The method is one of the advantages of C(S)-correction and applied to high-resolution images down to 0.1 nm. The dynamical diffraction effect is carefully evaluated, which shows that the phase deviation of diffracted waves from pi/2 violates the present method in thicker crystals over approximately 10 nm.

Effect of incident probe on HAADF STEM images

Abstract: Atomic-resolution incoherent high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) images of [011]-oriented Si have been recorded using different incident beam probes, and analysed by means of dynamical image calculation based on the Bloch wave description. It is shown how atomic-resolution images are influenced by the semiangle of the probe and the spherical aberration and defocus of the probe-forming lens. The resolution of an incoherent HAADF STEM image can be simply perceived by the contrast transfer function of incoherent imaging which is the Fourier transform of the incident probe intensity.