Topic
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.
Papers published on a yearly basis
Papers
More filters
TL;DR: Expansion of the aberration function in Zernike aberrations shows that the exact aberration functions are well described by the lowest-order Zernikes spherical aberration and coma term for all but the very highest NA values.
Abstract: Optical disks are read out by focusing a beam of high numerical aperture (NA) through the substrate. Deviations of the thickness from the nominal value result in spherical aberration; tilting the substrate results in coma. Exact analytical expressions for the rms aberration per micrometer thickness mismatch (for spherical aberration) and per degree tilt (for coma) are derived. The paraxial estimates for these sensitivities proportional to NA4 (spherical aberration) and NA3 (coma) underestimate the exact values by a factor of ~2 for the value NA = 0.85, corresponding to the new Blu-ray disk format. Expansion of the aberration function in Zernike aberrations shows that the exact aberration functions are well described by the lowest-order Zernike spherical aberration (A40) and coma (A31) term for all but the very highest NA values.
31 citations
TL;DR: A gridding-based direct Fourier method for the three-dimensional reconstruction approach that uses a weighting technique to compute a uniform sampled Fourier transform and the contrast transfer function of the microscope, which is a limiting factor in pursuing a high resolution reconstruction, is corrected by the algorithm.
31 citations
22 Dec 1989
TL;DR: In this paper, the point spread function (PSF) of an epifluorescence microscope was determined using high numerical aperture oil and water immersion lenses, with the best results obtained by constrained iterative deconvolution methods.
Abstract: Recent technological advances now make it practical to record three-dimensional data from biological specimens using fluorescence light microscopy. When three-dimensional images are collected using a conventional microscope, each observed section contains in-focus information from the parts of the sample at the focal plane and out-of-focus information from the remainder of the sample. The imaging process can be characterized as a convolution of the sample with the point spread function (PSF) of the microscope. We have experimentally determined the PSF for an epifluorescence microscope using high numerical aperture oil and water immersion lenses. Several methods for the processing of the observed data are discussed, with the best results obtained by constrainediterative deconvolution methods.
31 citations
TL;DR: Overall, use of 400 kV in combination with spot‐scan does offer important improvements in contrast levels, which can be very useful in determining the three‐dimensional structure from protein crystals.
Abstract: n-Paraffin was used as a test specimen for evaluating the relative merits of 400-kV versus 100-kV electron microscopy in recording data for electron crystallographic analysis of beam-sensitive materials. The parameter used for comparison, the relative contrast R, is the ratio of amplitudes from the computed Fourier transform of images and amplitudes from an electron diffraction pattern from the same crystal. R will thus be a measure of the contrast from an experimental image relative to that of a perfect image. Electron diffraction patterns and bright-field images were recorded at 400 kV at a specimen temperature of -167 degrees C. Using the flood-beam imaging technique the best R-value is 0.08 for all reflections in the resolution zone from 4 to 3 A. This value is equivalent to that found at 100 kV. In the resolution zone from 3 to 2A we have found R = 0.02. Using the spot-scan imaging technique, on the other hand, R was measured to be 0.42 for the reflections between 4- and 3-A resolution. This amount of relative contrast is 1.7 times that observed at 100 kV. Reflections at 3-2 A displayed an R-value of 0.05. Besides obtaining higher R-values when applying the spot-scan imaging technique at 400 kV, we observe a higher yield of images with isotropic diffraction and/or higher resolution reflections. Various contrast-attenuating factors, including the modulation transfer function of the photographic film and the cryo-holder, envelope functions for spatial and temporal coherence and lens and high-tension instabilities, the contrast transfer function and lastly the radiation damage effects, have been considered in interpreting the observed image contrast. Overall, use of 400 kV in combination with spot-scan does offer important improvements in contrast levels, which can be very useful in determining the three-dimensional structure from protein crystals.
31 citations
TL;DR: It is demonstrated that semi-quantitative structural analysis on the nanometer scale can be achieved by comparing experimental C(s)- corrected HAADF STEM images with their corresponding simulated images when the effects of the C(c) coefficient and spatial incoherence are included.
30 citations