Showing papers on "Contrast transfer function published in 1997"
TL;DR: In this article, a simple general treatment of x-ray image formation by Fresnel diffraction is presented; the image can alternatively be considered as an in-line hologram Particular consideration is given to phase-contrast microscopy and imaging using hard x rays.
Abstract: A simple general treatment of x-ray image formation by Fresnel diffraction is presented; the image can alternatively be considered as an in-line hologram Particular consideration is given to phase-contrast microscopy and imaging using hard x rays The theory makes use of the optical transfer function in a similar way to that used in the theory of electron microscope imaging Resolution and contrast are the criteria used to specify the visibility of an image Resolution in turn depends primarily on the spatial coherence of the illumination, with chromatic coherence of lesser importance Thus broadband microfocus sources can give useful phase-contrast images Both plane- and spherical-wave conditions are explicitly considered as limiting cases appropriate to macroscopic imaging and microscopy, respectively, while intermediate cases may also be of practical interest Some results are presented for x-ray images showing phase contrast
429 citations
TL;DR: Methods to determine the CTF from experimental data and to obtain a CTF-corrected 3D reconstruction were developed, resulting in a distortion-free 3D map of the ribosome at 1/24.5 A-1 resolution.
176 citations
71 citations
TL;DR: This work proves that the clarity and precision by which the CTF can be detected using periodogram averaging and autoregressive modelling is far better than by any conventional method based on the Fourier transform amplitude alone.
61 citations
01 Jan 1997
TL;DR: In this article, a method of threedimensional (3D) reconstruction that combines an algebraic, iterative 3D reconstruction technique with CTF correction is proposed, and the potential to incorporate a priori knowledge into the reconstruction process is discussed.
Abstract: Cryo-electron microscopy provides the means to quantitatively study macromolecules in their native state. However, the original mass distribution of the macromolecule is distorted by the contrast transfer function (CTF) of the electron microscope. In addition, the zeros of the CTF put a practical limit on the resolution that can be achieved. Substantial improvement to the quality of the results can be accomplished by collecting the data using a series of defocus settings. Such data sets can be combined and the resolution can be extended beyond the first zero of the CTF. This procedure can be applied either at the stage of raw data, or more effectively at the stage of reconstructed volumes which have a high signal-to-noise ratio as a result of averaging over many projections. A method of threedimensional (3D) reconstruction that combines an algebraic, iterative 3D reconstruction technique with CTF correction is proposed. The potential to incorporate a priori knowledge into the reconstruction process is discussed. This approach was used to obtain a 3D reconstruction of the E. coli 70S ribosome from energy filtered cryo-images.
42 citations
TL;DR: In this paper, the authors derived analytical expressions for the chromatic and spherical aberration point spread functions of an electron lens, taking into account the angular distribution of inelastic scattering and energy distribution of the electrons forming the image.
37 citations
TL;DR: In this article, a modified optical system for the light microscope has been devised in order to remotely shift the focal plane and to manipulate the point spread function for any given objective lens, thus achieving high throughput three-dimensional microscopy of living specimens.
Abstract: A modified optical system for the light microscope has been devised in order to remotely shift the focal plane and to manipulate the point spread function for any given objective lens. An adjustable telescope system is inserted into the microscope tube so as to move the intermediate image position, thus achieving two goals of fundamental importance for the three-dimensional imaging of biological samples. First, it allows the focus to be rapidly varied without actually moving the objective lens. This permits high throughput three-dimensional microscopy of living specimens. Secondly, it makes possible the compensation of objective lens spherical aberration. This distortion is especially significant when high numerical aperture objectives are utilized to image deep into thick specimens.
22 citations
TL;DR: In this article, the authors discuss focusing of two-dimensional and three-dimensional scalar wave at low Fresnel numbers in the presence of cylindrical or spherical aberration.
Abstract: In this paper we discuss focusing of two-dimensional and three-dimensional scalar waves at low Fresnel numbers in the presence of cylindrical or spherical aberration. We show that a larger maximum axial intensity than in the aberration-free case can be obtained with a positive cylindrical or spherical aberration. Also, we give a physical explanation of this unexpected result.
20 citations
TL;DR: A new method is proposed for the computation of the tristimuli values that correspond to the impulse response along the optical axis provided by an imaging optical system working under polychromatic illumination that shows that all the monochromatic irradiance distributions can be obtained from the Wigner distribution function associated with a certain version of the pupil function of the system.
Abstract: We propose a new method for the computation of the tristimuli values that correspond to the impulse response along the optical axis provided by an imaging optical system working under polychromatic illumination. We show that all the monochromatic irradiance distributions needed for this calculation can be obtained from the Wigner distribution function associated with a certain version of the pupil function of the system. The use of this single phase-space representation allows us to obtain the above merit function for aberrated systems with longitudinal chromatic aberration and primary spherical aberration. Some numerical examples are given to verify the accuracy of our proposal.
12 citations
TL;DR: A negative space charge cloud can be formed to reduce the spherical aberration of a lens for ions or for electrons, depending on the details of the space charge distribution as mentioned in this paper, which is important in focused ion beam applications where large aperture angles are needed to obtain high beam currents used for milling or deposition.
Abstract: We have investigated the use of space charge for the correction of spherical aberration in focused ion beam systems. A negative space charge cloud can be formed to reduce the spherical aberration of a lens for ions or for electrons, depending on the details of the space charge distribution. Spherical aberration is important in focused ion beam applications where large aperture angles are needed to obtain high beam currents used for milling or deposition, because it results in large tails on the current density distribution. A space charge distribution (cloud) can be produced with a small electron gun inside an electrostatic lens that can reduce this problem. We report on the properties of one such design.
6 citations
TL;DR: The phase spectrum-based method proposed by Koster et al. as mentioned in this paper has been demonstrated by a computerized 200 kV transmission electron microscope with a slow-scan CCD camera system, which has theoretical advantages compared to other methods utilizing diffractograms.
Patent•
04 Nov 1997
TL;DR: In this paper, the authors proposed a method to evaluate the focusing performance of an a focal optical system in a suitable measuring direction by eliminating the skill of the measurement, improving the operability and measuring the worst direction of an image.
Abstract: PROBLEM TO BE SOLVED: To evaluate the focusing performance of an a focal optical system in a suitable measuring direction by eliminating the skill of the measurement, improving the operability and measuring the worst direction of an image. SOLUTION: Pinholes P1 to P5 corresponding to the positions of a plurality of image heights of a lens 17 to be detected are formed at a pinhole plate 16, and uniformly illuminated from an entire light source 15. The plate 16 is moved in an optical axis direction at an X stage 21. Pinhole images (image surface 18 via the lens 17 is detected by CCD area sensors 41, and contrast transfer function MTF is calculated by Fourier transformation by a signal processing system 20. The system 20 detects the peak positions from the output signals of the pinhole images detected by the sensors 41 to 45, and calculates the peak positions by the Fourier transformed MTF based on the output section of the tangential T direction and radial R direction for passing the peak positions. It also calculates the MTF by the transformation based on the output section of the maximum deviating direction of the images detected by sensors 41 to 45, and evaluates the focusing performance of an afocal optical system at the image height.
01 Jan 1997
TL;DR: In this article, it was shown that the image formation process in a field-emission gun (FEG) electron microscope is the same as in a conventional transmission electron microscope, and that the spherical aberration coefficient of an FEG electron microscope may be measured by using an amorphous thin film.
Abstract: It is shown that for a weak phase object the image formation process in a field-emission gun (FEG) electron microscope is the same as in a conventional transmission electron microscope, and that the spherical aberration coefficient of an FEG electron microscope may be measured by using an amorphous thin film. Methods were developed for accurate determination of the spherical aberration coefficient of an FEG electron microscope using digital electron micrographs.