Showing papers on "Contrast transfer function published in 1989"

Contrast in the electron spectroscopic imaging mode of a TEM. I. Influence of zero‐loss filtering on scattering contrast

Abstract: SUMMARY Measured values of the transmission of amorphous films as a function of the objective aperture and film thickness can be described by a single-scattering theory for unfiltered and zero-loss filtered images in the electron spectroscopic imaging mode of a transmission electron microscope. The theory can be applied to estimate the gain of contrast by zero-loss filtering for specimen structures larger and smaller than the chromatic aberration disc.

Annular dark field electron microscope images with better than 2 Å resolution at 100 kV

Abstract: High‐resolution scanning transmission electron microscope (STEM) images in the annular dark field (ADF) imaging mode approaching the theoretical point‐to‐point resolution limit are presented. The ADF images were obtained from a high Tc superconducting YBa2Cu3O7−x thin‐film specimen at 100 kV. The 1.9 A resolution lattice image, which is the smallest lattice spacing in the specimen, corresponds to the minimum resolvable spatial frequency with 5% contrast in the contrast transfer function for annular dark field, and is smaller than the resolution limit given by the Rayleigh criterion. This demonstrates that STEM ADF imaging can have a resolution approximately 40% better than that of the bright field conventional transmission electron microscope (CTEM) imaging at Scherzer condition.

Three-Dimensional Microscopy: Image Processing For High Resolution Subcellular Imaging

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.

Image restoration in coherent imaging system involving spherical aberration

Abstract: This paper describes an image restoration method based on defocus modulation processing, assuming weakly scattered objects in the coherent imaging system involving spherical aberration. The present analysis shows that the effect of the spherical aberration can be completely corrected by the image integration applied to the defocus series, if appropriate bipolar (positive and negative) weighting functions as a function of the defocus value are used in the image integration

Some Aspects Of Quantitative X-Ray Microscopy

Abstract: A simple model of image formation in the x-ray microscope is used to investigate the relationship between contrast, signal to noise ratio, dose and image resolution. The important feature of this model is the role that the depth of field is expected to play in determining the dose to the specimen when imaging at high resolution, with the result that the dose can be expected to increase as the inverse sixth power of the resolution. Some deficiencies in this model are examined for the case of thin specimens, where linear contrast transfer theory can be applied, and it is shown that there are some advantages associated with the use of phase contrast imaging conditions. Finally, methods of producing phase contrast in the imaging microscope and the scanning microscope are compared in terms of their contrast transfer functions and the ease with which they can be realised in practice.

Spherical Aberration In Confocal Microscopy

Abstract: Scanning confocal microscopy has become an important tool in the field of optical sectioning and 3D-reconstruction of biological objects. Usually these samples are embedded in dispersive media, introducing depth dependent spherical aberration. Depth and lateral resolution are therefore impaired. We discuss this problem theoretically and show experimental results.

Electrostatic lens potentials with small relativistic spherical aberration

Abstract: We discuss a computerized systematic investigation to find axially symmetric electrostatic lens potentials with acceptable first‐order properties and small spherical aberrations. The calculation of the spherical aberration is based on the direct solution of the relativistic trajectory equation in paraxial and nonparaxial approximation. The potentials are characterized by their properties in infinite magnification mode. Conditions for the computations and constraints to satisfy practical requirements are prescribed. A successful axial potential distribution and its relativistic spherical aberration coefficient, the spherical disk radius, and some first‐order optical parameters, are also presented in the paper as an example.

3-Dimensional Microscopy Using Tilted Views

Abstract: The resolution of an optical microscope is considerably less in the direction of the optical axis (z) than in the x-y plane, typically by a factor of 5 or more. This is true of conventional or confocal microscopes. In order to alleviate this problem we have used multiple tilted views to supply the 'missing data' and thus increase the resolution in z. A special tilting microscope stage has been constructed, which allows specimens mounted on thin glass capillary tubes to be rotated through large angles. Through-focal data sets can then be collected from several mutually tilted viewing directions. The relative orientation, translation and z-sampling parameters for the data sets can then be determined by use of a novel phase/wiener cross-correlation function. Finally, the data sets, once brought to a common coordinate system, can be combined using amplitude and phase combination techniques in Fourier space borrowed from X-ray crystallography. We have applied this technique to metaphase chromosomes in intact embryos of Drosophila melanogaster. Images were collected using a liquid nitrogen cooled CCD array camera, and processed using a VAX computer. As judged from the maximum extent of significant power in the Fourier transform, the resolution of the final reconstruction was about 0.25,urn in x and y and better than 0.4,um in z. Although we have shown an application to data collected from a conventional fluorescence microscope, the technique is equally applicable to any other imaging mode or to confocal images.