A
Abbe condenser see condenser, Abbe.
German mathematician and physicist, professor at Jean, and inventor of much optical apparatus at the Zeiss works. His inventions include the apochromatic objective, the compensating ocular, the Abbe condenser, a well corrected oil-immersion achromatic condenser, the immersion objective, Abbe apertometer, Abbe refractometer, and the drawing camera; he evolved the Abbe theory of resolution and microscope imagery, the numerical aperture formula, and other optical theories.
In microscopy, a device for measuring simultaneously, the numerical and angular apertures of an objective or condenser. The back focal plane of the objective is viewed within auxiliary lens, and the device is set to show the position of an indicator just cutting into two opposite edges of the conoscopic field of view.
For a periodic structure of units separated by distance d and obliquely illuminated by the unrefracted ray and one of the two diffracted rays (extremely oblique illumination), Abby applied the law of diffraction: d = 0.5 lambda /NA, where: lambda = wavelength of the monochromic light or shortest of mixed wavelengths NA = the limiting numerical aperture (NA) (q.v.) of objective or condenser.
Abbe theory of image formation see Abbe theory of image formation
Ernst Abbe's specification for the limit of resolution of a diffraction-limited micro-scope. According to Abbe, a detail with a particular spacing in the specimen is resolved when the NA of the objective lens is large enough to capture the first-order diffraction pattern produced by the detail at the wavelength employed. See also Rayleigh criterion, Sparrow limit.
Includes a rack and pinion for horizontal displacement of an iris diaphram to obtain oblique lighting.
A long, wedge-shaped coverslip about 0.20 mm thick at one end and 0.10 to 0.12 mm at the other end coated chemically with a silver film on which are ruled horizontal lines. At each variation in thickness of 0.01 mm there are vertical lines. By means of oblique illumination and by focusing on different portions of the plate, it is possible to determine the optimum coverslip thickness for any objective and also, for microscopes with drawtubes, the tube length for best objective performance. The approximate freedom from spherical and chromatic aberrations can also be estimated. Small isolated bits of silver near the edges of the lines form good objects for the star test
Abbe's theory is based on the fact that a non-self-luminous particle, which is illuminated by an extraneous source, gives rise to diffracted light rays, in addition to the dioptric pencil. He stated that to form a good microscopical image as many of the diffracted rays as possible should be intercepted by the objective. With closely ruled lines, his theory is easily demonstrated by observing the back lens of the objective, for here the diffracted rays can be observed directly if the aperture diaphram is closed. It can be shown that, when the illumination is arranged to exclude the diffracted images, resolution is lost.
any error that results in image degradation. Such errors may be chromatic, spherical, astigmatic chromatic, distortion, or curvature of field: and can result from design or execution, or both.
aberration
Failure of an optical or electron-optical lens to produce exact geometrical (and chromatic) correspondence between an object and its image. In a video camera tube or cathode-ray tube, aberrations anse when the (electrostatic or electromagnetic) lens does not bring the electron beam to sharply focused points uniformly on the target or screen, or to correct geometrical positions, as the beam is deflected.
aberration
In an optical system, any defect that degrades its performance from that which could be achieved with a perfect lens, e.g., failure of an object point to be imaged as a point.
A defect in a lens or optical system due to the greater refraction of shorter wavelengths over that of loner ones at a lens surface. Hence the focal length of a simple lens is shorter for blue than for red rays. This dispersion of the wave-lengths will cause color fringes in the image field of a lens with such an aberration.
A lens defect whereby image forming rays of one color, passing through the outer zones of a lens come to focus at a different distance from the lens than do those of more central rays. With a simple spherical (or plano-spherical) lens the outer rays always meet the axis closer to the lens than do more central rays and the lens is uncorrected or "undercorrected". When the reverse is true the lens has been "overcorrected".
Extremely hard materials (Diamond, SiC, Al2O3.etc.), usually in a very fine particulate form (<15 micrometers), used in the initial stages of specimen preparation to grind and polish samples to the desired thickness or finish.
The act of adjusting the eye, to bring objects that are closer to the eye in focus. Contraction of the ciliary muscles relaxes the tension on the crystalline lens, which rounds up by virtue of its elasticity while also moving forward slightly. The net effect is to rescue the overall focal length of the eye.
literally, color-free. A lens or prism is said to be achromatic when corrected for two colors. The remaining color seen in an image formed by such a lens is said to be secondary chromatic aberration.
achromatic
Literally, color free. A truly achromatic lens would transmit light without decomposing it spectrally and there would be no color fringing in the image. A doublet, composed of a positive and negative lens element, can be made achromatic for two colors which much improves the performance for most of the others.
A well-corrected microscope condenser lens; corrected for chromatic and spherical aberrations and satisfying the sine condition.
also achromatic A lens cluster whose foci and power are made the same for two wavelengths (commonly for the red hydrogen C line, A = 6563 A, and blue F line, A =4861 A). The simplest achromatic is a doublet that combines two single lenses with different dispersions and curvatures to achromatize the combination. Even the simplest "achromatic 'microscope objectives contain two such doublets.
an objective that is corrected chromatic for two colors, and spherically for one, usually in the yellow-green part of the spectrum.
An intermediate, enclosed chamber of a vacuum or pressure system through which an object may be passed without effectively changing the vacuum or pressure of the main body of the system. Reference here is to the vacuum of all electron microscopes.
the image of a bright point object as focused by a lens system. With monochromatic light, it consists of a central point of maximum intensity surrounded by alternate circles of light and darkness caused by the reinforcement and interference of diffracted rays. The light areas are called maxima and the dark areas minima. The distribution of light from the center to the outer areas of the figure was investigated mathematically by Sir George Airy. The diffraction disk forms a basis for determining the resolving power of an ideal lens system. The diameter of the disk depends largely on the aperture of the lens. The diffraction of light causing the Airy disk is a factor limiting the resolution of a well corrected optical system.
airy disk
The bright disk of light (surrounded by alternating dark and bright diffraction rings)that is formed by a perfect diffraction-limited lens, focusing an image of an infinitely small source of light. For a minute absorbing spot, the diffraction pattern is a dark Airy disk surrounded by brighter and darker diffraction rings. Since the Airy disk is the smallest unit that makes up the image of a luminous or absorbing object (formed by a properly corrected microscope lens in focus), the radius of the disk determines the limit of resolution of the microscope.
A pattern of image sampling error in digital systems. Aliasing forces spatial frequency components higher than a critical value (the Nyquist frequency) to be displayed at progressively lower frequencies. Aliasing introduces an undesirable moiré pattern when the spatial frequency of the signal exceeds the sampling rate in a digitizer.
When the projected image of the microscope is projected less than 250 mm the objective may be moved enough from its usual position (for visual observation) to degrade the image. It can be restored by adding a lens above the ocular to bring the image into focus on the desired plane but with the objective still in its position of best-corrected image. A similar system requires an "ocular" in which the same corrections are made. Such lens systems are termed "amplifiers" (e.g., Homalsof Zeiss, Amphiplans of B & L, etc.).
an optical device, capable of producing plane polarized light, used for detecting the state of polarization.
analyzer
A second polarizing element inserted beyond a preparation. When its vibration direction is at right angles to the vibration direction of the polarize, the field becomes black if no anisotropic specimen is on the stage or when viewing an anisotropic substance in an extinction position or directly down an optic axis of an anisotropic crystal.
A metric unit of length measurement=
· 1x10 -10 meters or 0.0000000001 meters
· 4x10 -9 inches or 0.000000004 inches
· Atomic diameters range between 1 and 2 Angstroms
a unit of linear measure named after A. J. Ångström. It is 1 x 10 -10 metres: 1 um = 10.000 Å. It is generally abbreviated as A. in the United States: elsewhere, it is variously abbreviated A, A., A.U., Å., or ÅU.
angular aperture see aperture, angular
Quality of a transparent material having different refractive indices depending on the vibration direction of the transmitted light, hence any material that affects polarized light differently according to its direction through the material.
The difference in physical properties such as velocity of wave propagation, elasticity, refractive index, absorbance, etc., for the same material measured along different directions
The result of placing a stop in the first focal plane of the condenser to produce an illuminating cone of light with all the light flux near the surface of the cone. The central part of the cone will be dark. This arrangement is often used for a darkfield effect in low-power work by transmitted light. The condenser must be correctly focused and centered. By reflected light, darkfield illumination is attained with an annular con-denser fitted around the objective for opaque objects. Annular illumination implies that the object is lighted from all sides.
The opaque ring-shaped stop with a small central opening usually placed in the objective back focal plane to provide dispersion staining.
The electrode to which a major flow of electrons takes place internally (as in a cathode-ray tube) or to which an external positive voltage supply is connected.
A thin (<100 micrometer thick) disk or strip of metal (usually Pt) with a small (2-100 micrometers) circular through-hole. Used to restrict electron beams and filter out unwanted scattered electrons before image formation.
aperture
In optics an aperture is an opening that restricts the size of the light beam that enters or leaves a lens or lens system and is often controlled by an iris aperture diaphram. Its correct placement can be a very critical matter. The aperture can, of course, be filled by a lens; it can be at a focal plane of the lens as is that of the substage condenser of a microscope. Opening this aperture wider increases image brightness and definition(resolving power) but decreases depth of field and contrast. Aperture size is measured variously according to the field of use of the lens, often by its simple diameter as is that of the telescope. The free aperture of a lens is that which is unrestricted except by its own diameter.
In a video camera tube or monitor, the aperture refers to the size and shape of the electron beam that lands on the target or phosphor. In an optical instrument, the opening of a lens or aperture stop.
anode aperture: The opening in the accelerating voltage anode shield of the electron gun through which the electrons must pass to irradiate the specimen. condenser aperture: An opening in the condenser lens controlling the number of electrons entering the lens and the angular aperture of the electron beam. The angular aperture can also be controlled by the condenser lens current. physical objective aperture: A metallic diaphram, with a small central hole, used to limit the cone of electrons accepted by the objective lens. This improves image-contrast since highly scattered electrons are prevented from arriving at the Gaussian image plane and therefore cannot contribute to background fog. aplanatic. Free from spherical aberration and coma.
An electronic process used in some high-resolution video cameras and monitors that compensates for the loss in sharpness of detail due to the finite dimensions (aperture) of the scanning beam.
In a diffraction-limited optical system, the function that determines the relationship between the image and each point in the object. Modifying the aperture function changes the image according to the modified Fourier-filtering (or optical filtration) property of the aperture.
In a microscope adjusted for Koehler illumination, the conjugate planes that include the light source, the condenser iris diaphram, the objective lens back aperture, and the eye point. Spaces in the aperture planes are the reciprocal of those in the field planes.
aperture, angular
the angle between the most divergent rays that can pass through a lens to form the image of an object.
The angle subtended between the axis of a lens and the largest accepted angle of the image-forming rays. With microscope objectives the trigonometric sine of this angle is used to define numerical aperture (NA)(q.v.) but as measured from the axial object point. (Note: Some commercial advertising literature has erroneously used the full angle in defining NA.)
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Produced by an incident electron colliding with the nucleus of an atom in the specimen. The incident electron is then scattered "backward" about 180 degrees with no appreciable loss of energy, an elastic collision.
The production of backscattered electrons from a sample varies directly with the specimen's average atomic number; higher atomic number elements produce more backscattered electrons than lower atomic number ones. Detection of Backscattered Electrons is achieved by using a "donut" shaped solid state semiconductor device mounted on the bottom of the objective lens. When Backscattered Electrons strike the detector electron-hole pairs are created which are then counted. This quantity is translated into a pixel intensity and displayed on the CRT, forming the image. By splitting the detector into halves (or quadrants) differences in the signal level on the individual detector segments provide surface topography information.
The exit pupil of a microscope objective lens. The objective lens back aperture, which can be examined with a phase telescope or by inserting a Bertrand lens, displays the conoscopic interference figure and diffraction patterns.
As measured on the principal axis, from the second lens vertex to the back focal point of the lens. It is not the equivalent of the focal length.
The plane, normal to the lens axis, situated at the back focus of a lens.
In any compound lens (a lens system composed of more than one lens element), the last lens through which the light passes is called the back lens. It may be a single simple lens, a doublet, or triplet.
a resin from the balsam fir Abies balsamea. Dissolved in xylene, toluene, or benzene it is used as a mountant for permanent microscopical preparations. Its refractive index may vary from 1.530 to l.545 and its softening point from room temperature to 100deg.C, these properties varying with age and solvent content. If impure it discolors with age.
A distortion, or aberration,
The microscope's supporting structure such as the horseshoe type. Heavier bases, some containing the entire illuminating system, began to appear after World War II.
When the liquid phase of a microscopical mount has arefractive index different from that of the solid phase, a line or narrow band of light can be observed around or just within the outlines of the specimen as the microscope tube is raised or lowered from its position of best focus. The presence of the line indicates the difference in index referred to, and its absence, there-fore, indicates similarity of index between the specimen and its mounting fluid. The Becke line is useful in determining the refractive index of transparent, microscopic particles.
The distance from the eye point to the image plane in a photomicrographic apparatus.
A small, low-power lens, usually on a slide for insertion into the drawtube between analyzer and ocular. It is used to observe the back focal plane of the objective so as to examine interference figures or as an aid in achieving interference figures. It is apt to be strongly astigmatic. It is used to image the lamp filament in setting up Kohler illumination as well as for centering dispersion staining stops to the substage aperture diaphram.
Anisotropic crystals in the orthorhombic, monoclinic and triclinic systems. They have three principal refractive indices alpha, beta, and gamma, and two isotropic directions, i.e., optic axes. bifilar eyepiece. An ocular with two crossed hairs, wires, filaments or threads each of which has perpendicular motion.
A microscope fitted with double eyepieces for vision with both eyes. The purpose in dividing the same image from a single objective of the usual compound micro-scope is to reduce eyestrain and muscular fatigue which may result from monocular, high-power microscopy. The purpose in obtaining a different image for each of two oculars is to provide stereoscopy by means of two different angles of view. There are two kinds of stereoscopic microscopes: binobjective (Greenough) older type and monobjective (common main objective, CMO) newer type.
The numerical difference in refractive indices for a substance. In a given crystal view, the interference color (retardation) between crossed polars depends on the birefringence and thickness: Retardation (nm) = 1000 x thickness (m) x birefringence
in biaxial crystals, that principal axis of the ellipsoid of indexes which bisects the smaller angle between the optic axes.
in biaxial crystals, that principal axis of the ellipsoid of indexes which bisects the larger angle between the optic axes.
An imaging mode in a TEM that uses only unscattered Electrons to form the image. Contrast in such an image is due entirely to mass-thickness variations in amorphous samples, and may include diffraction contrast in crystalline samples.
The method of lighting the specimen with a solid cone of rays. Transmitted bright field illumination is performed by a substage condenser. Reflected bright field illumination is performed by a vertical illuminator.
The brightness of an extended luminous source is termed the intensity per unit area measured in candles per cm 2. Also, the intensity of reflection; it may be measured in lamberts; one lambert equals 1 lumen/cm 2.
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- a doubly refracting mineral used in the manufacture of polarizing prisms. It is uniaxial negative and in the trigonal diversion of the hexagonal system of crystals. Its indexes are epsilon =1.486, omega =1.658; its hardness is 3 on the Mohr scale and specific gravity 2.711.
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- A condenser designed with two reflecting surfaces; the first, a spherical surface which reflects the rays to a second, cardioid (heart-shaped) surface. The virtue in such an arrangement is that, if the cardioid surface is of true figure, the lens is both achromatic and aplanatic. It has a limiting numerical aperture of about 1.0. Thus objectives of a greater numerical aperture cannot be used successfully with it. A "true" cardioid figure is the trace of a point on the circumference of a circle rolling around an equal, fixed circle.
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- Named after Cassegrain, astronomer of the 17th century. A high-power, dark field con-denser to be used with objective apertures as high as 1.3. It is sometimes called the luminous spot ring condenser (Zeiss).
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- An optical system in which both reflecting and refracting curved surfaces are used to form an image. Some ''reflecting" objective lenses, as well as video projection systems, are catadioptric; the latter uses a Schmidt plate to correct the spherical aberration introduced by the spherical reflecting mirror.
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- An opaque disk placed in the ring carrier or diaphragm carrier of the substage apparatus. It excludes the central rays and is used for dark field work at low magnification. Variable stops can be contracted or expanded as desired.
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- An X-ray having a unique energy that is emitted by an atom in the sample during its de-energization after ionization of one of its electrons by an incident electron.
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- a defect in a lens or lens system as a result of which the lens possesses different focal lengths for radiation of different wavelengths.
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- A lens used to produce a collimated beam from a light source. With a true point source on the axis the beam would be an axial tube of parallel rays With practical sources having real area the beam will be a diverging cone of parallel rays from each light point; this beam still has special properties and can be collected again by a good lens.
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- the operation of controlling a beam of radiation so that if the light source were a point, the light rays would become parallel. The total bundle of rays diverge as the source size increases.
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- A suspension of sub-light-microscopic particles. This definition arbitrarily limits the size of the particles to 0.1 - 0.005mm. Such particles may be studied by dark field illumination, particularly with the light ultramicroscope or by means of an electron microscope.
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- a lens aberration occurring in that part of the image field that is some distance from the principal axis of the system. It results from different magnification in the various lens zones. Extra-axial object points appear as short comet-like images with the brighter small head toward the center of the field (positive coma) or away from the center (negative coma).
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- A lens aberration in which the off-axis beams do not form single focused spots but rather comet-shaped patterns .
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- A lens aberration which occurs in part of the image field which is slightly away from the principal axis of the system. It results from different magnifications in the various lens zones. It causes extra-axial object points to appear as short comet-like images, with the tail either toward the center of the field (positive coma) or away from the center (negative coma). Coma is fundamentally due to faulty position of the principal points of the lens.
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- those designed for use with objectives such as apochromats in order to correct chromatic aberration .
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- a term applied to lenses or mirrors designed to collect, control, and concentrate radiation in an illumination system.
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ABBE CONDENSER
- originally a two-lens substage condenser combination designed by Ernst Abbe. It lacks chromatic correction though designed for a minimum of spherical aberration and has only a very low-angle aplanatic cone. It may be rated with a numerical aperture as high as 1.3.
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- The image of the aperture iris diaphragm of the substage condenser as seen in the back focal plane of the objective.
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- In microscopy, the lens mounted before the microscope stage, which transmits light to the object. There are two main categories of condensers: (1) bright field and (2) dark field. Bright field condensers are of four distinct types: (a) Abbe condenser, an uncorrected condenser composed of two separable lenses; (b) aplanatic condenser; (c) achromatic condenser which has full corrections for color and spherical aberrations; (d) aplanatic achromatic condenser. the dark field condenser for low powers may be nothing more than a low-power bright field condenser with a central stop. Medium- or high-powered dark field condensers are usually of the cardioid or paraboloid type. The lamp lens is loosely called a condenser lens, but light-collecting lens is a more definite term. All microscope condensers must be carefully focused and aligned for best results.
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- a condenser forming a hollow cone of light with its apex (or focal point) in the plane of the specimen. When used with an objective having a numerical aperture lower than the minimum numerical aperture of the hollow cone, only light deviated by the specimen enters the objective. Objects are seen as bright images against a dark background.
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- The ordinary bright field condenser of low power, used with a central stop, makes a good dark field condenser. See special dark field condensers: paraboloid, cardioid and Cassegrainian. They all form a dark field while illuminating the specimen with a hollow cone of light. The lower limiting aperture of the condenser must be greater than the NA of the objective with which it is to be used. Thus, no direct light enters the objective; the specimen is seen by reflected or scattered light on a dark background.
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- a dark field condenser consisting of a convex spherical reflector mounted concentric with a larger concave reflector. The rays are formed into a diverging cone by the convex reflector. The annular concave reflector then forms a hollow converging cone which is focused on the subject. See
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- a dark field condenser consisting of a reflecting surface in the form of a segment of a paraboloid of revolution. Parallel rays entering the condenser around the periphery of the central stop are reflected from the curved surfaces and converge at the focus of the paraboloid. See
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- essentially an Abbe condenser in which the upper lens element is fixed and the lower movable. The lower lens may be used to focus the illumination between the elements so that it emerges from the stationary lens as a large diameter parallel bundle. The field of low-power objectives may thus be filled without removing the top element. At the opposite extreme it can be adjusted to have a numerical aperture as high as 1.3. .
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- A (microscope) optical system in which the condenser and objective lenses both focus onto one single point in the specimen. Generally, the image of a pinhole source is focused onto a point in the specimen, and that point is focused by the objective lens onto a point detector or through a mask with a pinhole aperture. With confocal optics, the Abbe limit of resolution can be exceeded since only a limited region of the specimen is viewed at any onetime.
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- In an image-forming system, two fields are said to be conjugate with each other when two or more object fields are simultaneously in focus in a single plane, e.g., in Kohler illumination the field diaphragm, specimen and ocular front focal plane are conjugate foci as are the filament, condenser aperture diaphragm, objective back focal plane and ocular front focal plane(when a Bertrand lens is used).
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- Planes (or points) that are in focus relative to each other. In a microscope adjusted for Koehler illumination, there are two sets of conjugate planes: the aperture planes and the field planes.
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- The interference pattern and diffraction image seen at the back aperture of the objective lens. The conoscopic image provides a two-dimensional projection of the rays traveling in three dimensions in the specimen space.
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- The study of the back focal plane of the objective by removing the eyepiece, by inserting a Bertrand lens, by examining the image at the eye point above the eyepiece with a magnifier or by using a phase telescope is called conoscopic because the observations are associated with the cone of light furnished by the condenser and viewed by the objective (cf. orthoscopic).
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- A measure of the gradation in luminance that provides gray scale (or color) information. Contrast is expressed as the ratio (difference in luminance)/(average luminance) in adjoining areas of the scene. Under optimum conditions, the human eye can just detect the presence of 2% contrast.
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- A manual control on a monitor that affects both the luminance and contrast of the picture.
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- Also Square wave response curve.
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- A term applied to 'normal' TEM imaging. The electron beam is passed through a thin film sample (typically ~1-200 nm thick). Bright field diffraction contrast images are formed with the direct (undiffracted) beam. Dark field images are formed with a selected diffracted beam. CTEM imaging is used in the general observation of samples and careful selection of the diffracting conditions of the sample will allow the analysis of defect structures within the sample.
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- In color video cameras and monitors, the precise alignment of the images or pictures in the three primary colors (red, green and blue). A lack of convergence gives rise to asymmetrically colored fringes.
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- An electron probe is tightly focused on a TEM specimen and the resulting pattern of diffracted electrons is observed. The patterns contains information on the crystal symmetry and atomic and electronic structure of the sample. Regions as small as 0.2 nm may be examined.
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- The comparatively hard covering on the outside of the front part of the eyeball.
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- An adjustment collar provided on some high-NA, microscope objective lenses. Rotation of the collar adjusts the height of certain lens elements in the objective lens to compensate for variations in coverslip thickness or immersion media. At high NAs, even a small deviation of the coverslip thickness (by as little as a few micrometers in some cases), or refractive index of the immersion medium from the designated standard, can introduce significant aberrations.
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- A screw adjustment, generally under constant spring tension, which affords a method for controlling under- or over-correction by altering the spacing of the two rear lens combinations in the specific 2 mm and 4 mm objectives. It makes possible the adaptation of the lens to various coverslip thicknesses, usually from 0.10 to 0.20 mm. The graduated collar is turned until the optimum image is obtained, as determined by the star test, (which employs a pin hole to act as a "star") or, more often , by critical examination of the image.
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- Thin glass, plastic, sapphire, SiO, NaCl, etc. shaped into circles, squares, or rectangles for covering the specimen. Glass coverslips, grade no. 1 1/2, contain a high proportion of covers from 0.17 to 0.18 mm in thickness, close to the lens designer's specifications for employment of achromatic and apochromatic objectives of high NA. The thickness and refractive index of the glass coverslip are important because certain of their values have been assumed by the designer and manufacturer. These values have been specified by ASTM: thickness, commercial number 1 1/2: 0.16 to 0.19 mm; refractive index measured at the sodium D lines (589.3 nm), 1.523(0.005).
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- a crystalline substance which is anisotropic with respect to the velocity of light.
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- The configuration in which atoms are arranged in a material. These arrangements have a direct effect on the physical properties of the material. These arrangements commonly take the form of cubes, rectangular solids, hexagonal solids.etc.
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- a property of lens that causes the image of a plane to be focused into a curved surface instead of a plane.
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- The image plane formed by a single lens is naturally curved. While one part of the field will be in good focus, the rest will need refocusing to be sharp. While the eye may partially correct for this, a camera lens will not, and the final image as photographed will not be in perfect focus over the entire image plane.
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- Any method of illumination which illuminates the specimen but does not admit light directly to the objective. It may be by substage condensers; by stagespot lighting, by special condensers fitted around special objectives for reflected illumination or by the slit ultramicroscope.
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- Using a single diffracted beam to form the image in a TEM. This causes all regions of the specimen not of the same crystal structure and orientation as the region which produced the diffracted beam to be represented as very dark in the final image; allowing phase differentiation visually in the TEM.
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- Certain objectives for high-power, dark fieldwork equipped with iris diaphragms or funnel stops so that their apertures may be reduced to correspond to the dark field con-denser with which they are used.
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- Owing to the exacting demands of dark field illumination, not only must the microscope slide be especially clean, but also the glass of which the slide is composed must be optically clear under dark field conditions. The glass should not fluoresce. For general use and for special work, see ASTM specifications.
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- A central stop for obtaining a dark field effect for low-power objectives. It is customarily used with a high NA, bright field condenser.
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- A fitting with a small iris diaphragm, attached above a low-power objective for reducing the aperture. In this way depth of field can be increased for the photomicrography of objects illuminated by incident light.
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- The distinctness with which the very fine detail in an image or photograph can be seen.
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- The degree of detail or sharpness in a video picture.
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- The electromagnetic coils that steer the electron beam in a cathode-ray tube or image pickup tube, e.g., in a raster scan
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- A term applied particularly to the rating of neutral filters and to the measurement of the density of negatives. Mathematically, it is the logarithm (base 10) of the reciprocal of the transmission.
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- logarithm to the base 10 of the reciprocal of transmittance.
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- the depth or thickness of the object space that is simultaneously in acceptable focus.
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- The distance between the closest and farthest objects in focus within a scene as viewed by a lens at a particular focus and with given settings. The depth of field varies with the focal length of the lens and its f-stop setting or NA; and the wavelength of light. Depth of fields only a small fraction of a micrometer can be achieved at 546 nm with microscope lenses of N.A. > 0.9.
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the depth or thickness of the image space that is simultaneously in acceptable focus.
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- The range of distances between a lens and image plane (target in the video pickup device) for which the image formed by the lens at a given setting is clearly focused. With a high-NA microscope objective, the depth of field is very shallow, but the depth of focus can be quite deep and reach several millimeters.
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- a fixed or adjustable aperture in an optical system. Diaphragms are used to intercept scattered light, to limit field angles, or to limit image-forming bundles or rays.
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- The deliberate outer limit to the size of a beam of light entering or leaving a lens or lens system. The diaphram used to restrict the effective size of a lens should lie in its principal plane or be imaged in it. In a lens system, such as a micro-scope with its lamp, an aperture diaphram is one that is imaged in the objective aperture and limits the angular extent of the illumination beam. The field diaphram is imaged in the microscope field of view and protects the image from "stray light". In a photographic lens the diaphram is sometimes called a "stop".
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- An optical phenomenon in which a crystalline structure exhibits two different colors depending on the direction of observation or the plane of vibration of polarized light waves, traveling through the crystal. It is a form of pleochroism (exhibiting many colors), which reflects the difference of absorption curves for chromophores oriented in different directions within the crystalline structure.
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- A mode of contrast generation in microscopy that yields an image with a shadow relief. The relief reflects the gradient of optical path difference. DIC, which is a form of interferenc microscopy that uses polarizing beam splitters, can be of the Smith or Nomarski type.
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- Periodic scattering of moving objects when they collide with an orderly pattern of fixed objects. Diffraction always follows Bragg's Law {n*Wavelength=2*Spacing of fixed objects*sin(angle of scattering)}. This periodic scattering is useful in determining the spacing of the fixed objects since all other variables in the equation are know. In Electron Microscopy the spacings being determined are those between atoms in a lattice or crystal.
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- When light passes an edge, because wave undulation is involved, it tends to curl around the edge, as would water waves. This small fraction is usually not observed as it is overwhelmed by the rest of the undeviated light. However, when two parallel edges are brought close together to form a slit, excluding most of the unaffected light, this spreading of the light according to wavelength becomes apparent; the shorter the wavelength the more it is bent--blue more than red. With many slits together, i.e. a grating, this is most evident and it can be used instead of a prism. When there are two parallel slits another phenomenon can be observed. Abbe showed that it is diffraction at the minute edges of the specimen that limits observable detail with the microscope. In this case the interference involved is with the undeviated beam of light diffraction disk.
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- An artificially produced periodic array of scattering centers capable of producing a pattern of diffracted energy, such as accurately ruled lines on a plane surface.
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- An optical unit representing the reciprocal of the focal length (in meters) of a lens, in terms of the meter. A 1 diopter lens has a focal length of 1 meter, a 2-diopter lens has a focal length of 1/2 meter, etc. The diopter expresses the power as in spectacles or other weak lenses.
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- An old term, relating to study of image formation by a lens due to refraction. It is not included in the general term, ego-metrical optics.
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- The variation of refractive index with color (or wave-length) of light. The spreading of white light into its component colors when passing through a glass prism is due to dispersion which, in turn, is due to the fact that the refractive index of transparent substances is lower for long wavelengths than for-short wavelengths. A measure of dispersion is defined as: nD - 1 v= nF-nC where nD = refractlve index at 589 nm (yellow); nF = 486 nm (blue); nC = 656 nm (red).
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- A procedure involving central or annular stops in the objective back focal plane to induce colored images of transparent particles mounted in liquids with indices matching the particle at a wavelength in the visible. The particle and liquid should possess very different dispersion curves for best colors.
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- When a simple lens is used as a magnifier for visual observation the eye becomes part of the optical system. A "virtual image" can be formulated by construction and its apparent distance will vary with the focus of the eye. This will vary among individuals. In a rather arbitrary but standardized assumption, the "normal distance" for close observation, or reading has been set at 10 inches (250 mm). Therefore, by agreement, the magnification of a simple magnifier: 10 (inches) 250 (mm)
m= focal length (inches) = f.l (mm) The optics for the compound microscope have been designed to furnish parallel light from the eyepiece so that the eyes are relaxed for distant viewing. This makes the virtual image lie at "infinity". Tests showed that the average observer accommodates somewhat, placing the virtual image rather variably, often about 20 - 25 feet.
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- The aberration of image distortion results when the magnification varies over the extent of the field. (1) barrel distortion. This distortion results when the magnification increases from the center toward the edges of the field. This is also called negative distortion. (2) pincushion distortion. This distortion is the result of decreasing magnification outward from the center of the field. It is also called positive distortion.
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- In signal processing, the lack of correspondence of the wave forms in the output relative to the incoming signal caused by undesired nonlinear processing. The amplitudes or phases of certain frequency components have changed relative to other frequency components. In imaging, geometrical distortion refers to the lack of correspondence of the shape (proportional distances) of the image relative to the image produced by an idealized lens or device. Geometrical distortions are expressed as a percentage of distances departing from the distances in a non-distorted image.
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- The refraction of light in two slightly different directions to form two rays or vector components. Each ray is polarized, and their vibration directions are perpendicular to each other. Furthermore, each ray has a different velocity, and therefore a different refractive index.
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- Two simple lens elements cemented together, for the purpose of giving spherical and chromatic corrections. An achromatic doublet may be composed of a positive crown-glass lens and a negative flint-glass lens. The errors of one element are made to compensate those of the other element.
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- The smaller of the two tubes on a monocular microscope. The drawtube (if present) carries the ocular; it can be adjusted to control tube length and so effect corrections for the objective lens. The drawtube may also be convenient in calibrating an eyepiece-micrometer by allowing a minor magnification change to simplify the conversion factor.
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- any microscope objective designed for use without immersion liquids.
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- An automatic focusing adjustment of the electron beam in high-quality cathode-ray or video image pickup tubes. The beam is made to land with the properly shaped minimum-sized spot regardless of its position in the raster scan
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- In video and other electronic equipment and in photographic emulsions, the ratio of the maximum to minimum signal levels that introduce no more than acceptable levels of signal amplitude distortions.
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- an electromagnet designed to produce a suitably shaped magnetic field for the focusing and detection of electrons or other charged panicles in electron-optical instrumentation.
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- An electromagnet designed to produce a suitably shaped magnetic field for the focusing and deflection of electrons or other charged particles in electron optical instruments
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- Propagated forms of energy with electrical and magnetic fields and with wavelengths from gamma-rays through x-rays, ultraviolet, visible, infrared to radio waves.
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- A sub-atomic particle which allows the atom to react with its environment and form bonds with other atoms. Electrons and their orbits around the nucleus of an atom account for most of the physical properties of the element. Used extensively in Electron Microscopy.
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- A stream of electrons in an electron optical system.
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- A pattern formed by the periodic backscattering of electrons by the specimen lattice in a SEM. Allows determination of crystal structure and lattice parameters in crystals >10 micrometers diameter.
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- The phenomenon, or technique of producing diffraction patterns through the incidence of electrons upon matter.
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- Electron energy loss spectroscopy analyses the inelastically scattered electrons present in the beam after it has been transmitted through the sample. An EEL spectrum typically consists of a monatomic decreasing background on which are superimposed a number of peaks. Each peak is characteristic of the scattering process that has occurred in the sample. The peaks can be used to obtain information about the chemical composition and electronic structure of the sample. EEL spectra are acquired typically in a magnetic sector spectrometer located under the camera chamber of the TEM. Spatial resolution is typically limited by the minimum probe diameter of the microscope. EELS tends to be complimentary to EDS in that it can be used to analyze very thin samples of low Z materials.
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- A cathode/anode device intended to produce a stream of electrons.
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- A device for producing and accelerating a beam of electrons.
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- The assembly inside a video camera tube and monitor picture tube that contains a heated cathode. Electrons emitted by the gun are focused to produce the scanning beam.
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- A representation of an object formed by a beam of electrons focused by an electron optical system.
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- A device for focusing an electron beam.
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- A photographic reproduction of an image formed by the action of an electron beam.
electron microscope
- microscope, electron see microscope, electron
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- The study of materials by means of an electron microscope.
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- The path of an electron through an electron optical system along which it suffers no deflection due to lens fields. This axis does not necessarily coincide with the mechanical axis of the system.
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- A combination of parts capable of producing and controlling a beam of electrons to produce an image of an object.
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- the science that deals with propagation electrons, as light optics deals with that of light and its phenomena.
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- The science that deals with the propagation of electrons, as light optics deal with that of light and its phenomena.
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- A narrow beam of electrons used to scan or illuminate an object or screen.
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- The qualitative and quantitative use of x-rays excited by a microprobe of electrons.
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- The path of an electron.
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- The rate of motion of an electron.
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- The wavelength necessary to account for the deviation of electron rays in crystals by wave diffraction theory. It is numerically equal to the quotient of Planck's constant divided by the electron momentum, mv. = h / mv; where: h = Planck's constant m = mass of electron v = velocity of electron
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- A lens employing a permanent magnet to produce a potential field capable of deflecting electron rays to form an image of an object. (cf. electromagnetic lens).
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- EDS is a microanalytical technique that is based on the characteristic X-ray peaks that are generated when the high energy beam of the electron microscope interacts with the specimen. Each element yields a characteristic spectral fingerprint that may be used to identify the presence of that element within the sample. The relative intensities of the spectral peaks may be used to determine the relative concentrations of each element in the specimen. The X-ray signal is detected by a solid-state silicon-lithium detector and the construction and efficiency of this detector sets a lower limit on the atomic number that may be detected. Generally elements heavier than carbon (Z=5) are detectable.
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- The apparent size of the limiting aperture of a lens or lens system (properly that of the diaphram), as seen from the object plane. This can shift and become a complex matter in some circumstances. In a properly set up microscope system it should be that of the substage iris diaphram.
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- Scanning electron microscopy is performed by scanning a focused probe across the surface of the sample to be studied. In the environmental SEM the composition and pressure of the atmosphere around the specimen may be controlled. In favorable cases non-conductive specimens may be examined without coating, and hydrated specimens may be examined with the water still in place.
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- The focal length of the simple lens that has the same power as the compound lens. The stated focal lengths of microscope objectives are the e.f. since their front and back focal lengths are very different.
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- The exit pupil of a lens system is an image of the entrance pupil (hence conjugate to it) and normally should be the image of the limiting diaphram. In both the microscope and the telescope it is the eyepoint where the beam has its smallest cross-section. It is also called the Ramsden circle or eyepoint.
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- While using a polariscope, such as a polarized light microscope, extinction of the light image occurs when a birefringent object (such as a crystal or fiber) is turned between crossed polars to such a position that its illumination on the dark field has been extinguished. Usually extinction of the birefringent object occurs at 90 degrees rotation intervals of the stage, (which is perpendicular to the axis of the microscope or other polariscope).
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- In a polarizing or DIC microscope, the ratio of the amount of light that is transmitted with the axes of the polars parallel over the amount transmitted with their axes crossed. Unless the lenses are rectified, the EF drops exponentially as the NA is increased.
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- Vibration directions oblique to the long direction of the crystal or fiber.
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- Vibration directions parallel and perpendicular to the long direction of the crystal or fiber.
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- Vibration directions bisecting a prominent crystal profile angle.
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- The angle between the nearer vibration direction and a prominent direction of the crystal. It never exceeds 45 degrees
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- The lens nearest the eye in any ocular.
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- the lens system used in an optical instrument for magnification of the image formed by the objective.
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- An ocular in which the real image of the object is formed between two lenses.
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- eyepieces with common focal planes so that they are interchangeable without refocusing.
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- an eyepiece in which the real image of the object is formed below the lower lens element, of the eyepiece.
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- An ocular in which the real image of the object is formed below the lower lens of the eyepiece.
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- A measure of the relative aperture of a lens; its light gathering capacity. It is equal to the ratio of the focal length of the lens divided by the diameter of its limiting opening (aperture): f-number = focal length/iris diameter. Note that the number becomes smaller as the aperture grows larger and that it must be squared to directly measure the area which is the light gathering capacity.
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- A second bright line which moves in the direction opposite to the Becke line. It is usually observed with thick particles or when the refractive index difference between particles and mountant is large. It appears as a concentration of reflected light at the high index side of the interface.
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- For the normal eye, the far point is at infinity. The rays of light from an infinitely distant point source are parallel and can be focused with the accommodation muscles of the eye entirely relaxed.
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- The fast ray or fast component for a crystal or fiber corresponds to the lower refractive index.
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- The area of the object that is seen when the image is observed. It may range in diameter from several millimeters to less than 0.1 mm. The magnification and the size of the diaphram opening in the eyepiece governs the diameter of the field of view.
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- The thickness of the object space within which objects f
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