Seiler Precision Microscopes > Resources

View our FAQs or find a dental or medical manual to help with your questions. If you cannot find what you need, contact us and we will find what you need!

Questions?
Need more information
about your Seiler product?

View our FAQs or find a dental or medical manual to help with your questions. If you cannot find what you need, contact us and we will find what you need!

Definitions

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

ABERRATION	An optical defect which is inherent in the design of a lens. The failure of a lens to bring all the rays of light to an exact focus.
ACHROMATIC LENS (without color)	A lens consisting of two or more elements, usually made of crown glass and flint glass. This lens has been corrected for chromatic aberration in it has the same focal length with respect to two selected colors (red and blue) or wavelengths of light. The resultant image is free of extraneous. It is also corrected for spherical aberration with respect to one color.
ALIGNMENT	See collimation
AMPLIPLAN EYEPIECE	See eyepiece
ANALYZER (polarizing)	See polarized light
ANASTIGMAT	A compound lens corrected for astigmatism.
ANGLE OF INCIDENCE	The angular measure between an incoming light ray striking the surface and the normal (a line perpendicular to the surface) at this point. This is the angle theta, in sketch below) symbol theta = angular distance.
ANGLE OF REFLECTION	The angular measure between a reflected light ray and the normal to the reflecting surface. For any surfaces the angle of incidence equals the angle of reflection.
ANGLE OF REFRACTION	The angular measure between a refracted ray (one that has been "bent" at the bounding surface) ant the normal to this surface.
ANGSTROM	A unit of length of light waves used in spectroscopy. See units of measurement, also wavelength.
ANNULAR APERTURE (annulus)	see phase annulus.
APERTURE (diaphragm, stop, pinhole, slit)	A fixed or variable opening or hole through which light may pass.
APLANATIC LENS	A compound lens simultaneously corrected for the aberrations of coma and spherical aberration.
APOCHROMATIC LENS	An improved achromatic lens. While the acromatic lens corrects for the colors of red and blue only, the apochromatic lens corrects for three colors (red, blue and green), greatly reducing the fuzziness caused by the colors uncorrected in the acromat. In addition, the lens is better corrected for spherical aberration, and generally has a higher numerical aperature than the acromat.
ASTIGMATISM	The lens aberration in which horizontal and vertical lines are focused at two different points along the optical axis. The image is clearest somewhere between these two points.
AVERAGE FOCUS	The best focus taken as a compromise over the whole field of view.

BALCOTED LENS	A Bausch and Lomb lens which has been given an anti-reflection treatment. The thin, tough coating applied to the lens surface helps produce a sharper, clearer image by reducing external and internal reflections and increases contrast.
BIREFRINGENCE	The term applied to materials which reflect light in a manner that depends on its state of polarization. These materials have more than one refractive index. Examples are crystals (excluding cubic), and some biological specimens.
BODYTUBE	The part of the microscope that contains the eyepiece and the objective lenses.

CALIBRATE	To determine the correct scale intervals for any measuring device or to ascertain the errors of the scale, such as the focusing scale of a camera lens.
CENTRATION	The accuracy with which the optical axis of the lens coincides with the mechanical axis of the mounting.
CHROMATIC ABERRATION	The optical defect of a lens which causes different colors or wavelengths of light to be focused at different distances from the lens. It is seen as color fringes or halos along edges and around every point in the image.
CHROMATIC DIFFERENCE OF MAGNIFICATION	See lateral color
CIRCLE OF LEAST CONFUSION	The best point of focus for an image. It is the smallest cross section of a focused light beam.
COLLIMATION	The alignment of two lens systems so that when properly adjusted the optical axes of the two systems are pointed in the same direction. Accuracy of alignment and freedom from double image increases efficiency and comfort for the user. For example, binocular lens system.
COLORIMETER	A direct reading instrument incorporating a precision grating for the analysis of solutions by photometric comparison,. The result is a percent transmission or optical density, and the concentration of the unknown is obtained from a working curve or table prepared from standard solutions of the material under examination.
COMA	An aberration due to the non-convergence of rays originating from points not on the optical axis. The image a point appears not as a tiny circle, but as a pear-shaped figure lacking good definition.
COMPENSATING EYEPIECE	see eyepiece
CONCAVE (negative) LENS	see lens
CONDENSOR	A simple or compound lens used to "gather" light rays and focus them on the object to be illuminated. Some types of microscope condensers are: Abbe- The simplest form of substage condenser of good light gathering ability, but it is not corrected for spherical or chromatic aberration. Achromatic condenser- corrected for both spherical aberration and chromatic abberation. It is the most nearly perfect type for bight field work since its optical qualities approach those of the objective. Dark field condenser- does not admit light to the microscope, but illuminates the object so that it appears luminous against a background of little or no light. There are several types of dark field condensers. Phase contrast condenser- Transmits light through annular rings so as to work in conjunction with a phase altering pattern in the objective. See phase contrast. Variable focus condenser- changes the numerical aperature of illumination with a single condenser by means of movable elements. (The numerical aperature of an Abbe or achromatic condenser is changed by manually removing one or more elements from the condenser itself.)
CONTRAST	The degree of difference in tone, brightness, or color from point to point or from highlight to shadow is an object or image. Contrast is degraded and whole image is hazed or grayed down when reflections from surface to surface in a lens system come out as "flare", "scatter light", or "ghost images".
CONVEX (positive) LENS	see lens
CORRECTED LENS	A lens or lens system which corrects for aberrations; remedies deviations of light rays from object to eye, to produce a clear, sharp image.
CORRECTION	The elimination or reductions of the several aberrations which appear in the image from ant lens or lens system. The reduction or balancing out by optical design of distortion, curvature of field, and chromatic aberration results in an image that is sharp and clear.
CRITICAL ANGLE	The maximum angle of incidence that can be formed by a light ray in passing from a dense medium to a less dense medium. The angle is measured between a ray and a perpendicular erected at the intersection of the ray with the surface of the medium. The critical angle of an air-glass surface is about 42 degrees. Use of this fact is made in totally reflecting prisms in which the light strikes the prism wall at an angle of 45 degrees and is reflected instead of passing through the bounding surface. The critical angle is the basic principle employed in the refractometer.
CRITICAL ILLUMINATION	see illumination
CROWN GLASS	Optical glass having a low dispersion and usually a low index of refraction. Compare with flint glass. See refractive index for sketch.
CURVATURE OF FIELD	An aberration in which the surface of best focus is not a plane, but a curved surface. (The edges of the field appear to be out of focus when the central portion is focused clearly.)
CURVATURE OF LENS	The amount of sharpness of curve in a lens surface.

DARKGROUND ILLUMINATION	a lighting technique for showing detail in transparent objects. Only light which has reflected off of the object is allowed into the objective lens. This method produces a view of bright objects on a dark background.
DENSITOMETER	An instrument designed to measure the optical density of an optical element, system or material.
DEPTH OF FIELD	The distance along the optical axis throughout which the object can be located and yet be imaged with satisfactory clarity.
DEPTH OF FOCUS	The distance along the optical axis throughout which the image formed formed by a lens is focused clearly.
DEVIATION	the angular difference between the original path of a light ray and its path after passing through one or more optical boundaries.
DIFFRACTION	The small scale sidewise spreading of light waves after going past the edge of an obstacle or passing through a small aperature. It is this effect which makes the edge of a shadow appear blurred and causes the halos around images of bright spots of light.
DISPERSION	the separation of "complex" light (light composed of a mixture of colors) into its component colors.
DISTORTION	The aberration of a lens which causes the image to appear misshapen and deformed due to a gradual increase or decrease in magnification from the center to the edge of an image. The images of straight lines, therefore, appear curved.
DOUBLET	A pair of lenses cemented or mounted together to form a single lens system for the purpose of correcting chromatic abberation, and also monchromatic aberrations.

ECHELLE	A form of grating usually having relatively few lines per square inch. Used at a high angle and crossed with another dispersing member (as in the Echelle Spectrograph), it provides higher dispersion, higher resolution and wider spectral range, but in a moderately sized instrument. To obtain these same results with a conventional grating spectrograph design would require an instrument of impractical size.
EMPTY MAGNIFICATION	High magnification which increases the size, but does not increase the detail, due to the limitation of the resolving power.
ENTRANCE PUPIL	A limiting stop behind the optical system. it is the circular edge of a disc of light that can be seen by looking through the front end of the lens at some distance from the eye.
EQUIVALENT FOCAL LENGTH	In a compound lens having several simple lenses with a common optical axis, this is the focal length of the system considered as a whole.
EXIT PUPIL	A limiting stop behind the optical system. It is the circular edge of a disc of light that can be seen by looking through the back end of the lens at some distance from the eye.
EYEPIECE (sometimes called ocular)	In a compound microscope, the complex magnifying lens group nearest the eye through which the observer views the enlarged real image formed by the objective lens. ampliplan eyepiece- designed for only microprojection and photomicrography to produce flatness of field. compensating eyepiece- primarily corrected for use only with apochromatic objectives, eliminating the color fringes found when ordinary eyepieces are used with such objectives. Huygenian eyepiece- this simple eyepiece effects a certain amount of correction for chromatic difference of magnification in the achromat objective hyperplane eyepiece- has a larger field and a flatter image than the Huygenian eyepiece, and a color compensation midway between that of the Huygenian and that of the compensating eyepiece. Ramsden eyepiece- similar to the Huygenian but has its focal plane either on or just outside surface of collective lens. Used for measuring applications where good image quality of scale is desired. ultraplane eyepiece- designed for microprojection and photomicrography to compensate to the fullest extent possible for curvature of field and lateral color. wide field eyepiece- has a large field of view and a high eyepoint. It is used with low magnifying powers to examine large sections of the specimen simultaneously.
EYEPIECE GRATICULE	a piece of clear film or glass with lines marked on it which fit into a microscope's eyepiece. It is often used with a stage micrometer to measure an object.
EYEPOINT	The proper location of the eye when using a visual instrument. Note that the converging cones of light are the smallest at the eyepoint.
EYE RELIEF	The distance from the eye lens of the microscope or other instrument to the eyepoint.

F/NUMBER	The ratio of the focal length of a lens to its effective aperture. A measure of the "speed" of a lens or its ability to gather light.
FIELD OF VIEW	The open or visible space commanded by a lens. In a compound microscope, it is the area that is visible when the instrument is in focus.
FILTER	A transparent material characterized by selective absorption of light according to wavelength.
FLATNESS OF FIELD	Appearance of the image to be flat; a plane in the object is imaged as a plane. See curvature of field.
FLINT GLASS	A heavy, brilliant optical glass having a high dispersion and usually a high index of refraction. Compare with crown glass.
FLUORITE (semi-apochromatic) OBJECTIVE	An objective which combines with glass the crystal, Fluorite, which because of its dissimilar index of refraction and dispersion produces an image quality approaching that of apochromatic objectives. Better resolving power than the achromatic, but moderate in cost compared to the apochromatic.
FOCAL LENGTH	The distance from a point where the image of a distant object is formed (focal point) to a point in or near the lens.
FOCAL PLANE	The plane at right angles to the optical axis at the focal point. This plane contains the image of a distant object if the lens is free of field curvature.
FOCAL POINT (Principal focus)	That point where the light rays coming from a distant object converge after passing through a lens, coming to a focus and forming an image. If the light rays start from such a point, these rays become parallel to each other after passing through the lens.
FOCUS	The point at which light rays through a lens intersect to form an image.

GRATING

An optical unit for producing spectra by diffraction. Close equidistant and parallel grooves are ruled on a polished surface, commonly a glass base, coated with a film of aluminum. Can be reflection or transmission type. Surface can be plane or convex. Number of grooves varies from several hundred to many thousand per inch according to dispersion required.

ILLUMINATION	In many types of microscopes a ground glass filter is placed over the illuminator to give even diffused light; but where a more concentrated light beam is desired, as in critical visual or photomicrographic work, two kinds of illumination may be used. critical illumination- that form of illumination in which the light source is imaged directly on the specimen, giving a narrow, intense light beam Koehler illumination- includes field diaphragm control. This type is generally preferred because the iris diaphragm of the illuminating unit directly controls the field of view, and uneven distribution of energy in the source does not result in uneven brightness in field of view. In dark field microscopy, a special illuminator is designed for use with a paraboloid condensor and is attached to it. In dark field work without an attached illuminator, an intense light source such as a carbon arc lamp is recommended.
ILLUMINATOR	In a microscope, the source of light which illuminates the specimen to be viewed.
IMAGE DISTANCE	The distance along the optical axis from the optical center of the lens to the point where the image is formed.
IMAGE PLANE	The plane at right angles to the optical axis at the image point. See focus.
INDEX OF REFRACTION	see refractive index
INFRA-RED	That portion of the spectrum where the wave lengths are too long for the human eye to see. These colors can be recorded, however, due to recent improvements in photographic techniques.
INTERFERENCE	The effect produced by the interaction of two light waves on the total intensity of light. Constructive interference increases intensity, while destructive interference diminishes it, at times producing total darkness if interacting light waves meet certain conditions. Interference fringes are alternate bright and dark bands caused by light waves merging from two adjacent openings and "interfering" with each other.
INTERFERENCE FILTER (transmission type)	Two highly reflecting but partially transmitting films of silver separated by a spacer film of non-absorbing material. This combination is deposited on a glass plate by high vacuum methods and protected by a cemented cover plate. The separation of the silver films governs the wavelength position of the pass band and hence the color of the light which the filter will transmit. The principle of optical interference is used to accomplish selective or colored transmission.
INTERFEROMETER	A precision measuring device using the interference of light waves. The units of measure involved are usually millimicrons.
IRIS DIAPHRAGM	An opaque disc with an opening which can be expanded or contracted, like the iris of the eye. This produces a large range of openings to meet different conditions.

KOEHLER ILLUMINATION

see Illumination

LATERAL COLOR (chromatic difference of magnification)	An abberation in which light of one color is imaged at a greater magnification than light of another color. This causes an off-axis image of a point object to be spread out into a tiny spectrum or spread of color.
LENS	A transparent object (made of optical glass, fluorite, or quartz, etc.) having two polished surfaces of which at least one is curved, usually with a spherical curvature. It is shaped so that the rays of light passing through is are made to converge or to diverge. Two common types of lenses are convex (positive) lenses, converging lenses with a bulging appearance, and concave (negative) lenses, diverging lenses with a curved-in appearance. Lenses are of many shapes depending upon the purposes for which they are designed.
LENS SYSTEM	Two or more lenses arranged to work in conjunction with one another in order to accomplish a required job. For example, a condensor system, a projection lens system, a microscope, etc.
LIGHT	An electromagnetic radiation capable of inducing visual sensation through the eye. It travels in a vacuum at a constant speed of 186,000 miles per second. This speed is less when the light travels through some material substance such as glass or water.

MACROSCOPE	An instrument for viewing gross objects at low magnification. Image is right side up and unreversed.
MAGNIFICATION	An enlargement of an object by an optical element or instrument. It is the ratio of the size of the image to the actual size of the object under observation.
MAGNIFYING POWER (expressed as "times" or "X" or "power"	A measure of the ability of a lens or combination of lenses to make an object appear larger. It is the number of times the image seen through the instrument is larger than the object appears to the unaided eye.
MENISCUS	A crescent shaped lens - one which is concave on one surface, convex on the other. It may be either converging or diverging.
METALLOGRAPH	An instrument for recording photographically images seen in a metallurgical microscope.
METALLURGICAL MICROSCOPE	see microscope
MICROMETER DISC	A ruled transparent plate placed in the eyepiece of a microscope to make possible accurate measurements of an object being studied.
MICRO-PROJECTOR	An instrument for projecting microscopic images onto a screen. Microprojection is intended solely as a supplement to, rather than a substitute for visual microscopy.
MICROSCOPE	A high precision optical instrument which uses light to study objects. It is capable of high magnification and is used for making minute details visible. bright field microscope- the type most ordinarily used in laboratory work. Stained slides are usually used. dark field microscope- makes the specimen appear luminous against a background of little or no light. Used for objects displaying feeble contrast in a bright background. dark field microscope- makes the specimen appear luminous against a background of little or no light. Used for objects displaying feeble contrast in a bright background. phase contrast microscope- used for viewing living specimens or other low contrast specimens which would ordinarily not be visible in the bright field microscope. This microscope uses the principles of diffraction also refraction and scattering. Interference is also a factor to show up the slight differences in optical path. polarizing microscope- employs polarized light to show changes in internal structure and composition of material no discernible with ordinary light. Used extensively in industry for product control. See polarized light. stereoscopic wide field upright microscope- used to give a three dimensional view of a large specimen. Has a limited magnification range (to about 200x).
MONOCHROMATIC LIGHT	Light of one color (wave length).
MONOCHROMATOR	A form of spectrometer which emits light of a single wavelength from any portion of the spectrum in the source.

NOSEPIECE	The part of an optical microscope where the objective lenses are attached.
NUMERICAL APERTURE (N.A.)	A term representative of the angle included by a cone of light emitted by the condensor and accepted by the objective of a microscope.

OBJECT DISTANCE	The distance from the optical center of a lens along the optical axis to the point where the object to be viewed is located.
OBJECTIVE	The function of the objective is to produce a real, enlarged and inverted image of the object.
OBJECTIVE LENS	The compound lens system in a microscope or other optical system which receives light from the field of view and forms the first image. This is the lens on an optical microscope which first magnifies the object. Aberrations must be corrected to a high degree in this lens, since any optical defects present are accentuated when the image is magnified by the eyepiece.
OPTICAL AXIS OF A LENS	Line joining centers of curvature of the two spherical faces of the lens.
OPTICAL BENCH	An instrument for ascertaining the physical properties and aberrations of a lens or lens system.
OPTICAL CENTER	The point in a lens through which, if light rays pass, they will suffer no angular deviation.
OPTICAL ELEMENT	A unit lens, prism, mirror or other optical part of an optical system. It is usually made of a single piece of material.
OPTICAL GLASS	Glass carefully manufactured to obtain a controlled index of refraction and dispersion, purity, transparency, homogeneity and workability. The two most common types of optical glass are the crowns and the flints.
OPTICAL PATH	That branch of physical science which is concerned with the nature and properties of light

PHASE ANNULUS	A transparent ring on an opaque background used in a microscope condensor to limit the illumination to a hollow conical beam of light, for use as a phase contrast illuminator.
PHASE CONTRAST	A special method of controlled illumination, for observing thin transparent objects whose structural details vary only slightly in thickness and refractive index and, therefore, are not visible in the bright field microscope. This method involves interference of a portion of the light with the rest in such a manner as to produce a visible image.
PHOTOMACROGRAPHY	The photographic recording of images of gross specimens at low magnification. The microscope is replaced by photomacro lenses mounted on the front board of the camera
PHOTOMICROGRAPHY	The photographic recording of images seen in a microscope
PLANO	Pertaining to flat; a plano lens has no curve. A plano-concave lens has one flat surface and the other curved inward. A plano-convex, one flat the other curved outward.
POLARIZED LIGHT	Light which is vibrating in one plane only. Normal emitted light (a mixture of light waves vibrating in all directions) may be polarized by reflection, double refraction, selective absorption, or scattering. Polarization enables distinguishing the changes in structure and the composition of material that are not discernable with ordinary light. Change in appearance under polarized light serves as identification.
POLARIZING MICROSCOPE	see microscope and polarized light
PRINCIPAL FOCUS (the focal point)	The focal point for a beam of light rays parallel to the optical axis of a lens or spherical mirror.
PRISM	A transparent body (made of optical glass, fluorite, or quartz, etc.) with at least two polished plane faces inclined toward each other from which light is reflected or through which light is refracted.
PROJECTION DISTANCE	The distance from the projection lens to the screen upon which the image is in focus; commonly termed "throw".

REAL IMAGE	An image which the eye can see and which can be displayed on a screen (the opposite of virtual image).
REDUCTION	The process of making a small image from a large object
REFLECTION	The return of light from an optical surface into the same medium from which it came.
REFRACTION	The change in direction of a ray of light that occurs when it falls obliquely upon a surface separating two media through which light travels at different velocities.
REFRACTIVE INDEX	The ratio of the speed of light in air to its speed in another medium. This ratio determines the amount of bending of light rays. The higher the index, the more bending of light.
REFRACTOMETER	An instrument for identifying or grading substances by means of their characteristic refractive index, dispersion, or percentage dissolved solids.
RELATIVE APERTURE	The ratio of the diameter of a spherical mirror or lens to its focal length. If a lens surface includes a relatively large fraction of the entire spherical surface of which the lens surface is a part, the lens surface is said to be of large aperture. If it includes only a relatively small portion, the aperture is small.
RESOLVING POWER (resolution)	A measure of the ability of a lens to image closely spaced objects so that they are recognized as separate objects. Chromatic- The ability of a spectrographic instrument to distinguish slightly differing wavelengths.

SCANNING ELECTION MICROSCOPE	The Scanning Electron Microscope (SEM) provides three-dimensional pictures of the surface topography of a specimen. This is accomplished by scanning the specimen with a fine electron beam synchronized with the beam of a cathode ray picture tube. This imaging of three-dimensional objects is due to the fact that SEM does not record the electrons passing through the specimen, but the secondary electrons released from the sample by the electron beam impinging on it. The SEM depth of field is 500 times that of an optical microscope.
SPECTROGRAPH	An instrument for producing and photographing a specimen from which measurements can be made. It permits analysis of materials that produce spectra in the ultraviolet, visible, and infrared regions.
SPECTROMETER	An instrument designed to break up light from a source into its constituent wavelengths and to indicate wavelengths on its calibrated scale.
SPECTROPHOTOMETER (spectrum light measurer)	An instrument for measuring the amount of light for each component wavelength in the spectrum of a sample being analyzed.
SPECTROSCOPE	An optical instrument used for visual observation of the visible portion of a spectrum.
SPECTRUM	An orderly dispersed system of radiant energy derived from atomic or molecular vibration and arranged by wavelength expressed in millimicrons (m mu) or Angstrom Units (A). Of the entire spectrum the portions most commonly used are ultra-violet (1,850 to 4,000A); visible (4,000 to 7,000A); and infrared (8,000 - 35,000A).
SPEED (of a lens)	see f/number and numerical aperture.
SPHERICAL ABERRATION	An optical defect in which the lens fails to form a sharp image due to characteristics of the curved lens surfaces where the rays are refracted. Rays of light which pass through a lens near its edge are converged to a point nearer the lens than those rays passing through near the center. Spherical aberration may be reduced by a proper choice of radii of curvature of the lens surfaces or by stopping down the lens (inserting a diaphragm in the beam so as to expose only the central portion of the lens.)
STAGE	The part of the microscope where object to be viewed is placed. There is a hole in the middle to let light shine through to illuminate the object from below.
STAGE MICROMETER	A piece of clear film or glass slide which has a measurement scale marked on it. It is placed on stage of microscope to measure the size of an object.
STEREOSCOPIC VISION	That particular application of binocular vision which enables the observer to view an object for two different perspectives of an object such as two photographs taken from different camera stations) to obtain the mental impression of a three dimensional object. The stereomicroscope employs binocular vision.
STOP	A diaphragm in the path of a light beam inserted so as to expose only the central portion of the lens. A stop controls either the quantity of light transmitted or the field of view.

TRIPLET

Three lenses cemented or mounted together as a single lens system to achieve aberration correction.

ULTRA-VIOLET

That portion of the spectrum where the wavelengths are too short for the human eye to see. Ultra-violet light is used in photomicrography with special optics (usually quartz). Using these short wavelengths for obtaining the photograph results in an increase of two or three times the normal resolving power.

VIRTUAL IMAGE

The eye can "see" a virtual image, but the image itself will not appear when a screen is placed at the spot where the image is perceived to be.

WAVELENGTH

Light travels in waves varying in length. Measurement is from top of one wave to top of next one and is usually measured in units of millimicrons (mu) or Angstroms (A).