ABERRATION (Optical)

An optical aberration defect is inherent in the design of a lens and is the failure of a lens to bring all the rays of light to an exact focus.

ACHROMATIC LENS (without colour)

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 that it has the same focal length with respect to two selected colours (red and blue) or wavelengths of light. The resultant image is free of extraneous colour. It is corrected for spherical aberration with respect to one colour.

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 q as, in sketch below) symbol q = 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. (This is the angle q, in sketch below) symbol q = angle distance

ANGLE OF REFRACTION

The angular measure between a refracted ray (one that has been "bent" at the bounding surface) and the normal to this surface. (This is the angle q, in sketch) symbol q = angular distance.

ANGSTROM

A unit of length of light waves used in spectroscopy. See Units of Measure", also "Wavelength"

APERTURE

The aperture is a fixed or variable opening or hole through which light may pass. Opening the aperture wider increases image brightness and definition (resolving power) but decreases depth of field and contrast.

APERTURE DIAPHRAGM

A diaphragm that limits the rays into a lens system.

APLANATIC LENS

A compound lens simultaneously corrected for the aberrations of coma and spherical aberration.

APOCHROMATIC LENS

An improved achromatic lens that corrects the colours of red and blue only, the panchromatic lens corrects for three colours (red, blue and green), greatly reducing the fuzziness caused by the colours uncorrected in the achromatic. In addition the lens is better corrected for spherical aberration, and generally ahs a higher numerical aperture than the achromatic.

ARTICULATING ARM

A type of stand that holds a microscope body. The stand clamps to a table and has a variety of motion in three dimensions.

ASTIGMATISM

Astigmatism is a defect in the lens in which horizontal and vertical lines are focussed 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.

BARREL FOCUS

The body tube of the microscope moves to focus the objective lenses and the stage is fixed.

BASE

The bottom support of the microscope.

BINOCULAR

Having two eyepieces. All stereoscopes and some microscopes are binocular. Since each individual is different, binocular scopes allow for inter papillary adjustment (eye spacing).

BIREFRINGENCE

The term applied to materials which refract light in a manner that depends on its state of polarization. These materials have more than one refractive index. Examples : crystals (excluding cubic), and some biological specimens.

BODY TUBE LENGTH

The distance between the objective and the top of the body tube, usually 160mm. Obejectives are designed for a specific length, if mis-matched , spherical aberration will occur.

BRIGHT FIELD ILLUMINATION

A method of lighting the specimen with a solid cone of rays. Transmitted, bright field illumination is preferred by a sub-stage condenser. Reflected bright field illumination is performed by a vertical illuminator.

C-MOUNT

This is an adapter used with various types of video cameras. Usually, you unscrew the lens from the camera and screw in the adapter. The adapter then connects to the trinocular port on the microscope.

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

An optical defect of a lens which causes different colours or wave lengths of light to be focussed at different distances from the lens. It is seen as colour fringes or halos along edges and around every point in the image.

COARSE FOCUS

A focusing system that has both the coarse and fine fousing knobs mounted on the same axis. Usually the coarse knob is larger and on the outside and the fine knob is smaller and on the inside. On some coaxial systems, the fine adjustment is calibrated, allowing differential measurements to be recorded.

COAXIAL

Focusing system where the coarse and fine focus are mounted together on a common axis.

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 effect due to the non-convergence of rays originating from points not on the optical axis. The image of a point appears not as a tiny circle, but as a pear-shaped figure lacking good definition.

COMPENSATING EYEPIECES

Eyepieces designed for use with objectives such as apochromats in order to correct chromatic aberration.

CONDENSER

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 sub-stage condenser of good light gathering ability, but it is not corrected for spherical or chromatic aberration.

Achromatic Condenser - Does not admit direct 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 aperture of illumination with a single condenser by means of movable elements. (The numerical aperture 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 in an object or image. Contrast is degraded and whole image is hazed or grayed down when reflections from surface to surface in lens system come out as "flare", "scatter light", or "ghost images".

CONTRAST PLATE

A circular opaque plate placed on the stage of a low power microscope. One side is white, the other is black. It can be flipped around depending on the coloration of your specimen.

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 reduction of the several aberrations which appear in the image from any 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.

COVER SLIP

A very thin square piece of glass or plastic placed over the specimen on a microscopic slide. When used with liquid samples, it flattens out the liquid and assists with single plane focusing.

CRITICAL ANGLE

The smallest angle that will completely reflect a ray within a fiber.

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 focussed clearly)

CURVATURE OF LENS

The amount of sharpness of curve in a lens surface.

DARK FIELD ILLUMINATION

Any method of illumination which illuminates the specimen but does not admit light directly to the objective.

DARK FIELD OBJECTIVE

Certain objectives for high-power, dark field work equipped with iris diaphragms or funnel stops so that their apertures may be reduced to correspond to the dark field condenser with which they are used.

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 by a lens is focussed clearly.

DEVIATION

The angular difference between the original path of a light ray and its path after passing through one or more optical boundaries.(In the figure, q is the angle of deviation.)

DIAPHRAGM

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.

DIFFRACTION

The small scale sidewise spreading of light waves after going past the edge of an obstacle or passing through a small aperture. It is this effect which makes the edge of a shadow appear blurred and causes the halos around images of small bright spots of light.

DIN OPTICS

A German standard for the manufacturing of microscope lenses. DIN lenses aren't particularly better than non-DIN but they will be interchangeable from one DIN microscope to another. All of our microscopes except the entry level instruments use DIN optics.

DISPERSION

The seperation of "complex" light (light composed of a mixture of colours) into its component colours.

DISTORTION

The aberration of a lens which causes the image to appear misshapened 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.

DIVERGING LENS

Also known as divergent lens, negative lens, concave lens or dispersive lens. A lens that causes parallel light rays to spread out. The lens surfaces may be plano-concave, doule convave or concavo-convex. The edge of a diverging lens is always thicker than the center.

DOUBLET

A pair of lenses cemented or mounted together to form a single lens system for the purpose of correcting chromatic aberration and also monochromatic aberrations

ECHELLE

A form of grating usually having relatively few lines per inch. Used, at a high angle and crossed with another dispersing member (as in the Echelle Spectograph), it provides higher disersion, higher resolution and wider spectral range, but in a moderately sized instrument. To obtain these same results with a conventional grating spectograph design would require an instrument of impractical size.

EFFECTIVE APERTURE

The maximum diameter of a pencil of rays in object space emitted from an axial object point at an infinite distance and passes through an optical system.

ELECTRON MICROSCOPE (Transmission)

An optical instrument that uses electrons to illuminate the specimen for viewing. It is generally used to view items too small to be seen through an optical microscope. In the transmission electron microscope, a very this slice (500A or less) of a specimen is continually illuminated by a collimated beam of electrons that are scattered in passing through the sample. An especially-shaped magnetic field focuses this scattering, and provides an image of the specimen on a fluorescent screen.

EMPTY MAGNIFICATION

High magnification which increases the size, but does not increase the detail, due to the limitation of the resolving power.

ENTRANCE PUPIL

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, a limiting stop behind the optical system.

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.

ERECTING SYSTEM

An optical system that inverts an image vertically and horizontally.

ERECTING IMAGE

An image whose lateral magnification is a positive value both vertically and horizonally.

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.

EYE LENS

The lens of an eyepiece nearest the observer's eye.

EYEGUARD

A shield of rubber, plastic or metal used to protect the eyes of the observer from stray light and wind, and to maintain the proper eye distance.

EYEPIECE (sometimes called ocular)

In a compound microscope, the complex magnifiying 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.

Compensationg eyepiece- primarily corrected for use only with apochromatic objectives, elimination the colour 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 achromatic 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 Hygenian but has its focal plane either on or just outside surface of collective lens. Used for measuring applications where good image quality of the 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.

EYEPOINT

The proper location of the eye when using a visual instrument.

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.

FIBER BUNDLE

A rigid or flexible, concentrated assembly of glass or plastic fibers used to transmit optical images or light.

FIBER OPTICS

The branch of optical technology concerned with the transmission of radiant power through fibers made of transparent materials such as glass, fused silica or plastic.

FIELD STOP

An opening that limits the field of view of an optical instrument.

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.

FINE FOCUS

The knob used to fine tune the focus on the specimen. It is also used to focus on various parts of the specimen. Generally one uses the coarse focus first to get close then moves to the fine focus knob for fine tuning.

FIXED ARM

A type of stand used with low power microscopes. The arm and body are integral parts of the microscope and connected solidly to the base. See post stand and universal stand.

FLARE

A phenomenon of light spreading on an image surface, caused by multiple internal reflections in an optical system.

FLATNESS OF FIELD

Appearance of the image to be flat; a plane in the object is imaged as a plane. See curvature o field.

FLINT GLASS

A heavy, brilliant optical glass having a high dispersion and usually a high index of refraction. Compare with crown glass. See refractive index for sketch.

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 o 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 it he 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. See principal focus for sketch.

FOCUS

The point at which light rays through a lens intersect to form an image.

GHOST

Undesirable images formed on the image surface of an optical system that appear off the regular image location (duplicate images).

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.

GREENOUGH MICROSCOPE

One of two kinds of stereomicroscopes with two separate compound microscopes, one for each eye, focused on the same object.

HEAD

The upper part of the microscope that contains the eyepiece tube and prisms. On some microscopes the head is easily removable and replaceable. A monocular haead has one eyepiece, a binocular has two (one for each eye), a dual head has two but they are not together, and a trinocular head has three, one which is generally used for a camera connection.

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 the paraboloid condenser 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

A representation of an object produced by means of radiation usually with a lens or mirror system.

IMAGE DISTANCE

The distance along the optical axis from the optical center of the lens to the point where the image is formed. See focus for sketch.

IMAGE PLANE

The plane at right angles to the optical axis at the image point. See focus.

INFRA-RED

That portion of the spectrum where the wave lengths are too long for the human eye to see.

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 the 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 colour of the light which the filter will transmit. The principle of optical interference is used to accomplish selective or coloured transmission.

INTERFEROMETER

A precision measuring device using the interference of light wave. 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.

LATERAL COLOUR (chromatic difference of magnification)

An aberration in which light of one colour is imaged at a greater magnification than light of another colour. This causes an off-axis image of a point object to be spread out into a tiny spectrum or spread of colour.

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 on passing through it 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.

LENS SYSTEM

Two or more lenses arranged to work in conjuction with one another in order to accomplish a required job. For example, a condenser 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 unversed.

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.

MECHANICAL STAGE

A device provided for adjusting the position of a specimen, usually by translation in two directions at right angles to each other.

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 photographical images seen in a metallurgical microscope.
MICROMETER (micron)

One millionth of a meter represented by um. A micro is equal to 10 to the minus 6 meters.

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 precisin 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 field microscope.

Metallurgical Microscope - designed for visual examination, with magnification of opaque objects, polished metal specimens, and similar materials.

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 polarizing light to show changes in internal structure and composition of material not 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)

MIRROR

Allows you to direct ambient light up through the hole in the stage and illuminate the specimen.

MONOCHROMATIC LIGHT

Light of one colour (wave length)

MONOCHROMATOR

A form of spectrometer which emits light of a single wavelength from any portion of the spectrum in the source.

NANOMETER

A nanometer is one billionth of a meter. A nanometer is equal to 10 to the minus 9 of a meter.

NUMERICAL APERTURE (N.A.)

The sine of the vertex angle of the largest cone of meridional rays that can enter or leave an optical system or element, multiplied by the refractive index of the medium in which the vertex of the cone is located. Generally measured with respect to an object or image point, and will vary as that point is moved.

OBJECT

The figure seen through or imaged by an optical system. It may contain structures, natural or artificial, or it may be the real or virtual image of an object formed by another optical system. In optics, an object should be considered as an aggregation of points.

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. See focus for sketch.

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. 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.

OIL IMMERSION

A lens that requires a drop of special oil on the subject for use. The oil is put on the cover slip, and the objective is actually lowered into the oil. Oil immersion lenses are sealed so as to not be damaged by the oil.

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 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. See crown glass and flint glass.

OPTICAL PATH

Refractive index of medium times its thickness or length.

OPTICS

That branch of physical science which is concerned with the nature and properties of light.

PARCENTERED

A microscope that is parcentered is one in which the object in the center of view will remain in the center when the objective is rotated.

PARFOCAL

A microscope that is parfocal is one which, if it is in focus with one objective, wh4en the object is rotated, will remain in focus.

PHASE

The position of a wave in its oscillation cycle.

PHASE ANNULAS

A transparent ring on an opaque background used in a microscope condenser 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

PLAN APOCHROMATIC OBJECTIVE LENS

A modern, high NA microscope objective lens designed with high degrees of corrections for various aberrations. It is corrected for spherical aberration in four wavelengths (dark blue, blue, green & red), for chromatic aberration in more than these four wavelengths, and for flatness of field. A single plan APO objective may contain as many as 11 lens elements.

PLANO

Pertaining to flat; a plano lens surface 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. See lens for figure.

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 tat are not discernable with ordinary light. Change in appearane under polarized light serves as identification.

POST STAND

A type of stand used with low power microscopes. It consists of a single post rising vertically from the base. The microscope body can rotate about the post and also be moved up and down on it.

POWER SUPPLY

Refers to the voltage and current necessary for the operation of circuit devices
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".

PROJECTION LENS

The final lens in the electron microscope. The lens focuses the electrons onto a fluorescent screen to produce the visible image.

RACK AND PINION

Term used to describe the gear system for lowering and raising the stage or barrel when focusing. The coarse adjustment control (knob),

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 ration determines the amount of bending of light rays. Note the stronger bending by the flint (high index) glass.

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.

RETICLE

An optical element located at an image plane, containing a pattern that assists in pointing an instrument or measuring target characteristics. It may be as simple as a pair of crossed lines or a complex pattern. In semiconductor pattern generation, a glass or quartz substrate bearing the image of an integrated circuit.

RESOLUTION LIMIT

The minimum distance between two points or lines that can be distinguished in an optical system

RESOLUTION POWER

The ability of an optical instrument such as a telescope, microscope, or human eye, to distinguish two separate points or lines close to each other.

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 distinquish slightly differing wavelengths.

RESOLUTION READING

A number indicating how many lines per millimetre are contained in the finest group that can be distinquished on a resolution chart. The resolution chart is a device used to test resolving power; usually alternate black and white lines of equal width arranged in groups of decreasing line width, identified as the number of line pairs per millimetre.

RING LIGHT

An independent light that usually connects to the microscope body and gives off a ring of light.

SCANNING ELECTRON 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 electronic beam synchronized with the beam of a cathode ray picture tube. This imaging of tree-dimensional pbjects is due to the fact that the 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. See Electron Microscope.

SLIDE

A flat glass or plastic rectangular plate that the specimen is placed on. It may have a depression or well to hold a few drops of liquid.

SPECIMEN

A piece or portion of a sample selected for examination. The specimen may, or may not be representative, whereas the sample may have been selected to be representative.

SPECTROGRAPH

An instrument for producing and photographing a spectrum 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 wavelength 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 (1850 to 4000A); visible (4000 to 7000A); and infrared (8000 - 35,000A).

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

A device used for holding a sample in position in the optical path.

STAGE MICROMETER

A graduated scale used as a standard on the stage of a light microscope for calibrating an eyepiece micrometer, also for determining the magnification of a set-up in photomicrography, etc.

STEREO MICROSCOPE

Wide-field, low-magnification device that consists of two compound microscopes focused on a single object, producing an erect three-dimensional image.

STEREOSCOPIC VISION

A microscope (simple or compound) for each eye (binocular), giving different aspects and , therefore, a stereoscopic effect. There are two kinds of compound stereomicroscopes: binobjective and common main objective (CMO). See Greenough Microscope.

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.

T- MOUNT

A type of adapter used to mate still cameras (usually 35mm) to microscopes.

TELECENTRIC SYSTEM

An optical system whose aperture stop is located at one of the foci of the objective lens so that the principal ray passes through the focal point.

TOTAL MAGNIFICATION

The final magnification of the microscope is the result of objective magnification x eyepiece magnification with consideration of the tube factor.

TRANSMITTED LIGHT

The usual method for illuminating transparent microscopic specimens. The light is concentrated on the specimen by the sub-stage condenser. Objects appear in outline (refraction images) or coloured on a bright field (colour images).

TRINOCULAR HEAD

Available on both high and low power microscopes, tri heads have two eyepiece lenses (one for each eye) and a thir port at the top for a camera. Some microscopes give you the option of sending all the light to the tri ort, or perhaps half and half, or maybe 70/30%. On some stereo tri heads with dual power, the tri port transmits the image through the set of lenses not being used by the stereo eyepieces.

TRIPLET

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

TUBE

The connection between objective and eyepiece. According to DIN the mechanical tube length is 160 mm.

TUBE FACTOR

Is given if its value is other than 1.0 and must be added to the eyepiece magnification. It is due to optical systems between objective and eyepiece or to a change in the tube length.

TURRET

With several objectives, a precision-engineered part of the microscope.

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.

UNIVERSAL STAND

A long boom type arm used to support a (low power) microscope body. It has many adjustments allowing the microscope to be aligned in a wide variety of configurations. Generally one uses an external (like a fiber optic) light source with a universal stand.

VIDEO MICROSCOPY

Microscopy that takes advantage of video as an imaging, image processing, analyzing or controlling device.

VIGNETTING

An unintentional, shaded loss of the edges of an image or picture by an optical component clipping the peripheral beams can lead to loss of contrast in video.

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.

VISIBLE RAY

Light whose wavelengths are visible to the eye.

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). Measurement sometimes expressed Greek symbol u which is equivalent to micron symbol mu. Millimicrons equal mu=m mu.

WIDEFIELD EYEPIECE

An ocular with an achromatic doublet for the eye lens and with the plane side of the lower lens nearest the objective. Such a corrected system does not have to be stopped down with a diaphragm, hence a large flat field is achieved. The y offer the greatest field of view when looking at specimens.

WORKING DISTANCE FREE

The distance between the front lens of the objective and the coverslip (or uncovered object) when the lens is focused on the specimen.

ZOOM

A lens system that provides for variable magnification capability while keeping the specimen in focus.