Glossary
absolute alcohol
100% alcohol, used for dehydrating preparations. 98% anhydrous (water free) alcohol or acetone can be substituted.absorption of light
The taking in of light without reflection or transmission. In the case of colored filters, wavelengths of light that are not the color of the filter are subtracted (absorbed); light the color of the filter is transmitted. Also see: subtractive color mixture.achromatic doublet
A compound lens made with two lenses; one lens is made of crown glass, the other of flint glass. The two lenses are designed to correct each other's chromatic aberrations, usually of red and blue light. An achromatic doublet will also correct some spherical aberration of yellow light.achromatic optical systems
The standard optical system for microscopes. Chromatic aberrations are corrected in two colors, and spherical aberrations are corrected in one color.acid alcohol
A mixture of 95% ethyl alcohol and 2.5% nitric acid used for removing excess basic dye from specimens. A mixture of any alcohol and household acids often works well enough. Also see: basic alcohol, basic dye, acidic dye.acidic dye
A salt with a negative chromophore. Also see: ionic compound, chromophore.additive color mixtures
Color mixtures achieved by adding one light to another. Also see: subtractive color mixtures.additive primaries
Red, blue, and green are the additive primaries. All other colors of light in the visible spectrum can be created by combining lights that are the colors of these primaries. Also see: additive color mixtures.albumin
Egg white, used to paste tissue sections to slides. Some recipes mix in other ingredients such as glycerine or sodium salicylate, but plain albumin works well. Albumin is sold as a dry powder by biology suppliers. Whites from fresh eggs work well, but are inconvenient to work with. Some brands of frozen egg substitute are 98% albumin, and also work well.algae
Simple photosynthetic organisms that are predominately aquatic. Some algae are classified as protists, others as plants, depending on the classification system being used. Microscopists who keep aquaria will often encounter algae.amorphous
A solid without crystalline form. Most mounting mediums and the glass from which slides and cover slips are made are amorphous. Mounted specimens are therefore completely enclosed in amorphous substances.analyzer
A sheet of polarizing material that can be used to determine the direction of polarization of light coming through another sheet of polarizing material. As applied to microscopy, the sheet of polarizing material that is nearest the eye of the observer. The analyzer is rotated so that interference colors can be detected in the specimen. Also see: crossed polarizers.Animalia
The kingdom of multicellular animals that use a mouth to ingest organic matter. The cells are eucaryotic.annular brightfield illumination
Transmitted light illumination employing a small central stop. Darkfield illumination is set up in much the same way, but uses a larger central stop and cuts out all directly transmitted light.aperture diaphragm
The aperture just below the microscope condenser.apochromatic optical system
An optical system that is corrected almost perfectly throughout the entire visual spectrum. Apochromatic optics are available only on the most expensive light microscopes.astigmatism
Aberration in which rays striking the lens along right angled meridians focus in different planes.barreling
Aberration in which the center of an object appears too large and its periphery too small.basic alcohol
Alcohol in solution with a base. Speeds the process of destaining acidic dyes. A few drops of ammonium hydroxide (household ammonia) in 70% alcohol can be used. Many other formulas are available.basic dye
A salt with a positive chromophore. Also see: ionic compound, chromophore, acidic dye.birefringent
A kind of molecule, present in many substances, that has the ability to alter polarized light by causing double refraction. Also see: double refraction.bracketing
In photography and photomicrography, to take a number of exposures at graduated shutter timings. Bracketing is often necessary in photomicrography if you do not own some very expensive and specialized equipment.brightfield
Basic, transmitted light illumination. Standard microscopes come equipped for brightfield illumination.camera lucida
Device that aids in drawing by allowing the eye to see both the specimen and a superimposed view on drawing paper.Canada balsam
The classic resin for mounting specimens and cover slips to slides. Both damar varnish and synthetic resins are superior.centering telescope
An accessory used in place of the eyepiece to aid in centering the diaphragms in Köhler illumination.chemical microscopy
Microscopy of chemicals. A specialized polarizing microscope is required for advanced tasks.chromatic aberration
An aberration in which light of different colors does not focus at the same point.chromophore
The colored ion in a dye. Also see: basic dye, acidic dye, ion, ionic compound.ciliates
Single celled organisms of the kingdom Protista posessing short structures similar to flagella, called cilia.circularly polarized light
Light with a dual direction of polarization such that each direction of polarization lies at 90º to the other.cirri
Cilia fused into appendiges similar to legs. Posessed by certain ciliates.collimated light
Light traveling in parallel rays, as if from a source at an infinite distance.coma
The aberration in which rays striking the lens at an angle do not intersect correctly on the other side of the lens.compensator
A device that allows continuously adjustable retardation of polarization. Also see: retarder.complementary colors
Colors that lie opposite each other on the color wheel. Complements can be either additive or subtractive, depending on which color wheel is used.compound lens
Two or more lenses glued together or mounted mechanically in close proximity to one another. Also see: achromatic doublet.compound microscope
A microscope with an objective lens near the specimen and an eyelens fitted into an eyepiece near the eye. Also see: simple microscope.condenser
A lens or device that condenses light. When collimated light strikes a positive lens, the light comes to a focus on the other side of the lens. The plane of this focus is smaller and brighter than the light was before it struck the lens. Microscopes use condensers to get concentrated light to the specimen. Curved mirrors can also be used to condense light.contractile vacuole
Organelle used to regulate the amount of water in a cell. Contractile vacuoles work like small water pumps. Protists often have these organelles.counterstain
Some structures are more easily destained than others. Counterstaining takes advantage of this. An initial stain is applied and destained; then a second stain of a contrasting color is applied. Structures that destain well become the color of the second stain; those that do not destain well remain the color of the first stain.cover glass
Small thin sheet of glass used to sandwich the specimen to the slide.critical illumination
Illumination setup in which the image of the light source is focused in the plane of the specimen. Has been replaced by Köhler illumination for brightfield work, but is still used for darkfield and oblique illumination.crossed polarizers
Two polarizers arranged so that the transmission axis of the second is at right angles to the transmission axis of the first. Informally, the polarizer and analyzer will be crossed when the microscopist rotates the analyzer until the background of the specimen appears darkest. See also: analyzer, retarder, compensator.crystal violet
See gentian violet.crystallography
The study of crystals.crystallographic microscopy
Study of crystals with a microscope. Advanced tasks require a special polarizing microscope.cytosome
A mouthlike structure of protists.damar varnish
Varnish made from the natural resin gum damar, used for mounting specimens and cover slips to slides. See also: Canada balsam, synthetic resin.darkfield illumination
An optical contrasting technique that presents a bright specimen on a dark background.decolorization
See destaining.decreation
To dissolve the paraffin from the tissue sections that have been pasted to a slide by immersion in xylene or some other solvent for paraffin.destaining
The procedure for removing excess stain from a specimen by putting the specimen in several changes of a solvent for the stain. Also called decolorization and differentiation. Also see: acid alcohol, basic alcohol, basic dye, acidic dye.diatom
A member of the class Bacillariophyceae of algae. Diatoms are generally brown, even though they are photosynthetic. The cell wall, called the frustrule, is impregnated with silica. The grooves on the frustrule are sometimes used in evaluating microscope optics.differentiation
See destaining.diffraction
A phenomenon caused by light waves bending very slightly when passing the edge of an obstruction.DIN (Deutche Industrie Norm)
An industrial standard that specifies sizes for some microscope parts.double refraction
The creation of two refracted beams from a single material that has two distinct refractive indices. Also see: birefringent, polarized illumination, retarder, compensator.edge enhancement
A computer image enhancement technique used to set off edges or boundaries between objects.eucaryote
A cell with a nucleus bounded by a membrane containing genetic material.eyelens
The eyepiece lens closest to the eye.eye relief
The distance from the eyelens to the image of the aperture diaphragm. Eyepieces with a long eye relief are better for users who must wear eyeglasses. Such eyepieces are sometimes referred to as "high-eyepoint."field diaphragm
A diaphragm located just above the illumination source. Light passes through this diaphragm before reaching the aperture diaphragm that is located nearer the stage or condenser.field lens
The eyepiece lens closest to the objective.fix
To kill the cells in living organisms without disrupting their contents.fixative
The agent used for fixing. A solution of formaldehyde is a common fixing agent.flagellate
Swimming, photosynthetic algae that are classified as protists. Euglena is a common protist.flat field
See plan.fluorite elements
Optical elements that work with glass elements to provide chromatic correction over more of the visual spectrum than glass elements alone can correct. Only expensive optical systems have these elements.focal length
Neglecting the thickness of the lens, the lens to image distance for an object at infinity or the lens to object distance for an image at infinity. For condenser lenses, the distance at which parallel light rays entering the lens from one side meet on the other side. Focal length of a positive lens is easily tested by holding the lens up to the sun and moving a piece of paper up and down below it. When the light spot is smallest and brightest, measure the distance from the paper to the lens.food vacuole
An organelle of protists that surrounds food.Fungi
A kingdom of organisms composed of eucaryotic cells which, lacking chlorophyll, live mostly on dead organic matter produced by other organisms.funnel stop
A tube with a flared base that fits into the rear of an objective in order to reduce its numerical aperture. The flared base keeps the stop from falling into the objective and damaging the optics. Funnel stops are useful for photomicrography because a reduced numerical aperture results in greater depth of field. They are also useful for home-made darkfield work; reduced numerical aperture allows rays emerging from the condenser to be less steeply angled.gentian violet
A useful basic stain that can be found in most pharmacies. It can be used for both permanent and temporary mounts. Also called crystal violet and basic violet 3, and the brand name "Viogen." Also see: basic dye.H&E
The abbreviation for "hematoxylin and eosin." The most frequently used staining combination in histology.hanging drop preparation
A temporary mount in which a drop of liquid is suspended from a cover glass above the depression in a well slide. Hanging drop preparations are very useful for observing live organisms. Also see: well slide.histology
The science that seeks to understand the structure and function of cells and tissues of both animals and plants. Embedding, sectioning, and staining of tissues is often used for these investigations.incident light
Light that has reflected from a surface. Also called reflected light.India ink
A good negative stain, available to anyone, useful for both permanent and temporary mounts. Also see: acidic dye, negative dye.image enhancement
Computer imaging techniques used to change an image in such a way that certain kinds of structures become more easily visualized.interference colors
Colors created by the interaction of polarized light with birefringent molecules and an analyzer. Also see: analyzer, birefringent.interference contrast illumination
An optical contrasting technique. Some structures in a specimen cause some of the light passing through them to shift phase. Interference contrast illumination makes the phase shift visible. The illumination is closely related to phase contrast illumination, which also makes phase shifts visible.ion
Particles formed when an atom gains or loses an electron. Ions are electrically charged. Those with a positive charge are called cations. Those with a negative charge are called anions. Colored ions are called chromophores. Also see: chromophore, basic dye, acidic dye.ionic compound
Compounds composed of ions. Salts are ionic compounds. Also see: ion, basic dye, acidic dye.JIS
A Japanese industrial standard used for microscopes built in that country. Most of the world still uses the DIN standard.killing jar
Container used to kill small specimens such as arthropods.Köhler illumination
The brightfield illumination setup which gives the most possible contrast without loss of resolution.light table
Specialized tables used by optics designers for experimentation.linearly polarized light
Light with a single direction of polarization.maceration
The removal of the soft tissues from insects by soaking them in a strongly basic solution.magnifier
A lens or group of lenses that create an image of an object which is larger than the object. Positive lenses can be used as magnifiers. Also see: condenser.mechanical tube length
Length of the tube into which the objective and eyepiece inserts. Also see: optical tube length.metachromasia
A color change in a dye that occurs when the dye chemically reacts with the specimen. When metachromasia occurs in tissues, it is usually strongest in the granules in mast cells (a type of connective tissue) and in cartilage. Toluidine blue and crystal violet are two dyes that exhibit this phenomenon. Such dyes usually exhibit the phenomenon through certain pH ranges. For instance, crystal violet is highly metachromasic at pH of between 0.0 and 1.8, but reverts to its normal violet color as soon as the specimen is returned to a higher pH level.methylene blue
The most common of all basic stains for use in microscopy. Also see: basic dye, acidic dye.micromanipulator
Device for manipulating and working with small objects.micrometry
Quantification or measurement of microscopic objects. Anthony van Leeuwenhoek was the first micrometrist.microtome
A device used for cutting very thin slices of even thickness from an embedded specimen.Monera
(Also called Procaryote) The kingdom of organisms without a nucleus.mordant
A substance that is an intermediary between a mordant dye and the specimen.mordant dyes
Dyes that require a mordant to attach their molecules to the specimen.negative dye
Dye that forms a deposit around a cell or colors the background. Such negative dyes give an enhanced view of the cell's shape. Negative dyes are acidic. Also see: acidic dye, basic dye.negative lens
Lenses that are thinner in the center than at the periphery. These lenses disperse instead of condense light and make objects appear brighter and smaller.neutral density filters
Filters used to control light's intensity without changing its color. They are very useful in color photomicrography when dimming the microscope lamp might change the color of the light.numerical aperture
An expression of the light gathering capability of a lens.objective
The microscope lens closest to the specimen. Informally, the set of lenses closest to the specimen which are housed in a removable tube.oblique illumination
An optical contrasting technique which is closely related to darkfield illumination. In oblique illumination the shape of the aperture is changed so that light striking the specimen comes from one side instead of traveling directly upward from the light source.ocular micrometer
An eyepiece with a reticle used for micrometry. Also see: stage micrometer.optical contrasting technique
Apparent color and brightness changes in the specimen when using darkfield illumination, Rheinberg illumination, polarization, or any of several other specialized illumination techniques. Diffraction and interference usually account for the contrast.optical tube length
The distance between two adjacent focal planes. One of the focal planes is of the objective in the direction of the eyepiece, and the other is of the eyepiece in the direction of the objective. Also see: mechanical tube length.organelle
Structures within cells that are bounded by membranes. Only eucaryotic cells possess such structures.par focal
Capability of a microscope such that different objectives can be rotated into place without having the specimen go out of focus.par central
Capability of a microscope such that objects in the center of the visual field at one magnification will still be in the center when another objective is moved into place.particle theory of light
The theory that interprets light as being made up of particles instead of waves.petrographic microscopy
Microscopy of rocks and minerals. A specialized polarizing microscope is required for advanced tasks.pH
A logarithmic measure of acidity. PH 7 is neutral, pH below 7 is acidic, and pH above 7 is alkaline. PH ranges from 0 to 14. A pH change of an integer represents the previous number times ten increase or decrease in acidity. Microscopists should keep a supply of pH test paper handy; acidity measurements are often needed. The acidity of aquaria that contain microscopic organisms is important to the health of the organisms and must be tested regularly. Acidic dyes stain better at low pH, basic dyes stain better at high pH, and metachromatic dyes usually display metachromatism when used within a specific pH range (indeed, they are themselves pH indicators).phase
A particular point on a wave. For instance, two waves of the same shape would be out of phase if their high points did not coincide. The stage of progress of a cyclic movement.phase
An optical contrasting technique. Some structures in a specimen cause some of the light passing through them to shift phase. Phase contrast has found ways of making the phase shift visible. Phase contrast illumination is closely related to interference contrast illumination, which also makes the phase shifts visible.photomicrography
Photography with a microscope. Do not confuse photomicrography with microphotography. The latter is the making of very small photographs of objects of any size. You may find the distinction between these two terms to be relaxed in older works on microscopy.photomicroscope
A microscope used for photomicrography.photosynthesis
The use of light to create carbohydrates from carbon dioxide. Green plants and algae use photosynthesis.pincushioning
Aberration in which the center of a specimen appears too small and its periphery appears too large.plan optics
The characteristic of some microscopes that, when looking at a flat object, parts of the object at the edge of the visual field are almost as well focused as those in the center. Field curvature is minimized. Also called flat field optics.plano-convex lens
A lens that is flat on one side and convex on the other.Plantae
The kingdom of (usually) multicellular organisms that photosynthesize food.polarized illumination
An optical contrasting technique which uses sheets of polarizing material to create interference colors.positive lens
A lens with a center that is thicker than its periphery. Also see: condenser, magnifier, negative lens.precipitation of crystals
Crystals formed by a chemical reaction.procaryote
A cell which does not possess a nucleus. The genetic material of such cells is not enclosed in a membrane.Protista
The kingdom of the simplest organisms whose cells have a nucleus and organelles.protozoa
Unicellular eucaryotic organisms of the kingdom Protista. First discovered by Leeuwenhoek.pseudocolor
Image enhancement technique that substitutes a different color for each of several brightness value ranges.pseudopodium
A protrusion from a cell used for feeding and locomotion. Rhizopods (amoembas) and white blood cells in higher animals are typical cells capable of using these structures.reciprocity effect
The way in which contrast of black-and-white film and color balance of color film are affected by long exposure times. Reciprocity effect is a problem in photomicrography, where long exposure times are common.recrystallization
Dissolving part of a mass of crystals, using the undissolved crystals as seed crystals for a new mass.reflected light
See incident light.refraction
The bending of light by a lens. For instance, if rays of light diverging from a small object strike a positive lens, the light will be bent (refracted) so that it diverges at a more acute angle after passing through the lens. 230refractive index
The degree to which a medium bends light. The velocity of light through a vacuum divided by the velocity of light through the medium.relief
The degree to which a crystal or other object stands out from its background. Relief increases as the refractive index of the mounting medium increasingly differs from the refractive index of the crystal.research microscope
As used here, the most expensive light microscopes. Electron microscopes are also commonly used in research.resolving power
The ability of a microscope to produce a detailed image. Do not confuse this with magnifying power. Many cheap microscopes have great magnifying power, but do not produce a highly resolved image.retarder
Sheet that can be placed anywhere between the polarizer and analyzer to alter the character of the polarization. A 1/4 cycle retarder will change the linearly polarized light to circularly polarized light.reticle
A network of fine lines or hash marks in the focus of an eyepiece.Rheinberg illumination
An optical contrasting technique that is closely related to darkfield illumination. The darkfield stop is replaced by a dark color filter, and lighter color filters surround this dark filter. Rheinberg illumination results in an image with a background the color of the dark filter and foreground objects the color of the lighter filter.ring illuminators
Circular fluorescent tubes used to encircle the objective and light a specimen evenly.safranin - fast green
One of the most commonly used staining combinations for botanical tissues.seed crystal
A crystal that encourages the growth of other crystals.simple microscope
A microscope comprised of only a single lens -- for instance, a single lens magnifying glass. Also see: compound microscope.smear
A slide making technique used for both temporary and permanent slides that require the examination of liquids and objects dispersed in liquids. To make a smear, a drop of liquid on one slide is drawn along its length by another slide.smoothing
An image enhancement technique that can be used to remove noise created by glare in a microscopic image.spherical aberration
Aberration by which rays of light passing through the center of a lens tend to focus on a different plane than those passing through the lens near the periphery.spot plate
A plate that has a number of depressions of about one centimeter diameter. Used for staining specimens.spring loaded objective
An objectives which retracts when it comes into contact with the cover slip. Such objectives are also often oil immersion objectives.stage micrometer
A slide engraved or printed with a small scale. Used to calibrate ocular micrometers.stop
An opaque object or aperture placed anywhere in the optical system.sublimation of crystals
Crystals formed by conversion of a solid to a vapor.subtractive color mixtures
Color mixtures that occur when particular colors are removed (absorbed) from light. Also see: additive color mixtures.subtractive primaries
Red, yellow, and blue. All other colors can be created by subtracting these primaries from white light. Also see: subtractive color mixtures, additive color mixtures.supra staining
See vital staining.synthetic resin
A synthetic medium used for mounting specimens and cover slips to slides. It usually consists of acrylic resin dissolved in xylene or toluene.thresholding
Image enhancement technique used to highlight parts of an image that are near some brightness value.tint
In additive mixtures, a tint results when white light is added to a light of another color. In subtractive color mixtures, a tint results when proportionately less of the material that absorbs a color is used. For instance, when white paint is mixed with red paint, a pink tint will result because there is less of the pigment that absorbs all but red in the mixture.usable magnification
The range of magnification that can give acceptable resolution. Also see: resolving power.virtual image
An image formed by an optical system. In microscopes these images are much larger than the actual object.vital staining
To color organisms without killing them. Live organisms can be fed, immersed in, or injected with the coloring agent.wave theory
The theory that explains light as a wave traveling away from the light source. Also see: particle theory of light.well slide
Slides that have a depression that is large enough to surround a drop of water. Also see: hanging drop preparation.working numerical aperture
The numerical aperture of an objective as it is influenced by the closing of the aperture diaphragm.copyright © M. Brian Stevens, 1993, all rights reserved
No part of this book, including text and illustrations, may be reproduced; nor may they be hosted anywhere except at the author's domain --
http://www.mbstevens.com/
ISBN 0-9638839-1-7
Library of Congress Catalog Number 93-93667
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