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Glossary of Microscopy Terms

Abbe Condenser- see condenser
Abbe ErrorAdditional linear off-axis error introduced through amplification of tilt and wobble with a long moment arm. This type of error occurs when the point under measurement is a relatively long distance from the axis of motion. For example, XYZ stages incorporating an angle bracket between the moving elements will exhibit measurable Abbe error since the Z stage is significantly displaced above the X and Y axes. It appears as runout, but unlike true runout, Abbe error can be minimized by reducing the lever arm.
Aberration- see chromatic and spherical
Achromatic- term referring to the lens. A lens which brings in light from two parts of the spectrum (red and blue wavelengths) to the same focus, reducing Chromatic Aberration. This is the most common lens on a microscope. Color fringes may appear when viewing under bright white light because not all wave lengths are brought within an acceptable focus range. If you use filtered light (monochromatic) as in phase contrast the image will be sharper.
Analyzer- see polarizer
Barrel Focus- the body tube of the microscope moves to focus the objective lenses and the stage is fixed.
Bertrand Lens- in polarizing microscopes a special lens used to view interfaced figures.
Brightfield Illumination- bright white light which illuminates a transparent or translucent specimen which appears dark against a bright or white background.
Body Tube Length- the distance between the objective and the top of the body tube, usually 160mm. Objectives are designed for a specific length, if miss-matched, spherical aberration will occur.
Coaxial- focusing system where the coarse and fine focus are mounted together on a common axis.
Condenser (substage)- provides an even cone of light that illuminates the specimen. Light from the condenser converges on the specimen, passes through it, and diverges to from an inverted illumination cone that is captured by the objective lens. The Abbe condenser is the most common. The condenser numerical aperture (NA) should be equal to or greater than the highest objective NA., usually 1.25 to 1.32 for a 100x oil objective. The resolving power of the optical system composed of condenser, objective ocular lens is limited to the lowest NA of its individual components.
Chromatic Aberration- failure of lens to bring light of different wavelengths to a common focus . This can be compensated by using an achromatic lens.
Crossed Roller WaysCrossed rollers define a way by fitting cylindrical rollers between hardened "v" ways. Every other roller is rotated 90 degrees, resulting in a symmetrical load bearing capacity. The line contact resulting from the roller-to-v fit provides a load bearing capacity of about an order of magnitude above that of ball ways. Roller retention and preloading are similar to those of ball way designs. Crossed roller designs provide moderate and uniform friction, high load bearing capacity, high linear and torsional stiffness, moderate cost, and very good straight line accuracy.
Darkfield Illumination- An optical technique where the specimen is seen as a bright object against a dark background.
Depth of Field- the distance along the optical axis throughout which the object can be located and yet be imaged with satisfactory clarity. This is used in stereo microscopy.
Differential Interference Contrast (DIC) A mode of contrast generation in microscopy that yields an image with a shadow relief. The relief reflects the gradient of optical path difference. DIC, which is a form of interference microscopy that uses polarizing beam splitters.
Diopter Adjustment- adjustment ring of the eyepiece that fine focuses the eye lens element.
Disc Diaphragm- a circular disc, located under the stage platform containing five or six apertures of various sizes which controls the size of illumination cone converging on the specimen.
DIN- a term referring to optics which is the abbreviation for Deutsche Industrie Normen, an industry standard for optics.Eyepiece- also known as ocular, it produces the second stage of magnification enlarging the image magnified by the objective lens. Eyepieces vary in magnification from 5x to 30x. The standard is 10x.
Eyepiece Diaphragm- the piece inside the eyepiece which holds gracticules and reticules. It also defines the round field of view that is seen through the microscope.
Field-Of-View- the visible area through the eyepiece when the microscope is in focus.
Flat Field Objectives or Optics- lenses which are corrected to eliminate curvature. Flat field optics are a higher grade then achromatic.
Flatness of TravelDeviation from ideal straight line travel in a vertical plane, also referred to as vertical runout.
Huygenian- a type of eyepiece that has two planoconvex lens elements with the eyepiece diaphragm between them. Usually with a narrow field of view.
Immersion Objective- most common is the 100x oil objective. Oil is placed on the cover glass of the slide which (and sometimes on the top element of the condenser) to produce a high magnification and high resolving power of the objective when immersed in the oil. This produces the full NA of objective lens.
Iris Diaphragm- usually mounted under the condenser this controls the amount of light converging on the specimen by opening or closing the leaf diaphragm.
Koehler Illumination- a technique for uniformly illuminating a field from non-uniform light such as a coiled filament lamp.
Magnification- the enlargement of an object through the lens system. This is determined by multiplying the magnifying power of the objective by the eyepiece.
Magnifying Power- magnification, which is the ability of the lens to make an object appear larger. It is the number of times the image is seen through the microscope is larger than the item appears to the unaided eye.
Mechanical Stage- a device on the platform for holding and moving the slide (or specimen) on an X or Y axis.
Micrometer Disc- a glass disc with a scale or grid mounted to the eyepiece diaphragm used for measurement.
Numerical Aperture- (N.A.) a term representative of the angle included by a cone of light accepted by the objective of a microscope. The higher the N.A., the greater the resolving power.
Objective lens- forms the primary image of the microscope which is seen through the eyepiece. The markings on the objective lens are the magnifying power (such as 10x), followed by the NA (0.25) and the tube length. Other numbers which appear on the objective lens may refer to the manufactures catalog number of the particular item.
Oculars-see "eyepiece"
OrthogonalityThe degree of perpendicularity, or squareness, between the two axes in an X-Y or X-Z table This parameter is usually measured in arc-seconds or microradians.
Parcentered- When all the elements of the optical system are aligned on a single axis thus reducing aberration.
Parfocal (parfocality)- a term used describing the property of a microscope where the subject stays in focus when the objective lenses are changed. Less then 1/2 of a revolution from the fine adjustment is usually acceptable.
PitchAn angular deviation possible in positioning systems, in which the tables� leading edge rises or falls as the table translates along its direction of travel. This represents rotation around a horizontal axis, perpendicular to the direction of travel.
Planachromat- an achromat lens which has been corrected for a flat field.
Planoconcave Mirror- a two sided mirror 50mm in dia., with one side flat (plano) and the other curved, (concave). The concave side is used for low NA when no condenser is used, the plano surface is used with a substage condenser.
Phase Contrast- the optical technique used to view the structure of transparent objects whose varying but invisible differences in thickness result in differences in the phase of transmitted light. This is done when the transmitted light changes its optical path by about 1/3 wavelength.
Polarizer- transparent material which can absorb all vibrations of light passing through it except those in a single plane.
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), usually moves the barrel or stage.
Refractive Index (R I )- the ratio of the speed of light in a vacuum to its speed in some other medium. This will determine how much light rays are bent. When using immersion objectives it is important to keep the values as close together as possible.
Resolution- a measure of the ability of a lens to image closely spaced objects so they are recognized as separate objects.
Resolving power- the capacity of any optical system to distinguish and separate details in a specimen.
Retractable Objective (XR)- usually on the 40x and 100x objectives, a spring is loaded inside the objective so that minimal damage is done to the slide and the top element of the lens should it be racked down beyond its normal stop.
RunoutThe linear (versus angular) portion of off-axis error. It is the deviation between ideal straight line motion and actual measured motion in a translation stage. Runout has two orthogonal components, straightness, a measure of in-plane deviation, and flatness, the out-of-plane deviation.
Spherical Aberration- the failure of a lens system to image the central and peripheral rays at the same focal point
.Stage- the platform on the microscope where the slide or specimen is placed. The stage may be square, circular, fixed, rotating or even interchanged.
Stage Focus- a specific type of focus where the stage moves and the body tube is stationary when focusing.
Straightness of TravelDeviation from straight line motion in a horizontal plane. Also referred to as horizontal runout. This error is usually traceable to an underlying angular error of the ways.
Tilt and WobbleThe angular portion of off-axis error. It is the deviation between ideal straight line motion and actual measured motion in a translation stage. Tilt and wobble have three orthogonal components commonly referred to as roll, pitch, and yaw. These terms usually dominate the overall error due to the geometry of the motion system.
Widefield Oculars (eyepieces)- a term referring to the size of the field of view on the ocular. A wide field ocular may be 19-21mm compared to a lower measure.
Working Distance- the distance between the cover glass or object and the tip of the objective. This governs the allowable movement of the objective in obtaining critical focus of the specimen.

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YawAn angular deviation from ideal straight line motion, in which the positioning tables rotates around the Z (vertical) axis as it translates along its travel axis.
Zoom- a lens system that provides for variable magnification capability while keeping the specimen in focus.

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