GLOSSARY OF TERMS

Aberration - an optical defect in the design of a lens. The lens does not bring all the rays of light to an exact focus. There are several different types of aberrations each having a contributing factor on image quality.

Achromat - A lens system that has been designed to reduce chromatic aberration. A photographic lens system is usually corrected to provide the same focal length for the red and blue wavelengths.

Achromatic - color-corrected optics used to produce true specimen color.

Achromatic Condenser - a condenser corrected for both spherical aberration. It is the most common type found on bright field microscopes.

Alignment - condition in which all optical elements are centered on the same axis.

Aperture - a fixed or adjustable opening or hole through which light may pass. Located beneath the microscope stage.

Apochromat - A lens system in which chromatic aberration is corrected for three or more colors. Apochromatic lenses are used in photoengraving applications and for telephoto lenses that have large maximum apertures.

Arm - part that serves as both the support of the body tube and its lens systems and as the held part of the microscope when it is carried.

Base - the weighted bottom of the microscope which gives it both good balance and resistance to unexpected movement , "vibration."

Body Tube - the main structure which holds the eyepiece and objectives at a precise distance to each other, and which allows this combined system to approach the stage into clear focus.

Brightfield - used to examine specimens which have contrast/color (i.e. stained histological specimens.)

Components - a brightfield condenser and brightfield objectives.

Disadvantages - cannot be used to view specimens of little or no contrast.

Brightfield Illumination - the ray of light incident upon the object is parallel to the optical axis.

CCD-Charged Coupled Device. This is the image detector in a video camera.

Chromatic Aberration - an optical defect of a lens, seen as color fringes or halos, which causes different wavelengths of light to be focused at different distances from the lens.

Coarse Adjustment - the knob which moves the specimen (or objective) rapidly, vertically for focusing.

Color Balance - a method of correcting a light source by way of filtration so that the light has optical characteristics similar to sun light.

Color Temperature - the quantitative value indicating the amount of color or colors emitted by an object.

Condenser - the lens system between the illuminator and the specimen which condenses the light and focuses on the specimen.

Confocal - an interferometric microscope utilizing a rotating aperture and a CCD image analysis.

Contrast - light and dark. To produce a good image, you must have good contrast as well as good resolving power (N.A.).

Corrected Lens - a lens or lens system which corrects for specific aberrations.

 Darkfield - used to examine specimens which cannot be distinguished from the background; (i.e. syphilitic spirochetes, silver grains in auto-radiography.)

Components - a dry darkfield condenser for low magnifications and any low magnification objectives. An oil darkfield condenser for higher magnifications. High magnification oil objectives must have an iris.

Darkfield Illumination - the ray of light incident upon the object is at an angel from the optical axis; therefore scratches and dents on the surface are illuminated while the other intact part remains dark.

Daylight Filter - a blue filter used to correct the color temperature of a light source.

Depth of Focus - range around the focal point in which the image is still clear.  The larger the N.A., the smaller the depth of focus.

Differential Interference Contrast - (Often called Nomarski)-used to examine round, multi-cellular, tubular or thick transparent specimens.

Components - DIC condenser, re-combination prism, DIC objectives.

A very specialized item and usually ordered for specific applications.

Disadvantage - price; cannot be used with plastic dishes.

DIN - Deutch Industrie Norm-international standard used in the manufacture of interchangeable objective lenses. A typical DIN type microscope utilizes 45mm objectives+160mm tube length for a 205mm system length.

Diaphragm - a rotary disk, located under the stage, whose graded opening allows a variety of angles of light to come up through the stage opening. Also available as a continuously varying diameter adjusted by a lever located on the side of the component.

Drawing Tube (Camera Lucida) - enables a person to view the specimen and the paper/pencil simultaneously for drawing.

Dual Viewing Attachment - enables two people to view the same specimen through the same microscope simultaneously.

Empty Magnification - magnification which increases the size, but does not increase the detail, due to the limitation of the resolving power of the optical system.

Eyepiece - the lens system closest to the eye. Magnifies the image produced by the objective. So, with a 10X objective and 10X eyepiece, the total magnification is 100X.

Eyepiece tube - a smaller diameter extension of the body tube which receives the eyepiece.

Eye Point - the location of the eye when using a visual instrument which allows for the best possible viewing.

Eye relief - the distance from the eye lens of the microscope to the eye point.

Fluorescence - use to locate fluorescently tagged material (protein, enzyme, gene) by illuminating the material with one wavelength of light in hopes that the fluorescence tag will appear by emitting this light at a different wavelength; i.e. FITC labeled materials in tissue when illuminated with blue light will emit with green light.

Components - Epi fluorescence attachment, a mercury (or other) light source, power supply, specialized filter systems, each one for a different fluorescent tag.

Disadvantage - Specimen is usually fragile, unstable and cannot be used for long periods or stored.

Fluorite - an objective corrected for two wavelengths and therefore, with a higher resolving power than an Achromat. (There are exceptions) Manufacturers call them Fluor, Neo-Fluor, Fluotar.

Field - the actual diameter of the viewing area, usually expressed in millimeters. As magnifying power is increased, the field of view is decreased.

Filter - a colored transparent material placed in the path of illumination to vary the conditions of viewing.

Filter mount - an existing slot on the microscope which can hold one of a set of filters in the path of illumination.

Fine Adjustment - the knob which moves the specimen (or objective) slowly, vertically for focusing.

Finity Correction System - an optical system in which the image is formed only by an objective lens.

Focal Length - distance between a principal point and a focal point.   f1 is a focal length of objective, f2 is a focal length of tube lens.  Magnification is determined by the ratio of objective lens focal length and tube lens focal length. (for Infinity correction system)

Focus Rack - part of the assembly (plus pinion) which specifically allows the distance from the objective lens to the specimen to vary, and therefore permit required coarse and fine focus adjustments.

Fully (Anti-reflective) Coated - coating of a lens which improves its ability to transmit light more efficiently. 

Hoffman Modulation Contrast - called the "poor man's" Nomarski. Used to examine the same types of specimens as DIC/Nomarski.

Components - Hoffman condenser, polarizer and Hoffman objectives.

Disadvantages- Loss of some resolving power.

Huygenian Eyepiece - an eyepiece which effects a certain amount of correction for chromatic difference of magnification in the achromatic objective lens.

Illuminating Mirror - usually a two-sided mirror on a rotating axis located below the stage. It reflects light up into the stage opening and onto the specimen.

Illumination - the supply of light onto the object under the objective lens.

Illuminator - the source of light which illuminates the object or specimen to be observed. May be fixed intensity, or variable.

Image Plane - a plane which is at right angles to the optical axis at the image point.

Inclination Joint - located at the base of the arm of some microscopes allowing the viewer to tilt the microscope at a more comfortable angle to look at dry slides.

Incline(30-45 degrees) - the eyepiece tube is manufactured at an angle to the horizontal to allow more comfortable posture during long periods of observation.

Infinity Correction System - an optical system in which the image is formed by an objective lens and a tube lens.

Interchangeable Eyepiece - a lens system which fits within the eyepiece tube and which is usually replaced by another lens of equal mounting diameter but of different magnification power.

Interchangeable Objective - a lens system threaded into the nosepiece turret which can be removed and which is usually replaced by another lens of equal mounting diameter and threading, but different magnification power. 

JIS Standard-Japanese Industrial Standard -international standard used in the manufacture of interchangeable objective lenses. A Typical JIS type microscope utilizes 36mm objectives+170mm tube length for a 206mm system.

Lens - optical glass which has two polished surfaces and is used to converge or diverge light rays.

Light - electromagnetic radiation.

Long Working Distance - usually an objective with a greater than normal working distance.

Used in micro-manipulation, inverted microscopy, producing micro instruments. A normal 40X objective will have a working distance of 0.06mm. A long working distance 40X will have 2.4mm; an extra long working distance 40X will have 10mm; a super long working distance 40X will have 15mm. The longer the working distance, the lower the resolving power..

Magnification - an enlargement of an object by an optical instrument. It is the ratio of the size of the image to the actual size of the object under observation.

Magnifying 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 microscope is larger than the object would appear to the unaided eye.

Micro-manipulator - used to inject or extract substances from the specimen. Also used to measure electric current produced by the specimen.

Microscope - a high precision optical instrument which uses light to observe objects. It is capable of high magnification and resolution and is used for making minute details visible.

Motorized Scanning Stages - used to allow a computer to control movement of the specimen. Highly specialized and rare at the moment but soon will become the "in" thing in combination with CCTV.

Multi-viewing Attachment - enables 2-8 people to view the same specimen through the same microscope simultaneously. 

N.A. - Numerical Aperture.  N.A determines resolving power, focal depth, and luminosity of the image.  The larger N.A., is, the higher resolving power and smaller focal depth are.

Nosepiece - a rotary turret mounting for the set of objectives.

Numerical Aperture (N.A.) - a number to represent resolving power of an objective.

Objective Lens - the compound lens system in a microscope which receives light from the field of view and forms the first image. The lens system closest to the specimen. Produces the primary magnification; i.e. 2X, 4X, 10X.

Ocular Micrometer - inserted in the eyepiece, it enables the person to measure the specimen.

Oil Immersion - a technique of placing special oil between positioned 100X objective and the glass slide on the stage to improve the resolving quality at high magnification. Also placed between the condenser and the glass slide.

Parallax - an imaging error introduced when using a stage micrometer of significant thickness. This is when the scale and the specimen appear to be in the same plane, thus causing incorrect measurements.

Parfocal - the ability to rotate the objective turret with minimal refocusing.

Parfocal Length - distance between the surface of the specimen and objective lens mounting position when in focus.

Phase Contrast - used to examine live, unstained specimens.

Components - Phase condenser and phase objectives.

Disadvantages- produces an optical artifact called the phase halo. It is, therefore, completely unusable for round, multi-cellular or tubular specimens. i.e. eggs, worms (nematodes), neurons.]

Photo-Micrographic Camera - Can only be attached to a trinocular tube.

Provides a clear focus, minimum to no vibration and great flexibility in interchangeability of film holders; i.e.-35mm. Polaroid 3 x 4 or Polaroid 4 x 5. Vary greatly in complexity and degree of sensitivity; (i.e. manual, semi-automatic or fully automatic.)

Photomicrography - the process of documenting images on film as seen through a microscope.

Plan Objective - an objective corrected for flatness of field so that when you view the specimen it is in focus all across the field. We then have Plan Achromats, Plan Fluorites, and Plan Apochromats.

Polarizing Components - can be added to an existing basic microscope to locate birefringent materials (i.e. crystals, etc.). 

Rack and Pinion - the intermeshing of a geared wheel and matching vertical grooved rack to develop tight accurate focusing.

Ramsden Eyepiece - an eyepiece similar to the Huygenian eyepiece. It differs in that it has its focal plane either on or just outside the surface of the collective lenses.

Real Field of View - range (diameter) of specimen observable with a microscope.

Resolving Power - the ability resolve two points at a given distance.

Rotational Viewing (360 degrees) - a microscope set up in such a way that the eyepiece and eyepiece tube can rotate around horizontally. Several people gathered around the same instrument can thus view the same specimen without moving, or having to move the microscope.

Scanning Electron Microscope - a microscope which uses a beam of electrons to impact the specimen. Secondary electrons emitted at the point of impact are imaged by high tech scanners.

Spherical Aberration - an optical defect in which the lens fails to form a sharp image. Rays of light which pass through a lens near its edge are converged to a point nearer the lens than those rays passing through the center of the lens.

Stage - the platform which hold the specimen.

Mechanical Stage - moves the specimen East to West and North to South.

Rotating Stage - usually rotates 360 degrees or, in the case of a rotating mechanical stage, as much as 270 degrees.

Stage Clips - fasteners located on the stage and placed over slides to hold them securely in place while viewing.

Stage Micrometer - used to calibrate the ocular micrometer.

Stand - the basic component of the microscope which holds all of the other components. Usually contains the light source (illuminator).

Stop Screw - an adjustable screw located at the base of the focus rack which, when adjusted properly, prevents the body tube from lowering too far and potentially causing damage to both the highest power objective and the specimen. 

Tube Length - the optical distance from the objective to the eyepiece. Governs interchangeability of optical components; i.e. a microscope objective corrected for 160mm. tube length cannot be used on a microscope corrected for infinity.

Turret-mounted - all objectives are attached to one common rotating nosepiece to allow for quick and accurate objective positioning during viewing.

Ultra-violet - the portion of the spectrum where the wavelengths are below the visible spectrum.

Video Microscope - enables the specimen to be viewed on a video screen. Image can also be analyzed by a computer.

Components - "C" Mount (interface between closed circuit TV cameras and microscope), CCTV Camera, monitor and possibly an image processor.

Disadvantages - Expense in the case of the more specialized systems only.

Virtual Image - an image that does not converge in real space.

Wavelength - light travels in waves varying in length. Measurement is from the top of one wave tot he top of the next one and is usually measured in units of nanometers (nm) or Angstoms (A).

Wide Field Eyepiece - an eyepiece having a large field of view with a high eye point.

Working Distance - the distance from the front element of the objective to the specimen.