GLOSSARY OF TERMS

 

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

 

 

A

Aberration

An optical effect.  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 to image quality

Achromatic

Colour corrected optics used to produce true colour

Achromatic condenser

A condenser corrected for spherical aberration.  It is the most common type found on brightfield microscopes

Achromatic lens 

A lens system that has been correct to provide the same focal length for the red and blue wavelengths of light. The result is an image virtually free for extraneous colouring or aberrations

Alignment

A condition in which all optical elements are centred on the same axis

Analyser

The part of a polarisng system that can select on angle of light and is used in conjunction with a polarising filter

Aperture

A fixed or adjustable opening or hole through which light may pass through

Apochromat

A lens system in which chromatic aberration is corrected for three or more colours

Apochromat lens

An apochromatic lens system can correct for three colours instead of two.  This type of lens also has less spherical aberrations

Arm

The part of the microscope that serves as both the support of the body tube and its lens systems.  The part held when microscope is carried. Also sometimes referred to as limb

 

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B

Base

The weighted bottom portion of the microscope which gives it both balance and resistance to unexpected movement or vibration

Beamsplitter

A device that allows light to be split into two paths, usually comprised of a piece of glass wth special coatings mounted at a 45 degree angle from the input source 

Binocular

A microscope head that has an eyetube for each eye 

Brightfield

An illumination method in which light is reflected off the specimen and passed through the objectives to the eyepieces 

 

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C

CCD

Charged Coupled Device.  This is the image detector or chip inside a video camera.  CCD's are categorised by their diagonal size like 1/3", 1/2", 2/3", etc.

Chromatic aberration

An optical effect of a lens characterised as colour fringes or halos.  They are caused by different wavelengths of light focusing at different distances form the lens

Coarse adjustment

The control knob which moves the specimen (or objective) rapidly allowing focusing to occur

Colour temperature

The quantitative value indicating the amount of colour or colours emitted by an object, measured in Kelvins.

Condenser

The lens system between the illuminator and the specimen which condenses the light onto the specimen

Contrast

The ratio of light and dark.  To produce a good image, you must have good contrast as well as good resolving power

Corrected lens

A lens or lens system which corrects for specific aberrations

 

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D

Darkfield

An illumination method used to examine specimens which cannot be distinguished from the background. Components include a dry darkfield condenser for low magnifications and any low magnification objectives.  An oil darkfield condenser is used for higher magnifications.  Higher magnification oil objectives must have an iris.

Daylight filter

A blue coloured filter used to correct the colour temperature of a light source

Depth of field

A short distance along the optical axis throughout which the specimen can be seen with sufficient clarity

Depth of focus

A short distance along the optical axis throughout which the specimen is focused sharply

DIN

Deutch Industrie Normen - an international standard used in the manufacture of interchangeable objective lenses

Disc diaphragm

A fixed rotary disk, located under the stage of a student grade microscope, that has graded openings that allow various angles of light to come up through the stage opening

Drawing tube

(Camera Lucida) - this device enables a person to view the specimen and paper simultaneously for drawing superimposed image

Dual viewing attachment

Enables two people to view the same specimen through the same microscope simultaneously

 

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E

Empty magnification

Described as 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.  Also referred to as "oculars"

Eyepiece tube

Tubes of the microscope head which hold the eyepiece

Eye point

The location or position of the eye which allows for the best possible viewing of the image

Eye relief

The distance from the vertex of the eyepiece lens to the user's eye at the eyepoint

Exit pupil

Exit pupil describes the image that is projected to a particular point in space beyond the eyepiece.  Your eye must be positioned in that exact location in order to see the full, clearly focused image.  The exit pupil is a dimension usually expressed in millimeters

 

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F

Fluorescence

An illumination method used to locate fluorescently tagged material (protein, enzyme and gene) by exciting the material with one wavelength of light in hopes that the fluorescence will appear by emitting a light at a different wavelength

Fluorite

An objective corrected for two wavelengths and therefore, with a higher resolving power than an achromat.  There are exceptions as some manufacturers call them Fluor, Neo-Fluor, Fluotar and others

Field

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

Filter

A coloured, 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 filters in the path of illumination

Filar eyepiece

An eyepiece with an integrated measuring reticule and a moveable crosshair for making measurements on a microscope

Fine adjustment

The control knob which moves the specimen (or objective) very slowly allowing microtonal focusing to occur

Finity correction system

An optical system whereby the image formed is made solely by an objective lens

Flatness of field

A quality describing the appearance of the field of view as being flat from edge to edge

Focal length

The distance from a point where an image is formed to a point in the lens system

Focal point

A point in which light rays converge after passing through a lens

Focus rack

The part of the microscope which allows the distance from the objective lens to the specimen to vary and to accomplish coarse and fine focus adjustments

 

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H

Huygenian eyepiece

An eyepiece with correction for chromatic difference of magnification in the achromatic objective lens

 

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I

Illumination

The application of light onto an object or specimen under a microscope

Illuminator

The source of light which illuminates the object or specimen to be observed.  It may have fixed intensity or variable intensity via a control knob

Incline

Eyepiece tubes are manufactured at an angle (30-45 degrees) to allow more comfortable posture during long periods of observation

Infinity correction system

An optical system by which the image is formed by an objective lens and a tube lens working in tandem

Interchangeable eyepieces

Microscope eyepieces are removable and can be exchanged with higher or lower powered eyepieces

Interchangeable objective

An objective that either threaded into a nosepiece turret or mounted on a dovetail that is removable and that can be replaced by another objective with a different magnifiction power

Iris diaphragm

A device which can open and close like the iris of the eye.  On a microscope this diaphragm is located under the stage and can be adjusted by a lever located on the side of the component

 

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J

JIS

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

 

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K

Koehler illumination

This type of illumination was introduced in 1893 by August Kohler as a method of providing the optimum specimen illumination

 

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L

Lens

An optical grade glass which has two polished surfaces and is used to converge or diverge light rays

Long working distance

Usually refers to an objective or a microscope with a greater than normal working distance

 

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M

Magnification

The enlargement of an object by an optical instrument

Magnifying power

The metric of a lens or combination of lenses to make an object appear larger is called magnifying power.  It is the number of times the image is larger than the object would appear to the unaided eye

Microscope

A 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

Monocular

A microscope head with a single eyepiece

 

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N

N.A. Numerical Aperture

N.A. is a combination of resolving power, focal depth and luminosity of the image.  The larger the N.A. value, the higher the resolving power and the smaller the focal depth

Nosepiece

A rotary turret mounting for a set of objectives

 

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O

Objective lens

The compound lens system in a microscope which receives light from the field of view and forms the primary image.  The lens system closest to the specimen is the objective lens

Ocular micrometer

When an ocular micrometer is inserted in the eyepiece, it enable the person to take measurements of a specimen.  It is also known as an eyepiece micrometer

Oil immersion

A technique of placing a drop of oil between a 100x objective and the coverslip in order to improve the resolving quality of the objective.  It also can be placed between the condenser and the glass slide.

 

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P

Parfocal

The ability to rotate the objective turret without refocusing.  With stereomicroscopes, parfocal is the ability to zoom throughout the magnification range without refocusing.

Parfocal length

The distance between the surface of the specimen and objective lens mounting position while the specimen is in focus

Phase contrast

An illumination technique used to examine live, unstained specimens that have poor contrast or are translucent

Photomicrography

The process of documenting images on film/digital as seen through a microscope

Photo port

Any port other than an eyetube which is exclusively used to connect cameras to 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 image field.  There are also plan achromats, plan fluorites and plan apochromats

Polariser

A filter which can produce polarised light and is usually used in conjunction with an analyser

Polarised light

Light waves which are uniformly aligned in one direction

Polarising components

Components that can be added to an existing basic microscope to locate bi-refringement materials

Prism

A solid piece of optical glass that has at least two plans inclined towards each other from which light can be reflected or refracted

 

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R

Rack and pinion

A mechanical design involving the intermeshing of a geared wheel and matching vertical grooved rack used in focus mechanisms

Ramsden eyepiece

An eyepiece similar to the Huygenian eyepiece, however it has its focal plane iether on or outside the surface of the collective lenses

Reticule

A piece of glass with a pattern printed on one side that installs into an eyepiece which allows the pattern to be imposed on the microscope's field of view

Resolving power

The ability resolve two points as two points at a given distance

Rotational viewing

A microscope set up in such a way that the eyepiece and eyepiece tube cna rotate around horizontally.  Several people gathered around the same instrument can thus view the same specimen which moving around or having to move the microscope

 

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S

Spherical Aberration

A spherical aberration is an optical defect by 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 centre of the lens.

Stage

The platform which holds the specimen.  Types include: plain, mechanical, motorised, heated etc.

Stage - mechanical

Moves the specimen East to West and North to South via X-Y controls

Stage - rotating

Can usually rotate 360 degrees or, in the case of a rotating mechanical stage, rotate as much as 270 degrees

Stage clips

Chrome metal fasteners located on the stage and placed over slides to hold them securely in place while viewing

Stage micrometer

Used to calibrate an eyepiece micrometer

Stand

A basic component of the microscope which holds all the other components and 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 high power objective and the specimen

 

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T

Teaching head

An accessory that allows more than one user to see into the microscope simultaneously

Trinocular

A microscope head with two eyepieces and a photo port

Tube length

This is the optical distance from the objective to the eyepiece.  Tube length governs the 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

Objectives that are attached to one common rotating nosepiece that allows for quick and accurate objective positioning during viewing

 

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U

Ultra-violet

The portion of the spectrum of light where the wavelengths are above the visible pectrum

 

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V

Video microscope

Enables a specimen to be viewed on a video screen. Image can also be analysed by a computer using image analysis software

Virtual image

An image that does not converge in open space

 

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W

Wavelength

Light travels in waves varying in length.  The measurement of a light wave is from the top of one wave to the top of the next one and is usually measured in units of nanometers (nm) or Angstroms (A)

Widefield eyepiece

An eyepiece having a large field of view with a high eyepoint

Working distance

The distance from the objective to the specimen with the image in focus

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