Background About Microscopes 

Microscopes are scientific instruments designed to enlarge objects such as minute small living organisms. This makes microorganisms more visible to the naked eye which then makes them easier to study. The first microscope, invented by Antonie van Leeuwenhoek in the 17th century, was simple and only had two lenses. In modern times, there are many different types of microscopes with a variety of lenses that allow for different degrees of magnification.

In this article, we will be discussing the terminologies that are associated with a microscope.


Abbe Condenser – A dark tube that is used in conjunction with a microscope to produce an image of an object by adjusting the focus. This condenser is also used to control the amount of light entering the microscope’s optical system.

Binocular Head – A binocular head has two eyepieces for use by two different observers. These are often found in compound microscopes and some stereoscopes. 

Blank Mount – A blank mount is used to holding the objective lens of a microscope. It is typically attached to the microscope body using a tube that has a groove. This groove rests on top of the eyepieces.

Body Tube – A part of the optical system that contains one or more lenses, and is part of the body of the microscope. The eye-piece and objective lens is attached to its bottom end, with a mirror at its top end allowing light from above to pass through it. The body tube is the part of the optical system that is used to focus light. 

Bouvier’s Tube – A tube that has an inch-wide section of glass at its narrower end, and a groove at its other end. It is designed to allow light to pass through as shown in the diagram. This is usually used for viewing very fine structures. 

Condenser – A device that is used to focus light so that it can pass through the specimen. This is located near the top of a light microscope and is usually attached to a diaphragm to control the amount of light that enters. 

Cross Hair Circle – A device that consists of two fine intersecting lines inside of a circle used for centering objects under a microscope. 

Diaphragm – A circular opening that is used to control the amount of light entering the microscope’s optical system. 

Diopter – The unit of measure used to determine the magnification power of a lens. It is equal to the reciprocal of the focal length in meters. 

Eyepiece – An optical device consisting of a tube with lenses that allows for viewing things under magnification. The ocular lens is located at one end, and there may or may not be an objective lens at its other end. 

Field Of View – The area that can be seen at one time when using the microscope. This is based on the diameter of the objective lens being used. 

Field Stop – A device that is used to block out distractions in an image by narrowing the field of view. It consists of two components, a shoulder stop and a diaphragm. 

Focuser – A device that is used to adjust the distance between the light source and the specimen so that light can pass through it. This is usually controlled by a mechanism on either side of the microscope’s body tube. 

Focusing Knob – A circular device that is used to adjust the focus of an image. It may be located on either side of the microscope’s body tube using whichever hand is more comfortable for use by an observer. 

Huygenian tube – A type of eyepiece that has two plano-convex lens elements with the diaphragm between them. 

Iris Diaphragm – A plano-convex lens element placed at the entrance pupil of a microscope, with an iris diaphragm blade in between them that is used to control the amount of light entering. 

Limiting Magnitude – The lowest power setting on a microscope that allows for the user to see an image.

Magnification – The amount of enlargement that takes place when looking through a microscope. This is based on the ratio of the size of an object under a microscope to its actual size. 

Meyer’s eyepiece tube – An eyepiece tube that consists of two plano-convex lenses, and is used to view objects with high magnification. It can be adjusted for various magnifications by moving the top lens backward and forward until it is in focus.

Micrometer Disc – A circle with a radius of one-tenth of a millimeter on it that is used to measure the microscopic object being viewed. The micrometer disc is placed on top of the specimen and adjusted until there is no movement when turned. 

Mirror – A device that reflects light from one surface to another. This is used in a microscope’s optical system. A convex mirror reflects incoming light while a concave mirror reflects outgoing light. 

Numerical Aperture – A measure of the efficiency of a microscope’s objective lens that is based on the angle at which light can pass through it. 

Objective – A single lens in the microscope’s optical system that is placed closest to the specimen and used to magnify the image. 

Objective Lens – A lens that magnifies an image by gathering light from an object under a microscope. It is usually located at the top end of an eyepiece. 

Objective Power – The magnification power resulting from the objective lens in use.

Occlusion – A device that can be placed over the ocular lens to block out unnecessary light. 

Ocular Lens – The lens located at the top of a body tube that is used for viewing images. 

Phase Plate – A device that can be placed in between a light source and a specimen to change the phase of the light rays so they can pass through some objects without being refracted. It is used to enhance an image by viewing transparent objects. 

Phase Reticle – A device used to alter the phase of light by placing it between a microscope’s light source and specimen. It is commonly placed in between the objective and eyepiece lenses. 

Polarizing Filter – A filter that can be placed in front of the eyepiece lens to stop unwanted light. 

Power – A measurement of the amount of light detected by a microscope’s objective lens under a microscope. 

Parcentered – It reduces aberration by aligning all elements of the optical system on a single axis.

Plano-concave Lens – A lens that reflects light rays with parallel rays.

Plano-convex Lens – A lens that reflects light rays with parallel rays. It is used in an eyepiece to increase magnification or as an objective lens when it is placed in front of a specimen. 

Refractive Index – The measure of how much a light ray bends when passing through an object. This can be used to determine the thickness of an object. 

Relative Abbe Number – The ratio between a microscope’s actual focal length and its effective focal length when light is passed through it. 

Resolution – The smallest image that a microscope can magnify. 

Reticle/Reticle Lens – An eyepiece lens on a microscope that allows for viewing objects at different magnifications without moving the specimen or the reticle. 

Retractable Objective – An objective lens that can be used at multiple magnifications. 

Rotation Optical Path – A system where all elements of a microscope are attached to a single axis. 

Rheoscope – A device used to examine the inorganic matter by viewing it in polarized light. 

Rigid Hemisphere Lens – A half-spherical lens that is used as a condenser or objective lens. 

Secondary Mirror – A mirror that is used to either increase or decreases the magnification of an eyepiece, allowing the user to move between different magnifications without changing their eye position. 

Semi-spherical Lens – A lens with its center area removed, forming a hemisphere. 

Slit Lamp Microscope – A type of microscope that uses a beam of light similar to a slit lamp, but can utilize the magnification of microscopes. 

Specimen Stage – A device that allows for the movement of a specimen under magnification. 

Spherometer – A device used to measure the sphericity of a lens or surface. 

Spherical aberration – The blurring of light when it passes through a lens, commonly occurring because of the spherical nature of glass lenses. 

Stage Focus – Refers to a microscope that allows the specimen to be moved by stages, allowing for more precise focus. 

Stereoscopic Microscope – A type of microscope that can be used to produce a three-dimensional image by observing through a binocular head. It consists of two separate eyepieces, and two opposing ocular lenses placed one above the other. 

Step-Index Filter – A filter that is used in front of the eyepiece lens to block out unwanted light. 

Stratus VL – Computer software available from Nikon that allows the examination of microscopic images and videos. 

T-Mount Adapter – An adapter used to attach a camera to a microscope. Provides a connection point between the two devices. 

Transilluminator – An attachment that can be added to the bottom of a microscope to allow transmitted light (rather than reflected light) as in traditional microscopes.

Two-Handed Eyepiece – An eyepiece with the ocular lens located at its bottom end so that it can be used by two people simultaneously. 

Vacuum Attachment – The part of a stereomicroscope that is used to attach the microscope to a vacuum pump. 

Vacuum Stage – The part of a stereomicroscope that is used to mount the specimen in an area away from the eyepiece and illumination. 

Visible-Light Diaphragm – A circular device used for controlling the amount of light entering through an optical system. Wave Plate – A device used to change the orientation of light waves entering through the objective lens. It is used to increase the resolution of an image. 

X-Ray Microscope – A device used to take x-ray photographs of objects at high magnifications.

Zoom Eyepiece – An eyepiece that uses a zoom mechanism to alternately view at different magnifications without having to move closer or farther from the specimen.

Zernike Condenser – A device that focuses light with several small lenses in a series that are placed along a plane parallel to the optical axis. It is useful for viewing fields with greater depth and width.

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