Microscope Glossary

The following terms have been simplified and defined in order to enhance your understanding of the use and functions of the various components of both stereo and compound microscopes.  Arm:  The part of the microscope that connects the tube to the base.  When carrying a microscope, grab the arm with one hand and place your other hand under the base. Articulated Arm:  A type of stand that holds a microscope body.  The stand clamps to a table and has a variety of motion in three dimensions.  Base:  The bottom support of the microscope. Binocular Head:  A microscope head with two eyepiece lenses, one for each eye.  Body:  This term is used mostly with the low power stereo microscopes and it is the basic heart of the microscope without any type of stand or illuminators.  It usually includes the eyepiece and objective lenses but not the focusing block. C-mount:  This is an adapter used with various types of video cameras.  Usually, you unscrew the lens from the camera and screw in the adapter.  The adapter then connects to the trinocular port on the microscope. Coarse Focus:  This is the rough focus knob on the microscope.  You use it to move the objective lenses toward or away from the specimen (see fine focus). Coaxial Focus:  A focusing system that has both the coarse and fine focusing knobs mounted on the same axis.  Usually the coarse knob is larger and on the outside and the fine knob is smaller and on the inside.  On some coaxial systems, the fine adjustment is calibrated, allowing differential measurements to be recorded. Condenser Lens:  A lens mounted in or below the stage whose purpose is to focus or condense the light onto the specimen.   The higher power objective lenses have very tiny diameters and require concentrated light to work properly.  By using a condenser lens you will increase the Illumination and resolution.  Condenser lenses are not required on low power microscopes. Contrast Plate:  A circular opaque plate placed on the stage of a low power microscope.  One side is white, the other is black.  It can be flipped around depending on the coloration of your specimen. Cover Slip:  A very thin square piece of glass or plastic placed over the specimen on a microscope slide.  When used with liquid samples, it flattens out the liquid and assists with single plane focusing. Diaphragm:  Generally a five hole disc placed under the stage on a high power microscope.  Each hole is of a different diameter.  By turning it, you can vary the amount of light passing through the stage opening.  This will help to properly illuminate the specimen and increase contrast and resolution.  The diaphragm is most useful at the higher powers. Dual Head:  A microscope with a single eyepiece lens coming out one side and an additional single eyepiece tube coming either off the top or from the opposite side.  Dual heads are used so that a teacher can verify what a student is seeing or can be used for video or camera work.  It is not recommended that two students do a lab sharing a single dual microscope as it will get to be uncomfortable for the student using the top eyepiece. Eyepiece Lens:  The lens at the top of the microscope that you look into.  They are usually 10X but also are available in 5X, 15X and 20X.  Widefield lenses have a large diameter and show a wide area of the field of view.  Fine Focus:  This is the knob used to fine tune the focus on the specimen.  It is also used to focus on various parts of the specimen.  Generally one uses the coarse focus first to get close then moves to the fine focus knob for fine tuning.  Field of View:  Sometimes abbreviated "FOV", it is the diameter of the circle of light that you see when looking into a microscope.  As the power gets greater, the field of view gets smaller.  You can measure this by placing a clear metric ruler on the stage and counting the millimeters from one side to the other.  Typically you will see about 4.5mm at 40X, 1.8mm at 100X, 0.45mm at 400X and 0.18mm at 1000X.  See micrometer. Fixed Arm:  A type of stand used with low power microscopes.  The arm and body are integral parts of the microscope and connected solidly to the base.  Focus:  A means of moving the specimen closer or further away from the objective lens to render a sharp image.  On some microscopes, the stage moves and on others, the tube moves.  Rack and pinion focusing is the most popular and durable type. Head:  The upper part of the microscope that contains the eyepiece tube and prisms.  A monocular head has one eyepiece, a binocular has two (one for each eye), a dual head has two but they are not together, and a trinocular head has three, one which is generally used for a camera connection. Illuminator:  A light source mounted under the stage.  Three types of light are commonly used:  Tungsten, Fluorescent and Halogen.  Tungsten is the least expensive and most common.  Fluorescent is bright, white and runs cool and Halogen is very bright and white but gives off heat like tungsten. Immersion Oil:  A special oil used in microscopy with only the 100X objective lens (usually at 1000X total power).  A drop is placed upon the cover slip and the objective is lowered until it just touches the drop.  Once brought into focus, the oil acts as a bridge between the glass slide and the glass in the lens.  Inclination Joint:  Where the arm connects to the base, there may be a pin.  If so, you can place one hand on the base and with the other grab the arm and rotate it back.  It will tilt your microscope back for more comfortable viewing.  One drawback of tilting it back is that wet samples will run off the slide. Mechanical Stage:  A mechanical way to move the slide around on your stage.  It consists of a slide holder and two knobs.  Turn one knob and the slide moves toward or away from you.  Turn the other knob and the slide moves left and right.  Since everything is upside down on a (high power) microscope it takes some getting used to but it is very convenient to have one especially when observing moving specimens like protozoans or other pond water critters.  Microscopes either have the bolt on mechanical stage that can be added (to many models) at any time or the integral mechanical stage that comes built in to the microscope.  Micrometer:  Also called a micron it is the metric linear measurement used in microscopy.  There are 1000 microns in a millimeter.  If something is 1.8mm long then it can also be expressed as 1,800 microns long. Mirror:  Allows you to direct ambient light up through the hole in the stage and illuminate the specimen. Monocular Head:  A microscope head with a single eyepiece lens. Nose piece:  The part of the microscope that holds the objective lenses also called a revolving nose piece or turret. Objective Lens:  The lens closest to the object.  In a stereo microscope there are objective pairs, one lens for each eyepiece lens.  This gives the 3-D effect.  On a high power binocular model there is still only one objective lens so no stereo vision. Oil Immersion Lens:  An objective lens designed to work with a drop of special oil placed between it and the slide.  With oil, an increase in resolution will be noticed.    Also, see "Immersion Oil" above. Rack Stop:  Usually set at the factory, the rack stop keeps you from cranking the objective lenses too far down (damaging something).  If you are using a very thin slide, you may find that you can't get the high power objective lens close enough to the slide to focus.  Here you can either adjust the rack stop or place a thin glass slide under your original slide, making it closer to the lens. Resolution:  The ability of a lens system to show fine details of the object being observed. Ring Light:  An independent light that usually connects to the microscope body and gives off a ring of light.  Semi-Plan Lenses:  Lenses are never perfect.  If you were looking at something perfectly flat, you might find that much of the center part of your field of view is in focus but out on the edges it is fuzzy and a bit out of focus.  Semi-plan lenses improve this deficiency by showing sharper images and less aberrations in the perimeter of the field of view.  They are better than standard achromatic lenses but cost quite a bit more. Slide:  A flat glass or plastic rectangular plate that the specimen is placed on.  It may have a depression or well to hold a few drops of liquid. Slip Clutch:  When students bring the focus all the way up or down and continue to try turning the knob, damage to the focusing system can occur if there wasn't a slip clutch.  It is a mechanical device that protects the gears of the microscope. Stage:  The flat plate where the slides are placed for observation. Stage Clips:  Clips on the stage used to hold the slide in place. Stage Plate:  On a low power microscope, there is a frosted circular glass plate that fits in over the lower illuminator.  This is called the stage plate.  See also contrast plate. Stand:  On a low power microscope, the type of connection between the microscope body and the base.  There are three main types:  the post, the fixed arm and the universal boom stand.  T-mount:  A type of adapter used to mate still cameras to microscopes Tension Adjustment:  This is an adjustment of the focusing mechanism that is made at the factory.  It is set so that the instrument is easy to focus but also tight enough so that the stage doesn't drift when you are not focusing. Stage drift is caused by the weight of the stage automatically unfocusing the microscope. Trinocular Head:  Available on both high and low power microscopes, tri heads have two eyepiece lenses and a third port at the top for a camera.  Some microscopes give you the option of sending all the light to the tri port. On some stereo tri heads with dual power, the tri port transmits the image through the set of lenses not being used by the stereo eyepieces. Widefield eyepiece lenses:  These are wide diameter glass eyepiece lenses.  They offer the greatest field of view when looking at specimens.  X:  Times as in 200X or two hundred times magnification.  The magnification of a microscope is determined by multiplying the power of the eyepiece lens by the power of the corresponding objective lens.