A
Aperture – The size of a hole that light passes through.
B
Barlow Lens – An auxiliary lens that is usually screwed onto the objective lens of a stereo microscope. They are used to alter the magnification of the built in zooming objectives. Most companies have 0.5x lenses to half the magnification and increase the working distance, and 2.0x lenses to do the opposite.
Binocular – This refers to the number of eyepieces available on a given microscope. It uses the prefix “bi” for “two” with the suffix “ocular” for “being of the eye,” meaning it has two ocular tubes to view with.
C
Compound Microscope – An instrument used for magnifying small objects using convex lenses. A lens of short focal length is used (an objective), and then further enlarged by a lens with a larger focal distance.
Concave Lenses – A lens having at least one surface curved like the inner surface of a sphere. This type of lens scatters light, and is what is used in a telescope to view distant objects.
Condenser – A lens underneath the stage of the microscope which serves to help focus the light from the light source onto the sample. This generally allows for a greater range of adjustments to be made to the angle of the cone of light for optimizing
Convex Lenses – A lens having at least one surface that curves outward like the exterior of a sphere. This type of lens focuses the light to a point, and is what is used in microscopes to create magnification.
D
Diaphragm (Disc) – A rotating disc underneath the microscope stage that allows to user to select different apertures of light, acting as a cost effective control over the angle of the cone of light approaching the objective. Setting this to just larger than the aperture of the microscope provides the most even illumination and ideal image.
Diaphragm (Iris) – A device like a shutter on a camera, this allows the user to control the angle of light that is being shined up into the objective. It is usually controlled by a lever, and a series of plates converge onto a point, or out to a larger circle. Adjusting this to allow a cone of light as large as just the aperture of the objective provides the most even illumination and optical quality.
E
Empty Magnification – This is magnification achieved through using a more powerful eyepiece rather than a higher power objective. Increasing objective power increases resolution, so you can see fine details in a small sample. If you use greater than 10x eyepieces, you are enlarging an image, but not adding any extra resolution, so the image will simply be bigger, but not more detailed. 1000x magnification is the highest optical microscope magnification than be achieved without using empty magnification.
Eyepiece – This is the second lens of a microscope which is what one looks through. 10x magnification is common for eyepieces, as this allows for the user to see the image enlarged close to the eye without adding any resolution issues. Without an eyepiece installed on your microscope, the image would appear to be far away, as if looking down a straw. Not installing eyepieces is a common new user mistake, so be sure that you have yours installed when using your microscope for the first time.
Exposure – This is the amount of light allowed per frame captured in a digital microscope camera. The higher the exposure, the longer the camera sensor collects light before displaying an image. Too high and the image is washed out, while too low and the image is too dark.
F
Field of View – The size of the area that you see through the microscope. The more magnification you use, the smaller your field of view becomes (the image is magnified, so the image is made bigger, but the aperture you’re looking through is the same size, so it’s like looking through a window where the window does not change size, but the image inside it does).
Focal Distance – This is the distance between the lens and your sample, and also called working distance. The more magnification used in a microscope, the less working distance is available, as you have to move your microscope objective closer to the sample to achieve a focused image. Likewise, the less magnification used, the longer your working distance becomes. This is critical for stereo microscopes where the user needs to operate with tools under the microscope, or for compound microscope users that wish to use large glass medium like petri dishes or beakers.
Focus – The point at which rays of light converge onto a single point. In a microscope, this is the point where the image is in clear view.
Focusing Knob – Knobs on the microscope used to adjust either the height of the stage on it, or the position of the head. Used to change focal distances until an image comes into clear view.
Framerate – This is the rate at which an entire digital image is refreshed to a new one. Commonly measured as frames per second (fps). The higher the fps, the more quickly the camera or screen updates the image, and the smoother the image becomes. Live imagery is typically achieved at around 60 fps.
G
Gain – Increase in the strength or amplitude of a signal as it traverses a circuit or material. Essentially another way to brighten up a digital image.
H
High Power Microscopes – Microscopes that typically start at 40x magnification and can reach up to 1000x magnification with full resolution, or higher with empty magnification. These are used for slides most commonly, however metallurgical microscopes are known to have high magnification values as well.
I
J
K
Kohler Illumination – A method of illumination of microscopic objects in which the image of the light source is focused on the substage condenser diaphragm and the diaphragm of the light source is focused in the same plane with the object to be observed; maximizes both the brightness and uniformity of the illuminated field.
L
Light Source – The illuminating element in your microscope setup. This can be anything from a mirror and the sun, to an LED, halogen, or mercury bulb lighting system.
Low Power Microscopes – Microscopes that generally start as low as 2x and can reach up to 225x (with limited working distance). Stereo microscopes fall into the low power category, and are usually used for larger, opaque samples for inspection or working on.
M
Mechanical Stage – A stage on the microscope which is mechanized to allow movement of the sample without touching it. This also serves to provide a measurable accuracy and precision. This can be either a clip on to the stage for X and Y motion, as the Z is controlled by the focusing knobs on the microscope.
Microscopy – The technical field of using microscopes to view samples and objects that cannot be seen with the unaided eye (objects that are not within the resolution range of the normal eye).
Monocular – This refers to the number of eyepieces available on a given microscope. It uses the prefix “mono” for “one” with the suffix “ocular” for “being of the eye,” meaning it has a single ocular tube to view through.
N
Numerical Aperture (NA) – Numerical Aperture is a value used to grade the resolution capabilities of a microscope objective.
It is calculated by NA = n(sin m).
“n” is the refractive index of the medium between the front lens of the objective and the cover slip on the slide. In plain English, this is a number determined by what is between the lens and the slide, which is typically air (with a value of 1.00), or immersion oil (values range around 1.51).
“m” is one half of the angular aperture of the objective lens. This means that it is half of the angle of light that will hit the lens when shining from the bottom (light shines in a cone shape, not a beam). Too large of an angle and light is wasted by not entering the objective, and too little won’t be bright enough to illuminate the sample area.
“sin m” then is what determines the NA rating in situations where air is the medium. When we take the whole formula into consideration, the max value of sin m is 1 (sin 90° = 1). Therefore, the max NA rating for a dry objective (air medium) is 1.00 (refractive index is 1, sin 90° is also 1, 1 x 1 = 1).
It gets a bit more complicated for oil medium however, but the highest NA rating I’ve seen on the common microscopes I use is 1.25 NA.
O
Objective – A convex lens with a short focal distance used to magnify samples. This is the lens closest to the sample.
Ocular Tube – A tube or hole on a microscope designed to accept an eyepiece or camera.
Opaque Samples – These are subjects under a microscope that cannot pass light through. Reflected light is needed to visualize them (and a microscope capable of viewing reflected light).
P
Prism – A transparent solid body, often having triangular bases, used for dispersing light into a spectrum or for reflecting rays of light. Used to reflect rays of light in a microscope from the objective up to the eyepieces.
Q
R
Reflected Light – Light that is emitted from a light source on the top of a microscope that bounces back off of a solid object. This is used for opaque objects, and is common for all stereo microscopes and metallurgical microscopes.
Resolution (Digital) – The amount of pixels that make up your digital image when using a computer or digital device with a screen.
It’s generally thought that the higher resolution (measured in pixels, or more commonly in megapixels), the clearer your image is, however this has diminishing returns. The human eye cannot generally tell the difference between resolutions above 5 megapixels when looking at a screen (which further depends on the display resolution of the screen). If an image resolution is larger than the screen’s resolution, then the image can either be downsized to fit (which makes it appear more detailed in general), or it will stretch off the screen.
Vice versa, using a low resolution image on a high resolution display can cause pixelation (where you can see the individual pixels that make up the image). It’s better to take a big image and zoom out (downscale) than it is to take a small image and enlarge it (upscale). This is why high resolution cameras are desired, especially for printing or publication purposes.
Resolution (Optical) – The smallest detail that the microscope’s optics are capable of visualizing for you. This is typically measured by the numerical aperture (NA) rating of an objective.
S
Scanning Electron Microscope (SEM) – A device in which the specimen is examined point by point directly in a moving electron beam, and electrons reflected by the specimen are used to form a magnified, three-dimensional image on a television screen. The samples must be coated in a metallic conductive and reflective surface in order to be imaged with a scanning electron microscope.
Stereo Microscope – A type of microscope that has two independent paths of light, and a pair of objectives for each magnification power offered (or moving lenses if a zooming unit). These are offset from each other (focused at slightly different points), which allows for a 3D image to be displayed in the microscope. This allows one to see a degree of depth in their sample. Commonly used for larger objects, like bugs, rocks, coins, stamps, and circuit boards.
T
Translucent Samples – Subject material to be viewed that light can pass through. This is the type of sample compound microscopes are commonly used to view, like tap or pond water.
Transmitted Light – Light that is sent up from the bottom of the microscope, through the sample, and into the eyepieces. Used for translucent samples, primarily in slides or petri dishes.
Trinocular – This refers to the number of eyepieces available on a given microscope. It uses the prefix “tri” for “three” with the suffix “ocular” for “being of the eye,” meaning it has three ocular tubes to view with. Since we have at max two eyes, the third port is commonly used to insert a digital camera, or a third eyepiece for another individual to view through.
U
V
W
Working Distance – This is the distance between the lens and your sample, and also called focal distance. The more magnification used in a microscope, the less working distance is available, as you have to move your microscope objective closer to the sample to achieve a focused image. Likewise, the less magnification used, the longer your working distance becomes. This is critical for stereo microscopes where the user needs to operate with tools under the microscope, or for compound microscope users that wish to use large glass medium like petri dishes or beakers.
X
Y
Z
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