Light Microscope Parts and Functions

Created by pmrayfield 

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Ocular Lenses

These eyepieces further magnify the image formed by the objective lens. It does not improve resolution. They make up an adjustable binocular system. The magnification of the oculars is 10X. They are equipped with a pointer inside one of the lenses which makes it easier to point out specific structures or determine the real dimensions of the specimen you are observing.

Arm

Connects to the base and supports the microscope head. It is also used to carry the microscope.

Light Intensity knob

Light on/off switch and intensity knob. Controls the intensity of the light coming from the bulb.

Fine Focus Adjustment Knob

Controls precise focusing of the object. Only the fine adjustment knob should be used with the high magnification lenses - high power and the oil immersion objective lenses. Moving the fine adjustment knob also helps you to determine the third dimension (depth) of the specimen you are studying.

Coarse Focus Adjustment Knob

This is used for rapid (or coarse) focusing on the specimen when using the scanning objective lens and the low power lens. This course focusing knob is rotated until the specimen is roughly in focus and then left alone.

Mechanical Stage Adjustment Knobs

Two knobs that are located on the side of the stage and are used to move the slide around to locate your specimen. one knob moves the slide from side to side and the other moves the slide forward and backward. The mechanical stage permits precision movements of your slide , without you touching the slide yourself

Base

The bottom of the microscope used for support.

Lamp

Provides a steady light source and illumination of the specimen.

Condenser Lens

Connected to the iris diaphragm and located just under the stage. Contains a system of lenses that directs light from the lamp through the slide specimen.

Iris Diaphragm

Located on the condenser. The lever of the iris diaphragm is used to adjust the amount of light striking the specimen

Stage

Holds the slide to be observed. The center of the stage has an aperture or hole through which light passes to illuminate the specimen on the slide.

Stage Clips

They fix into position your slide on the stage.

Objective Lenses

The pattern of light formed by the specimen is focused into a real image by the objective lenses. When the proper illumination is provided the resolving power of a microscope depends on the quality of its objective lenses. There are four of them with magnifications of 4X, 10X, 40X, and 100X.

Revolving Nosepiece

The four objective lenses are mounted on this rotating turret or nosepiece. Rotating this turret allows you to switch between the objective lenses as you need them.

Resolution

Clarity of an image

Limit of Resolution

(resolving power). Actual measurement of how far apart two points must be for the microscope to view them as being separate.

Numerical Aperture

A Measure of a lens's ability to "capture" light coming from the specimen and use it to make the image.

Bright-field Microscopy

Produces an image made from light that is transmitted through a specimen. The specimen restricts light transmission and appears shadowy against a bright background - where light enters the microscope unimpeded. Because most biological specimens are transparent, the contrast between the specimen and the background can be improved with the application of stains to the specimen. The price of the improved contrast is that the staining process usually kills cells. This is especially true of bacterial-staining protocol.

Dark-field Microscopy

A special condenser is used so that only the light reflected off the specimen enters the objective. The appearance is of a brightly lit specimen against a dark background, and often with better resolution than that of the bright-field microscope.

Phase Contract Microscopy

Uses special optical components to exploit subtle differences in the refractive indices of water and cytoplasmic components to produce contrast. Light waves that are in phase reinforce one another, and their total intensity (because of the summed amplitudes) increases. Light waves that are out of phase by exactly 1/2 wavelength cancel each other and result in no intensity -darkness. Wavelengths that are out of phase by any amount will produce some degree of cancellation and result in brightness that is less than maximum but more than darkness. Thus, contrast is provided by differences in light intensity that result from differences in refractive indices in parts of the specimen that put light waves more or less out of phase. Specimen appears as various shades of darks against a bright background.

Fluorescence Microscopy

Uses a fluorescent dye that emits fluorescence when illuminated with ultra-violet radiation. In some cases, specimens posses naturally fluorescing chemicals and no dye is needed.

Parfocal Lenses

Lenses that are oriented in such a way that the specimen remains in focus as the objectives are rotated into place.

Depth of Field

The thickness of the specimen which can be seen when in focus. As you increase magnification the depth of field decreases.

Working Distance

The space between the front mount (bottom) of the objective lens and the top of the coverslip of the microscope slide is the working distance. The working distance decreases as the objective lens magnification increases.

Total Magnification

The total magnification of the lens system is the product of the magnification the ocular times the magnification of the objective lens being used (ocular X objective).

Name the 4 types of objective lens that are on the microscope and what is their objective magnification and total magnification?

1. Scanning Lens - 4X, 40X
2. Low Power Lens - 10X, 100X
3. High Power Lens - 40X, 400X
4. Oil Immersion - 100X, 1000K

Name Four Types of Light Microscopy

1. bright-field
2. dark-field
3. fluorescence
4. Phase Contrast Microscopy

What begins Image Formation?

It begins with light coming from an internal or an external light source.

What are the benefits of using Oil Immersion

Using Immersion oil between the specimen and the oil objection lens minimized the light loss as well as increased its numerical aperture and, in return, makes its limit of resolution smaller. The result is better resolution.

Light Microscopy

Used in conjunction with cytological stains is used to identify microbes from patient specimens or the environment.

What does "D" equal?

the minimum distance at which two points can be resolved - the actual limit of resolution.

Lens Paper

used for gently cleaning the condenser and objective lenses.

What is the Relationship between resolution and the limit of resolution (resolving power).

Resolution improves as the limit of resolution (resolving power is made smaller.

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