# Microscope Principles Study KEY Describe the function

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```					                           Microscope Principles Study Questions KEY

1.      Describe the function of the following components of the microscope, noting their location
on a microscope image and the microscope you are using: (textbook, page 1, 2, 6)
a.     Aperture (iris) diaphragm (open aperture diaphragm on your microscope to 1/3 open)
microscope component that regulates the angle of light presented to the
specimen. Located at the base of the condenser, changes the diameter of the
opening through which the source light rays must pass to enter the condenser

b.      Condenser, substage (move the condenser of your microscope to the lowest position)
microscope component that gathers and focuses the illumination light onto the
specimen for viewing; located beneath the stage

c.      Eyepiece (ocular)
microscope lens or system of lenses located closest to the viewer’s eye; produces
the secondary image magnification of the specimen

d.      Illumination system (light source) a tungsten or a tungsten-halogen lamp located
in the base of the microscope; provides microscope system with light, often
called source light, source rays

e.      Mechanical stage (adjust the stage to its lowest position using the coarse adjustment
knob)     microscope component that holds the microscope slide with the
specimen for viewing. Stage is adjustable, front to back, side to side, to enable
viewing of the entire specimen

f.      Objectives (place the low power (10X) objective into the light path)
the lens or system of lenses located closest to the specimen. The objective
produces the primary image magnification of the specimen

2.      Define the following terms as they relate to microscopy: (textbook, page 1, 2)
a.     Birefringent the ability of an object to refract light in two directions (also called
doubly refractile)

b.      Field of view (FOV) the circular field observed through a microscope’s ocular

c.      Numerical aperture a number that indicates the resolving power of a lens system.
Derived mathematically. The greater the NA, the greater is the resolving power
of the lens system. (Brunzel, p 2, 4)

d.      Resolution the ability of a lens to distinguish two points or objects as being
separate; ability of lens system to reveal fine detail (Brunzel, p 2, 3)

CLS 426 Urine and Body Fluid Analysis: Student Lab Rotation                                        1
Microscope Principles Study Questions KEY
3.      In the clinical laboratory, compound brightfield microscopes consist of a „two lens system‟.
Explain what this means and identify these components on the microscope you are using.
This means the microscope has an EYEPIECE (or ocular lens) and an OBJECTIVE
lens. The objective lens is located closest to the specimen and produces the primary
image magnification and directs this image to the second lens system called the eyepiece
or ocular lens. The eyepiece further magnifies the image. (Brunzel, p3)

4.      How is the total magnification of a specimen determined? Provide an example.
Total magnification of a specimen is the product of the ‘two lens system’: the objective
lens magnification times the eyepiece lens magnification. If the eyepiece lens
magnification is 10X and the objective lens magnification is 40X, then the total
magnification would be: (Brunzel, p 3)
(10) X (40) = 400X

5.      What is the purpose of the microscope lens system? (textbook, page 3)
The purpose of the lens system is to magnify an object for viewing with maximum
resolution

6.      Where is the correct position of the condenser? (textbook, page 6).
Always at its upper most stop, but is slightly lowered only with the Köhler illumination.

7.      When the aperture diaphragm is properly adjusted, what is the effect on the magnified image
we see? (textbook, page 6).
We achieve maximal resolution, contrast and definition of the specimen.

8.      What is the best way to reduce the brightness of the image field? List a common mistake
made when attempting to reduce the image field brightness and its effect on the image.
(textbook, page 6)
You should decrease the intensity of the light source (or place a neutral density filter
over the light source).
A common mistake is to adjust the aperture diaphragm to reduce the brightness. When
this is done, resolution of the image is decreased.

9.      Match the following objective magnification to the correct „power‟ terminology and clinical
use:

objective magnification          „power‟ terminology         clinical use

c-2      10X                   a. Oil immersion            1. Slide differential, gram stain

b-3      40X                   b. High power dry           2. Enumerating casts in urine

_a - 1   100X                   c. Low power dry            3. Enumerating RBC in urine

CLS 426 Urine and Body Fluid Analysis: Student Lab Rotation                                         2
Microscope Principles Study Questions KEY
10.     What is probably the greatest cause of harm to both the mechanical and optical components
of a microscope? Name at least three ways in which this hazard can be removed or avoided.
(textbook, page 9) Dust.
To remove dust:
a. use a grease-free brush (camel hair) or an air syringe
b. use a dust cover
c. place the microscope in a storage cabinet

11.     Immersion oil should be used only with the oil immersion lens. Explain how, when and why
the oil immersion lens should be cleaned. (textbook, page 9)
How: remove oil using dry lens paper
When: when finished using the objective and before putting the microscope away
Why: oil left on the surface of the lens can impair its optical performance

12.     Review the “do‟s and don‟ts” for routine use and maintenance of a microscope found on

13.     Briefly explain the key characteristics of the following types of microscopy:
(textbook, page 1,2)
a.      Brightfield microscopy type of microscopy that produces a magnified image that
appears dark against a white or bright background

b.      Phase-contrast microscopy type of microscopy in which variations in the
specimen’s refractive index are converted into variations in light intensity or
contrast. Areas of the specimen appear light to dark with haloes or varying
intensity related tot eh thickness of the component being viewed. Thin, flat
components produce less haloing and the best-detailed images. Phase-contrast
microscopy is ideal for viewing low-refractile elements and living cells

c.      Polarizing microscopy type of microscopy that illuminates the specimen with
polarized light. Polarizing microscopy is used to identify and classify
birefringent substances (ie substances that refract light in two directions) that
shine brilliantly against a dark background

d.      Fluorescence microscopy type of microscopy modified to visualize fluorescent
substances. Fluorescence microscopy uses two filters: one to select a specific
wavelength of illumination light (excitation filter) that is absorbed by the
specimen; and another filter (barrier filter) to transmit the different longer-
wavelength light that is emitted from the specimen to the eyepiece for viewing.
The fluorophore (natural or added) present in the specimen determines the
selection (wavelength) of these filters

CLS 426 Urine and Body Fluid Analysis: Student Lab Rotation                                     3
Microscope Principles Study Questions KEY

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