THE MICROSCOPE

1
THE MICROSCOPE

• Lab 2

2
Objetives

• Be able to define the following terms.
• a.- coarse adjustment knob i.- field of
  view
• b.- fine adjustment knob j.- depth
  of field
• c.- stage
  k.- resolving power
• d.- iris diaphragm l.-
  slide
• e.- ocular lens m.-
  coverslip
• f.- objective lens n.-
  dry mount
• g.- parfocal capability o.-
  wet mount.

3

• Be able to construct a wet mount and focus on the
  specimen in the center of the field of view,
  using high power.
• Be able to estimate the size of an object under
  low power or high power, given the dimensions of
  the fields of view.
• Be able to determine the system magnification of
  a set of lenses, given the magnification of each
  separate lens.
• Be able to convert micrometers to millimeters and
  millimeters to micrometers.
• Be able to describe the function of various parts
  of a microscope.

4
Magnification

• The compound microscope combines the magnifying
  powers of the ocular lens with the magnifying
  powers of the objective lens.
• The magnifying power of each lens is marked on
  its tubular housing.
• Simply multiply the magnification value that is
  marked on the ocular lens housing times the value
  marked on the objective lens housing to determine
  how many times your specimen is enlarged.

5

• Microscopes often have two additional objective
  lenses, namely a high-power lens and an
  oil-immersion lens. The latter will be the
  longest and have the highest magnification. The
  oil-immersion lens will be used only after you
  have had special training in oil-immersion
  technique.

6
THE MICROSCOPE
7

• Microscope Part
  Function
• 1- Ocular lens (eyepiece) Lens
  through which you view magnified
  specimen
• 2- Revolving nosepiece Movable
  mount for selecting objective lens
  best suited for
• extent magnification desired.
• 3- Objective lens.
  Lens on revolving nosepiece which
  accomplishes the initial
• magnification of the specimen.
• 4- Stage
  Flat work surface upon which
  the slide is placed. Some
  microscopes have a mechanical
• stage which is used for precise
• movement of a slide via control
• knobs geared to the stage.
• 5- Disc diaphragm
  Regulates the intensity of light
  passing through the stage
  aperture and specimen.

8

• 6- Light Source A lamp
  beneath the disc diaphragm, provides a
  constant light source.
• 7- Stage clips Fit over
  ends of a slide to hold it in place. A
  microscope having a mechanical stage has
  a Lever which is opened laterally (never
  lifted)To secure the side surfaces
  of a slide.
• 8- Coarse adjustment knob Gives gross movement
  of the nosepiece for initial focus
  effort.
• 9- Fine adjustment knob Gives refined
  movement of the nosepiece for finishing
  focus.
• 10- Base Supports
  the microscope.

9
Resolving Power

• Resolving power is a measure of lens quality.
  Quality lenses have a high resolving power, which
  is the capacity to deliver a clear image in fine
  detail. If a lens has a high magnifying power but
  a low resolving power it is of little value.
  Although the image may be large, it will not be
  clear enough to show fine detail.

10

• Another factor that reduces resolving power is
  the cleanliness of the lenses. Dirt, water, or
  oil on the lens may scatter light and reduce the
  effective resolving power of th microscope.
  Therefore, lenses should always be kept clean.
  Use only the recommended paper to clean the
  highly polished lens surfaces.

11
Viewing and Focusing

• Before you attempt to view any specimen through
  the microscope today, you must learn the correct
  use of the coarse adjustment knob.
• First, click the low-power objective lens into
  position directly over the stage aperture. Next,
  watch the stage and objective lens from alongside
  (not through) the microscope and turn the coarse
  adjustment knob to close the gap between the lens
  and stage to a minimum.

12

• Based upon your observation of microscope
  movements, and without having a specimen slide on
  your stage yet, determine the direction of coarse
  adjustment knob rotation you should use to move
  objective away from slide.

13
PROCEDURES

• 1- Turn on the illuminator using the on/off
  switch
• 2- Turn the nosepiece to bring the 4X objective
  (scanner) into position
• 3- Raise the stage into its highest position
• 4- Place a slide of the letter e in the slide
  clamp on the stage
• 5- Turn the coarse adjustment knob to bring the
  e into focus
• 6- Measure the field (the brightly lighted circle
  that you see when you look through the ocular
  lens)
• 7- Center the e in your field of view and then
  rotate the nosepiece to 10X
• 8- Use the fine adjustment knob to focus until
  the image is sharp. Draw the image. Do not use
  the coarse adjustment
• 10- Rotate the nosepiece until the 40X. Draw the
  image

14
Measurements

• At times it can be very useful to know the
  size of a specimen. This can be accomplished by
  using the field of view as a scale and simply
  visualizing it as divisible into ten equal parts.
  All that remains is to determine the actual
  length of each 0.1 of the field of view.
• Use the following formula to calculate the
  diameter of the high power field of view
• c
  a x b ___________
• 
  d

15
CARES OF THE MICROSCOPE

• When moving the microscope, carry it with 2 hands
  (one hand to grip the arm and the other under
  the base
• Lenses have to be clean with lens paper (to keep
  them free of oil and dust).
• Do not use the coarse adjustment when focusing
  with the higher power objectives