02

Dissecting Microscope

A B

Carrying a Microscope

• Return the lowest power objective in place

• Wrap the cord around the base

• Return dustcover

Storing The Microscope

 

• Use lens paper on all glass parts of the microscope.

Cleaning the Microscope

Dissecting Microscope & Parts

Free standing illuminator

Pond Water Sample

Paramecium

Euglenia

Volvox

Clamydomonas

SpirogyraRotifer Daphnia

Prepare wet mount for dissecting scope• Pond water

Look at specimen under high power and draw what you see.

Use proper clean-up technique

Activity

Phase Contrast Microscope

Muscle tissue Downy mildew of grape

• Imperfections in glass• Peaks and troughs

don’t line up• These waves are in

different phases• PCM used to transform

phase differences into intensity differences, thus increasing contrast

Understanding Phase Contrast Microscopy

light

glass

light

waves

Destructive interference(Dark phase)

Constructive interference (Light phase)

Understanding Phase Contrast Microscopy

Dark FieldBright Field

Phase contrast

Comparison of Light Microscopy

Course adjustment knob

Fine adjustment knob

Y-axis knob

X-axis knob

Specimen holder

ocular

objective

Light intensity lever

Light intensity preset button

stage

Revolving nose piece

Aperture iris diaphragm ring condenser

 

• Use lens paper on all glass parts of the microscope.

• Clean oil immersion lens with chemicals provided by your instructor

Cleaning the Microscope

Using the microscope

• Always observe using the LOWEST POWER objective first.

• Focus using the COARSE ADJUSTMENT KNOB to bring the object into focus. Bring the object into sharp focus by using the fine adjustment knob.

• Focus, and then move to a higher power objective, if needed.

• Use only the FINE ADJUSTMENT KNOB when using the HIGHEST (longest) POWER OBJECTIVE.

• Keep both eyes open to reduce eyestrain. • Determine total magnification of the object by

multiplying the power of the ocular (10x) the power by the power of the objective.

Preparing a slide

• Using a pipet or dropper, add a drop of water or another solvent to a clean microscope slide. Then, place the specimen in the water.

• Place the edge of a coverslip on the slide so that it touches the edge of the water.

• Slowly lower the coverslip to prevent the formation of air bubbles.

The effects of immersion oil on resolution

40x 100x

Oil Immersion Lens

base

ocular

objective

Illumination intensity

stage

Nose piece

Specimen holder

Course adjustment

X-axis knob

Condenser

Iris diaphragm(aperture diaphragm ring)

Fine adjustment

y-axis knob

For Light Microscope use set to 0

Animal Cell

Plant Cell

Prepare wet mount• Cheek cell• Elodea cell• Onion cell• Bacterial cells in yogurt

Look at specimen under high power and draw what you see.

Use proper clean-up technique

Activity

Cheek Cell

Elodea

Epidermal Onion Cell

Dispose Biological material

Dispose Sharps

Clean Up

Microscope Parts Quiz

Microscope Quiz

1.    

1. Which objective uses oil?2. If your ocular is 10x and your

objective is 40x what is the total magnification of your image?

3. Why do you need a cover slip and how do you avoid an air bubble?

4. What is the difference between a light microscope and a dissecting microscope?

• When looking through the ocular you will see 2 rings

• The may or may not be concentric.• By turning the centering adjustment

screws o the condenser, you align the rings so they become concentric

Aligning rings

• Brightfield –absorptionLight is transmitted through the sample. Only useful

for specimens that can be contrasted via dyes. Very little contrast in unstained specimens.

• Darkfield -scatteringThe illuminating rays of light are directed from the

side so that only scattered light enters the microscope lenses, consequently the cell appears as an illuminated object against the view. 

• Phase Contrast- phase interferenceIncident light [Io] is out of phase with transmitted

light [I] and when the phases of the light are synchronized by an interference lens, a new image with greater contrast is seen

Dark-Field Microscopy• Modified condenser

contains disc in center• Only light refracted by

specimen can enter objective.

• Objects surrounded by halo.

• Advantage can see smaller objects like spirochetes, internal structures highlighted.

• Disadvantage objects look bigger than they actually are.

Phase Contrast Microscopy

• Light passes through annular diaphram.

• Causes light waves to become “in phase” or synchronized.

• Advantage can highlight internal cell structures and details.

• Disadvantage - none.