Lab Practical Microbiology 2 (3-1)

Front 1

What are the 4 types of light microscopes

Back 1

Bright-field Microscope
Dark-field Microscope
Phase contrast Microscope
Fluorescence Microscope

Front 2

Brightfield Microscope

Back 2

A microscope that allows light rays to pass through a
slide/specimen and then through various lenses to the eye. The lenses magnify
the object.

Front 3

Microscope Parts/functions

Back 3

1. Arm - all other parts are attached to it
2. Base - bottom
3. Stage - platform that holds the slide
4. Mechanical stage - device used to clamp slides to the stage
- allows the slide to be moved
5. Light source - provides illumination and is located in the base
6. Voltage control - varies the intensity of light; light will last longer if the voltage
control is kept on low

Front 4

Lens Systems

Back 4

Oculars => eyepieces (10X); has 2 or more lenses
Objective => 4 objectives; attached to the nosepiece for movement
1. Scanning (red band) - 4X
2. Low (yellow band) - 10X
3. High Dry (blue band) - 40X
4. Oil immersion (white band) - 100X

Front 5

Total Magnification

Back 5

magnification (ocular) X magnification(objective)

Front 6

Condenser

Back 6

under the stage; collects and directs the light; concentrates the light
for uniform illumination

Front 7

diaphragm

Back 7

part of the condenser that controls the amount of light coming through

Front 8

Focusing Knobs

Back 8

a. Coarse adjustment - major focus adjustment; use with low objectives (4X and
10X); moves the stage up and down
b. Fine adjustment - minor focus adjustment; use to do the final focusing of an
object

Front 9

Ocular Adjustment

Back 9

Ocular adjustment - want to see one image
- pull apart or push together the oculars
- Diopter adjustment ring - focus 1st with right eye then use ring to focus the left

Front 10

Resolution

Back 10

The ability to distinguish two adjacent points as separate objects based upon
resolving power

Front 11

Resolution is a function of what three things?

Back 11

-1. Numerical aperature
-2. Wavelength of light
-3. Design of condenser

Front 12

The optimum resolution of the best microscope with the oil immersion lens is?

Back 12

2 micrometers

Front 13

4 ways to increase resolution

Back 13

1. A blue or green filter should be in place - decreases the wavelength => increase
resolution
2. The condenser should be at its highest position which allows the maximum amount of
light to enter the objective.
3. The diaphragm should be opened up a little => less contrast but higher numerical
aperature
4. Immersion oil should be used between the slide and the 100X objective

Front 14

Numerical Aperature

Back 14

the measure of a lens’ ability to capture light coming from a
specimen and use it to make the image; increases with the use of oil and the higher objectives

Front 15

Limit of Resolution

Back 15

D = Wavelength / N A condenser + N A of objective lens

Front 16

Parfocalization

Back 16

the object should stay in focus when moving between
objectives

Front 17

Phase Contrast vs. Bright Field Microscopy

Back 17

- usually organelles and cells are transparent and difficult to differentiate without staining
- staining kills the cells so you don’t see living cell just artifacts
- phase-contrast allows one to view living transparent organisms using phase (wavelength
shifts) principles of light to produce bright objects in a dark background (like a negative of a
photograph).