Section G

Question 1

compound microscope is composed of two lenses.

Answer 1

• a primary magnifying lens (ocular)-closest to the eyes and usually magnifies objects 10x their actual size
• a secondary lens system (objectives)-are a collection of lenses located in the nosepiece with different degree of magnification

Question 2

Base

Answer 2

Supports the microscope and contains the light source, held by one hand when carrying microscope

Question 3

Light Source

Answer 3

Located in the base.Provides illumination for the specimen, has a dimmer switch to control brightness

Question 4

Arm

Answer 4

Supports the stage and body tube, held by other hand when carrying microscope

Question 5

Condenser

Answer 5

Lens system below the stage (sub-stage) that focuses and concentrates light on the specimen . Has an adjustment knob, that raises and lowers the condenser to verify light delivery. Contains iris diaphragm.

Question 6

Iris Diaphragm

Answer 6

Adjustable opening like iris of eye, regulates amount of light (diameter of light beam) passing through the condenser. Controlled by a lever, that permits the best possible contrast when viewing a specimen.

Question 7

Course adjustment

Answer 7

Used to focus on the specimen. Rotating knob that rapidly brings the specimen into focus by raising /lowering the stage, used only with low power objective.

Question 8

Fine adjustment

Answer 8

Rotating knob that slowly brings the specimen into sharp focus,used for critical focusing at low power and for all focusing at high power magnification.

Question 9

Condenser control

Answer 9

Rotating knob that moves the condenser lens system up and down

• The condenser is very important in image formation.
• Like a microscope objective, a condenser has a numerical aperture and it should equal or better that of the highest magnification objective being used.

Question 10

Mechanical stage

Answer 10

The platform that slides are placed on while being viewed. Platform has an opening in the center to allows light from lenses to pass through it as well as the specimen.
Usually has a spring clip to hold the slide in position for viewing.

Question 11

Vernier scales

Answer 11

Set of scales on X and Y-axis that allow for the location of a particular object on a slide.

Question 12

Stage control

Answer 12

Rotating knobs located under the stage that move the stage from left to right and back and forth.

Question 13

Objectives lenses

Answer 13

Glass lens nearest the stage, magnifies image of the specimen by amount shown on the side of the lens producing a real, inverted image.
Lens system:10X (scanning lens), 40X (low power/high dry lens), and 100X(high power/oil immersion lens)

• The objective lens magnifies the specimen to produce a REAL IMAGE that is projected to the ocular.

Question 14

Revolving nose piece

Answer 14

Rotating mechanism for objective lenses (usually 3-4) so they may be alternately positioned into the light path for different magnification.

Question 15

Body tube

Answer 15

Joins nosepiece to oculars, has mirrors to pass image from objective lens to oculars.

Question 16

Ocular

eye piece

Answer 16

One ot two glass lens closest to eye. Observations are made through the ocular(s).
An ocular lens has a magnification of 10X . (increases the size of the object by 10 times)
Magnifies real image from the objective lens, usually by producing a virtual, enlarged image.

Question 17

Diopter

Answer 17

Focusing ring located on the ocular lens, allows for sharp focusing withboth eyes.

Question 18

What is magnification

Answer 18

microscope is an instrument of magnification

• Magnification is the ability to increase the size of an image–not clarity
• Magnification uses lenses ( in the microscope the ocular lens and the objective lens)

Question 19

resolution of a microscope

Answer 19

ability to clearly determine two close objects as separate or as singular, distinguished entities.
• The shortest distance between two points on a specimen that can still be distinguished by the observer
• The microscope has a resolution of 0.2 um
• The human eye can resolve objects about 100um apart
• If the objects are closer than 0.2 um, they will appear fused as a single object or points will blur together, making it impossible to differentiate

• If two objects are 0.01 mm apart, we cannot detect them unless we magnify an image of them by 10X

Question 20

• Resolving power

Answer 20

is determined by the amount and physical properties of visisble light (wavelength spectrum of light ) entering the microscope.
• The more light delivered to the objectives the greater the resolution
• Blue light gives better resolution than yellow or red
• Blue filter used on microscope to “hold Back” longer wavelength of light

Question 21

NUMERICAL APERTURE

Answer 21

The numerical aperture of a microscope objective is a measure of its ability to resolve fine specimen detail.
The numerical aperture of a lens is dependent upon two parameters

• The angle of the incidence of light onto the lens
• The refractive index of the glass of which the lens is composed.
• The size of the objective lens aperture (opening) decreases with increasing magnification, allowing less light to enter the objectives

When using the microscope it may be necessary to increase the light intensity as the magnification gets higher.

Question 22

REFRACTIVE INDEX (R I)

Answer 22

ability of the microscope to both magnify and resolve (or allow small structures to be seen) depends on the refraction or bending of light
speed at which light passes through a medium of one density to another in a vacuum

Question 23

Refraction

Answer 23

bending of light as it passes from one medium to another

• Immersion oil which has the same refractive index as glass is used to replace the air. The slide and lens are joined by a layer of oil
• As the wavelength of light increases, the refractive index decreases.

Question 24

• Scanning power objective:

Answer 24

shortest objective. This lens magnifies objects four times actual size (4X).

Question 25

• Low power objective:

Answer 25

The next shortest objective. This lens magnifies objects ten times their actual size (10X). Also used for scanning

Ocular x Objective = 10 x 10X = 100 Total magnification

Question 26

• High-dry objective:

Answer 26

This is usually either the longest, or second longest objective. This lens typically magnifies objects forty times their actual size (40 X).

Question 27

• Oil immersion objective:

Answer 27

The oil immersion lens magnifies objects one hundred times (100X), and must be used with a drop of oil placed directly on the specimen and fills the space between the lens and specimen.

Question 28

Vernier Scales (Coordinates)

Answer 28

• The X coordinate is obtained using the scale at the top of the stage running from right to left
• The Y coordinate is obtained using the scale running from top to bottom along the side of the stage.
LEARN TO READ

Question 29

Daily and weekly maintenence

Answer 29

1. When not in use, keep the microscope protected with a plastic cover.
2. Unplug microscope and wash hands.
3. Accumulated dust in a microscope can deteriorate image quality. Keep all openings covered so that dust does not enter the microscope and settle on lenses, mirrors, and prisms.
4. Wipe the stage with a damp cloth and mild detergent, and clean off any immersion oil with ethanol or lens cleaner.
5. Carefully clean the objectives (see detailed description below).
6. Remove and clean any dust or immersion oil from the condenser and turret using dry Kimwipe. Weekly give immersion lens a through cleaning (see description below)
7. Remove the condenser top lens and clean it with lens paper and diluted methanol , if necessary.
8. Remove both eyepieces and clean their surfaces with a Kimwipe and lens cleaner.

Question 30

Objective Cleaning

Answer 30

3. A through cleaning of immersion objectives is necessary at least once peer week. Some cleaning agents can erode the anti-reflection coating over time.

 Remove the objective from the turret.
 Add a few drops of diluted methanol to lens tissue.
 Gently wipe the lens in a circular motion (only letting the tissue, not your fingers, come into contact with the lens element).
 Remove any excess methanol immediately with a dry piece of tissue – allowing ethanol to remain on the lens could erode the anti-reflection coating.
 For stubborn smears, place a drop of xylene or benzene on lens paper. Gently wipe the lens in a circular motion. Remove xylene or benzene with diluted methanol.
 Xylene or benzene is toxic, so wear PPE and use under a fume hood

Question 31

Köhler illumination

Answer 31

August Köhler of the Carl Zeiss corporation as a method of providing the optimum specimen illumination.

course adjustment knob to bring the stage and objective close together…bringing your object into focus. Watch the objective lens to make sure that the lens does not break the slide.

needs a high density illumination source, field diaphragm, condenser diaphragm, and collector and condenser lenses.