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Brightfield Microscope
Brightfield Microscopy
51
Microbiology
Undergraduate 2
10/22/2011

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Cards

Term
What is a Brightfield microscope?
Definition
A microscope that allows light rays to pass directly to the eye without being deflected by an intervening opaque plate in the condenser.
Term
What is the framework of a Brightfield Microscope made of?
Definition
Arm & Base
Term
What is the stage of a Brightfield Microscope?
Definition
The horizontal platform that supports the microscope slide.
Term
What is the stage adjustment of a Brightfield Microscope?
Definition
A clamping device used for holding and moving the slide around on the stage.
Term
What does the light intensity control do?
Definition
It varies the intensity of light.
Term
What does a neutral density filter do?
Definition
It reduces the intensity of light below the lower limit allowed by the voltage control.
Term
How many lens systems do compound microscopes have?
Definition
3
Term
What are the lens systems of a compound microscope?
Definition
Oculars, objectives and condenser.
Term
What is the ocular also called?
Definition
Eyepiece
Term
What does the ocular consist of?
Definition
2 or more internal lenses
Term
What is the magnification of the ocular?
Definition
Usually, 10x
Term
How many objectives are there in a compound microscope?
Definition
Usually, 3 or more
Term
Where are the objectives located?
Definition
Attached to a rotable nosepiece.
Term
What are the magnifications of objectives?
Definition

10x (low power)

40x (high-dry)

100x (oil immersion)

Term
How is the TOTAL magnification of a microscope calculated?
Definition

"power of ocular" x "power of objective"

 

Eg: 10 x 100 = 1000

(the object is magnified 1000 times its actual size)

Term
Where is the condenser located?
Definition
Under the stage.
Term
What does the condenser do?
Definition
It collects and threads the light from the lamp to the slide.
Term
What's the difference between the condenser and the other two types of lenses?
Definition
It does not affect the magnifying power of the compound microscope.
Term
How can the condenser be moved?
Definition

Up

Down

Term
What does the diaphragm do?
Definition
It regulates the amount of light that reaches the slide.
Term
Which are the focusing knobs?
Definition

Course adjustment

Fine adjustment

Term
What are the focus knobs used for?
Definition
Used for bringing objects into focus.
Term
How to make diopter adjustments?
Definition

Focus with the right eye only

Turn the diopter adjustment ring until sharp imagine is seen with the left eye as well.

Term
What is the resolving power?
Definition

It is an intrinsic property of lenses that sets the limit for magnification.

 

Also, it is a lens' ability to completely separate two objects in a microscope field.

Term
What is the formula for the resolving power?
Definition
d = 0.5 (lambda)/NA
Term
What is NA - Numerical Aperture?
Definition
It is a mathematical expression that describes how the condenser lens concentrates and focuses the light rays from the light source.
Term
When is NA maximized?
Definition
When the light rays are focused into a cone of light that then passes through the specimen into the objective lens.
Term
What lowers NA?
Definition
Loss of refracted light
Term
What is the limit of resolution for any light microscope?
Definition
0.2 micrometers
Term
How large are bacterial cells?
Definition
About 1 micrometer.
Term
Why use a blue filter over the light source?
Definition
Because the shorter wavelength of the resulting light will provide max resolution.
Term
What are some other things one could do to max resolution?
Definition

1. condenser: highest position

2. diaphragm: not stopped down too much

3. use immersion oil (100x)

Term
What is special about immersion oil?
Definition
Has the same refractive index as glass.
Term
What does the immersion oil do?
Definition
It forms a continuous lens system that limits the loss of light due to refraction.
Term
Are magnification and resolution directly proportional?
Definition
Yes!
Term
Could one achieve greater magnification by adding a stronger ocular lens?
Definition
No!
Term
What should one use to clean the lenses?
Definition

1. lint-free, optically safe tissues

2. solvents (green soap and warm water, xylene, alcohol and acetone - used sparingly)

Term
What should not be touched in high-dry examination?
Definition
The coarse adjustment knob!
Term
What does parfocal mean?
Definition
The image will remain in focus when changing from a lower-power lens to a higher-power lens).
Term
What should one do when using the oil immersion technique?
Definition

1. Use oil immersion oil

2. Open the diaphragm as much as possible

3. Keep condenser at highest point

4. Use blue or green filters

Term
Magnification increases as the working distance of the lens ...
Definition
decreases.
Term
Describe the position of your hands when carrying the microscope to and from your laboratory bench.
Definition

One hand - under the base (to support its weight)

Other hand - on the arm (for balance)

Term
What is the limit of resolution of the unaided human eye?
Definition
0.2 mm
Term
What 2 adjustments can be made to the condenser?
Definition

1. Condenser height

2. Disphragm

Term
What effect do adjustments to the condenser have on the image?
Definition
Illumination is increased (when condenser is raised and disphragm is opened)
Term
Why are condenser adjustments generally preferred over the use of the light intensity control?
Definition
Condenser adjustments will increase illumination without affecting the bulb life.
Term
Why is it necessary to use oil in conjuction with the oil immersion lens and not with the other objetives?
Definition
Because the small working distance does not allow enough light to enter the lens. The oil directs more light into the lens.
Term
The coarse and fine focus knobs adjust the distance between...
Definition
the stage and the objective lens.
Term
The most useful adjustment for increasing image contrast in low-power magnification is ...
Definition
closing down the diaphragm.
Term
What is the field of view?
Definition

Area viwed through ocular.

 

Decreases with increasing magnification

Term
Brightfield is beter used for ... cells.
Definition
STAINED
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