Microbiology Lab 1: Brightfield Microscopy

Brightfield Micrscope

A microscope that allows light rays to pass directly to the eye

Who discovered microorganisms

Anton van Leeuwenhoek

What did people, prior to the development of the microscope, believed caused epidemic diseases

“Bad air”

Who designed the first microscope

Anton van Leeuwenhoek

What adjusts the light of a microscope

An intensity control knob or slider

Where is the intensity control knob of microscopes usually found

Near the on/off switch

What are the three lens systems that compound micrscopes have

Oculars, objectives, and a condenser

Ocular

Also known as the eyepiece; located at the top of microscopes. They consist of two or more internal lenses

What is the magnification of the eyepiece of a microscope

Usually 10x

Nosepiece

The rotatable portion of a microscope

Objectives

A seriesof lenses attached to the nosepiece

What magnifications do the objectives of a microscope have

10X, 40X, 100X, and 4X for scanning

How is the total magnification of a compound microscope determined

By multiplying the power of the ocular lens times the power of the objective lens used

Condenser

Located under the stage. Collects and direct the light from the light source to the slide being studied.

What does the condenser of a compound microscope do to the magnification of the scope

Nothing

What moves the condenser up or down

A knob under the stage called the diaphragm

Coarse adjustment knob

Moves the stage of a micrscope up and down considerably

How does one change the interocular distance of an eyepiece

By simply pulling apart or pushing together the oculars

Diopter adjustments

Changing the distance between the oculars by making changes for right and left eye differences

Resolving power

The ability of a lens to completely separate two objects in a microscopic field

Resolving power equation

d = 0.5lambda/NA

d in the resolving power equation

The limit of resolution 7or the distance between two objects

Numerical aperture

A mathematical expression that describes how the condenser lens concentrates and focuses the light rays from the light source

When is numerical aperture maximized

When the light rays are focused into a cone of light that passes through the specimen into the objective lens

What results in a lower numerical aperture value

The greater the loss of refracted light, the lower the numerical aperture

What is the limit of resolution of most light microscopes

0.2 micrometers

What are some things that can be done to maximize the resolving power of a lens system

A blue light filter, high position condenser, not closing the diaphragm too much, and immersion oil for the 100X object lense

What kind of tissues should be used to clean lenses

Lint-free, optically safe tissues

How to determine if the eyepiece is dirty or not

Rotate the eyepiece as you look through the microscope. If objects seen through the microscope move with the rotation, this is evidence of dirt and artifacts on the oculars

What is the purpose of starting with a low-power objective when using a microscope

In order to explore the slide to look for the object you are planning to study

Parfocal

Images will remain in focus even with changing objectives

Parcentral

Image will remain centered even with changing objectives

Working distance

The distance between the microscope slide and the lens

What happens to working distance as the magnification of a microscope increase

Working distance decreases