Lab 1 - microscopes

Microscopes

ocular lens

The lens you look through; usually provides 10× magnification.

objective lens(es)

Provides the main magnification (e.g. 4×, 10×, 40×); combined with eyepiece magnification to give total magnification.

Mechanical stage

Flat surface the supports the slide or specimen over the hole that emits light from below

iris diaphragm

Controls the amount of light passing through the condenser onto the specimen.

Coarse focus knob

Moves the stage up and down quickly to bring the specimen into rough focus.

fine focus knob

Sharply focuses specimen by adjusting the distance between the specimen and objective lenses very precisely

Condenser

contains 2 lenses that focus light onto/through the specimen

difference between a compound and dissecting microscope

Compound: high magnification, low depth of field, used for thin transparent specimens;

Dissecting: low magnification, high depth of field, used for 3D or opaque specimens.

magnification

The process of enlarging an image compared to its actual size.

How do you calculate total magnification?

Eyepiece magnification × Objective magnification.

What is resolution?

The ability to distinguish two points as separate; determines image clarity.

What is depth of field?

The thickness of the specimen that remains in focus at one time; decreases with higher magnification.

Why is staining used in microscopy?

To increase contrast and make structures more visible.

What are the two main types of electron microscopes?

Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM).

What is the light source used in a light microscope?

Visible light.

What is the light source used in an electron microscope?

A beam of electrons.

What is the maximum resolution of a light microscope?

Around 200 nanometers (0.2 µm).

What is the maximum resolution of an electron microscope?

Around 0.2 nanometers.

What is the maximum magnification of a light microscope?

Up to about 400x (for us)

What is the maximum magnification of an electron microscope?

Up to about 300,000x

Can a light microscope view living specimens?

Yes.

Can an electron microscope view living specimens?

No, specimens must be dead.

Are images from light microscopes in color?

Yes.

Are images from electron microscopes in color?

No, they are grayscale (black and white).

Formula for calculating actual size of a specimen?

fraction of field occupied x field diameter

Formula for calculating speed of movement?

Distance moved ÷ Time taken.

If a cell moves 0.25 mm in 5 seconds, what is its speed?

0.25 ÷ 5 = 0.05 mm/s.

Explain the difference between resolution and magnification.

Magnification enlarges an image;

resolution determines how clearly two points can be distinguished.

Which microscope is better for viewing viruses?

An electron microscope, because viruses are much smaller than the resolution limit of light microscopes.

ways to improve resolution of light microscope

Blue light filter; immersion oil

ways to improve contrast of specimen

Staining; reducing light intensity