Microscopy : microscope Microscopy : Investigation by means of a microscope

JEM-3100F Transmission Electron Microscope (2006) …but there are many different kinds of microscopes!

Types of Microscopes We will use: Compound Light Microscope Discovery Scope (Simple Compound)

eyepiece/ ocular body tube arm Fine adjustment knob stage high power objective Coarse adjustment knob light low power objective Stage clips iris diaphragm base Revolving nosepiece stop screw Compound Light Microscope

Let’s Practice

MagnificationMagnification – how much an image is enlarged under a microscope (100X means object appears 100 times larger than it actually is) Field of ViewField of View – area that is visible through the microscope Light IntensityLight Intensity – how bright the light that reaches your eye is Microscope Definitions

As magnification increases, field of view decreases.

Depth of Field Depth of Field – the depth into a 3-D specimen that remains in focus at one time Resolution Resolution – the amount of detail you can see in an image (the ability to distinguish between two objects as separate) Total magnification Total magnification = ocular magnification x objective magnification

Types of Microscopes cont… There are other types of microscopes that scientists use to investigate things we can’t see with our eyes: Scanning Electron Microscope (SEM) Transmission Electron Microscope (TEM) Scanning Tunneling Microscope (STM) Press me!

Transmission Electron Microscope (TEM) Thin slice of specimen Specimen stained with metal ions Specimen placed in a vacuum chamber (dead) Electrons that pass through specimen are what create image 2-D image that is black & white (color can be added later)

Scanning Electron Microscope (SEM) Specimen doesn’t have to be sliced! Specimen stained with metal (gold) Specimen placed in a vacuum chamber (dead) Electrons that bounce off the specimen are what create the image 3-D image that is black & white (color can be added later)

Scanning Tunneling Microscope (STM) Uses a needle-like probe (one or two atoms) 3-D image Can show details as small as a single atom Two methods: – The tip follows a specific current; moving up and down to stay at that current – The tip stays a certain distance from the surface; the changes in current show movement up and down Want to know more?

The scale of specimens that can be seen with the naked eye, with the compound light microscope and with electron microscopes Press me!

CALCULATING FIELD OF VIEW

Practice

Place a piece of metric ruler on the stage so that it covers half of the stage opening. Start with low power (100X). Focus on the edge of the ruler. It should look something like the image below.

Align one mark to the left side of the field of view. Make sure the ruler crosses across the center of the field of view. Estimate!

Convert your estimation from millimeters (mm) to micrometers (µm) by multiplying by mm 2 mm 4.5 mm

Field of view under high power cannot be directly measured. We can find it indirectly, though. – Remember: Field of view decreases as magnification increases. high power field diameterlow power magnification = low power field diameterhigh power magnification