Here are the most common metric prefixes we will use:

• kilo ( k )= 10³
• centi ( c ) = 10^-2
• milli ( m )= 10^-3
• micro ( μ ) = 10^-6
• nano ( n ) = 10^-9

You should know how to do conversions between these and to express them in scientific notation. Here's a site where you can convert between metric and english systems.

Microscopy

We are using light microscopes. There are a number of kinds, ours is bright-field. The light simply goes through the sample into the the lenses and we detect the sample by how much light is absorbed. This often requires staining as many cells don't absorb much light on their own. Fancier microscopes, such as phase contrast, use special methods to produce contrast so you can look at living cells. The resolution of a microscope is limited by the wavelength of the light. Light microscopes are limited to about 1500X because of the size of visible light. Electron microscopes (EM) can achieve much higher magnification (as much as 50,000,000X) because electrons have a much smaller wavelength (thank you Einstein).Samples for transmission EM must be stained and sliced extremely thin so the electrons can pass through and not be blurry. Scanning EM looks at electrons bouncing of a sample coated with metal to produce really cool 3D images. Here's a site with a bunch of colorized scanning EM pictures. All you care to know (and more) can be found at wikipedia's microscope article.

Steps for handling a microscope:

• Carry it with two hands, by the base and the handle (or neck) in the back. Not by the stage or lenses!
• The stage should be all the way down. The scanning objective (shortest one) should be in place. Plug it in and set the light to a reasonable setting.
• You may clean lenses at any time using a Kimwipe and lens cleaning solution, nothing else!
• Place the slide on the stage and clip it into place. The slide does NOT go under the clip! It's held in place by spring tension.
• Raise the stage all the way up. Since you are using the shortest (scanning 4X) objective, it cannot hit the slide.
• You can eyeball the sample to see if it is in the light and likely to be visible. Center it using the stage control.
• Slowly lower the stage using the coarse focus till the sample is in focus.
• You may change to the low power objective (10X). You should be able to achieve focus using the fine focus knob.
• You may change to the high power objective (40X). Use only the fine focus knob, you do not want to crash the objective into the slide!
• Between samples and before you put it away, make sure the light is off, the stage all the way down, and scanning objective in place.
• Put it away.

The parts of a microscope you should know.

• Ocular lenses
• Objective lenses
• Stage
• Substage light
• Condenser lens (focus light on sample)
• Stage
• Stage Controls
• Coarse and fine adjustment knobs
• Iris (can increase contrast at high magnification)
• Light Control

Parfocal - This means that once you have achieved focus with the scanning objective, rotating to a higher power objective will also be in focus (or nearly so).

Total Magnificaton - This is the power of the objective lens times the power of the ocular lens.Our oculars are 10X so the total magnification is simply 10 times whatever the objective is (4X, 10X, 40X = 40X, 100X, and 400X). We do not have the highest power objective installed on our microscopes. Brenda has the 100X (1000X total) oil immersion lenses in a drawer somewhere. These require a drop of oil to be placed between the sample and objective making them both messy and easy to damage.

Inversion - Images seen in microscopes are reversed both left to right and up to down. When you move the stage to the right, the image as seen through the lens appears to be moving toward the left. Oddly enough, our "e" slide already has it inverted so we see it as normal in the microsope!

Diameter of Field - This is simply the width of the visible area in a microscopic field. The lower the power, the bigger this field is. That's one reason you start with the scanning power. It's easier to find the sample! The relation between the diameter of field for the different powers is simply the ratio of their powers. If scanning power (40X) had an 8 mm field of view then low power (100X) would have 8mm X 40/100 or 3.2mm. High power would have 8mm X 40/400 or 0.8mm.

Depth of field - This is the depth (vertical distance) of a sample that is in focus. This also gets smaller as you go to higher powers (another reason to always start with the scanning objective). You can tell the order of the threads slide on high power (by slowly changing the focus) but not on scanning power.

From PSTCC's Official Practical Review

• What is meant by "compound light microscope"?
• Know the parts and the function of the parts of the compound light microscope.
• Know the steps for focusing a sample at the lowest power.
• What is meant by parfocal?
• Be able to calculate the total magnification of a scope with any objective.
• Does low power or high power have a larger field of view? How did we calculate the field of view of our scopes?
• How do you prepare a wet mount of cheek cells?
• What is meant by "depth of focus"?
• What is meant by "inversion" related to microscope use?