Light microscopes: magnification as compared with resolution "a thousand times...etc." one fifth of a micrometer a meter is 39 inches ( a little more than a yard=3 feet) a millimeter = 1/1000 meter; thickness of a pencil lead=the thickness of a microscope slide
a micrometer = thousandth of a millimeter: which is the same as a millionth of a meter
In the late 1800s, a German engineer showed mathematically that no light microscope can achieve a resolution better than about half the wave-length of the light being used;
Phase contrast microscopy
Fluorescence microscopy is one of many specialized methods of light microscopy. Fluorescent dyes are bound to certain chemicals, etc. From the 1970s until now, revolutionary improvements were made in light microscopy, mostly by using video cameras and applying fancy electronics to the video output. "Video Microscopy" UNC, especially this department's Ted Salmon were among the world leaders in these advances, although the 2 main scientists were Shinya Inoue of Penn and Woods Hole, and Bob Allen at Dartmouth. For example, specific proteins can be isolated chemically, then fluorescent chemicals can be attached to them, and the proteins injected back into cells! Where the proteins will go back to participating normally in cell activities, & followed by fluorescence microscopy. You can see things that are smaller than can be resolved!
Some optical methods allow you to "see" concentrations of calcium or other specific ions in cells, or to "see" where cells touch something.
Dear Dr. Harris, (E-mail advertisement received Thursday)Electron microscopes ("transmission EM")
use electron beams instead of light
Disadvantages: vacuum; can only see dead things
Scanning electron microscopes: Questions you should be able to answer: 1) What is the distinction between the resolving power of a microscope and its magnification? which is measured in distances? 2) Would it help to have a microscope magnify a million times, if its resolving power were no better than a microscope with a magnification of a thousand? 3) If you got dirt on the lens of a microscope, then would you expect this to reduce magnification or resolution? 4) Is there any inherent limit to the magnification of a light microscope? Is there any inherent limitation to its resolving power?
5) What is the width of a human red blood cell?
6) What are the special advantages of
? video microscopy? ? fluorescence microscopy? ? acoustic microscopy?
8) What do electron microscopes use instead of light? What do they use instead of glass lenses? 9) If a microscope used infra-red light, instead of visible light, then how would that alter its maximum resolution? *10) What properties of a cell would be "seen" by an infra-red microscope (if there were such a thing)? 11) If DNA and RNA absorb UV light, then how could you have a microscope that "sees" them? (If you make lenses out of quartz, then ultra-violet light will go through them.) 12) Why can't you look at living cells by electron microscopy? (2 reasons, actually)
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