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 the width of an average bacterium, or a mitochondrion human red blood cells are seven micrometers across average human cells are in the range of 10 or 15 micrometers in diameter. 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; and he also showed exactly what was needed to achieve that. Phase contrast microscopy (and the even better version called DIC =Differential Interference Contrast microscopy) create contrasts, even in transparent cells, based on local differences in refractive index = how much materials slow light down. Fluorescence microscopy is one of many specialized methods of light microscopy. Fluorescent dyes are bound to certain chemicals, etc. A new kind of fluorescent microscope is called a confocal microscope. 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. There are also acoustic microscopes that use sound instead of light. (high frequency sound; because resolution is limited by wave-length!) These "see" how stiff cells are at different locations. Dear Dr. Harris, (E-mail advertisement received Thursday) If you are looking for a system to document and analyze fluorescent or bright light images you should consider our new Image-2 System. The system includes scientific quality color CCD camera with on-chip integration for low light or fluorescence and full-featured image analysis software for both Mac and PC. The system is suitable for such applications as multi-spectral FISH imaging and capturing the finest color images for publication. The camera features C-mount for easy attachment to the microscope or to lenses and optical couplers. The system's video output can be used to display live video on an external monitor or to send enhanced and annotated images to a color video printer. Comes installed on PC or Mac ($7,395). The system without the computer costs only $4,800. Fluorescent microscopes, motorized stages and auto focus attachments are also available. (They mean a "Fluorescence microscope" a "fluorescent microscope" would be a microscope that glows in the dark) Visit http://biosciencetools.com/image.htm for more details and specifications. Sincerely, http://biosciencetools.com CB Consulting, Inc. 77 Mason Ter. #12 Brookline, MA 02446 FAX/phone: (877)-853-9755 Electron microscopes ("transmission EM") use electron beams instead of light use magnetic and electric fields instead of lenses have 100 or 1000 times better resolution because the effective wave-length of electron beams is less than 1000th that of light. Disadvantages: vacuum; can only see dead things contrast by "staining" with lead, uranium etc. Scanning electron microscopes: specimens must first be coated with metal. often used for magnifications no bigger than light microscopes, but has a very big "depth of field" 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? What about the size of an average human cell? How wide is an average bacterium? How wide is a mitochondrion in a cell? 6) What are the special advantages of ? phase contrast microscopy? ? video microscopy? ? fluorescence microscopy? ? acoustic microscopy? *7) DVDs hold twice as much information per area than CDs, because DVD players use blue lasers and CD players use red lasers. Figure out how is related to the resolution of microscopes. 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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