lab_02_microscope

Lab_02_microscope - Miramar College Biology 205 Microbiology Lab Exercise 2 The Microscope Background A microscope is used to look at things that

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Lab Exercise 2: The Microscope Page 1 of 6 Miramar College Biology 205 Microbiology Lab Exercise 2: The Microscope Background A microscope is used to look at things that are too small to be resolved , or seen, with the naked eye. As such, the microscope is one of the most important tools to microbiologists. In this laboratory, we utilize a compound optical microscope . Compound, because it has more than one lens and optical because light is what transmits the image to your eye. Although it is difficult to pinpoint the exact origin of the microscope, Robert Hooke and Anton van Leeuwenhoek are both credited with bringing the microscope to the field of biology (Figure 1). Figure 1: Photograph of a microscope made in the style of Anton van Leeuwenhoek. Today’s microscopes are a far cry from those invented in the 17 th century and a typical student compound optical microscope will have the capability of magnifying an object up to 1000 times (1000×) its size. Even with all of the modern advancements, the principles of microscopy remain the same. The total magnification of a given object is the product of the ocular lens power and the objective lens power. The Nikon Alphaphot-2 has 10× oculars and four different objective lenses. If an object is viewed using the 4× objective, the object is actually seen at 40× its actual size. This principal can be extrapolated for the remaining three objectives. Resolving power is also an important consideration. Resolution is the ability to distinguish two closely spaced objects as distinct and separate. When magnification exceeds resolving power, the object in view is blurry. The resolution of the human eye is approximately 300μm but the resolving power of your microscope is closer to 0.2μm when the 100× objective is used. Two more things to consider when viewing an object with your microscope are field of view (FOV) and depth of view (DOV) , both of which have an inverse relationship to magnification. Field of view refers to the amount of an object that can be seen under the microscope. Field of view decreases as magnification increases. For instance, your FOV at 100× (using the 10× objective and looking through 10× oculars) is 2.5 times smaller than the FOV of the 4× objective lens ( i.e. 100/40 = 2.5). Additionally, depth of view- which refers to the thickness of the plane in focus- changes similarly with a change in magnification. As the magnification is increased, the DOV decreases and you are able to see a thinner slice of the microscope slide-specimen under view. This is one reason why even a parfocal microscope must be fine focused when the objective is changed. It is also the reason that a slide placed on the microscope stage upside down will be visible under low magnification but impossible to see under higher magnification. Learning to estimate the size of objects being viewed under the microscope is an important tool in the microbiological
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This note was uploaded on 12/23/2009 for the course BIO 205 taught by Professor Murphy during the Fall '09 term at Miramar College.

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Lab_02_microscope - Miramar College Biology 205 Microbiology Lab Exercise 2 The Microscope Background A microscope is used to look at things that

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