2 revolving nose piece the objective lenses are

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Unformatted text preview: t shown). This screw should remain tightened at all times and not used for changing the position of the eyepiece tube. 2. Revolving Nose Piece. The objective lenses are threaded into this structure. The nosepiece rotates in a manner that allows objectives of different power to be “clicked” into position in the optical path. There are grooves on the edge of the nose piece that allow it to be rotated easily. Note: do not change objective by pushing or pulling on the objective – this could loosen the objectives and result in scope or slide damage. 3. Arm and Base. These are structural elements that support the optical system. The light source is built into the base. Off to the side of the base are the combined on/off switch and rheostat which controls brightness. 4. The stage and associated parts. Stage. The stage is the plane surface on which slides are placed for viewing. Focus controls. These controls raise and lower the stage and thus vary the distance between the specimen and the objective lens (this distance is referred to as the working distance for that objective). The specimen is focused in this manner. The larger knob that moves the stage greatly when rotated is the coarse focus. The smaller knob that moves the stage only slightly is the fine focus. The coarse focus should only be used when working with low power objectives. Further, the stage should never be moved upward with the coarse focus control when looking through the microscope - doing so could damage the objective and/or slide. Such damage can be prevented by watching, from the side of the stage, to see that the slide will not touch objective when the stage is raised with the coarse focus. The fine focus control has a limited range of movement. In practice, this means that you will have situations when you will not be able to use the fine focus control to sharpen the image adequately. To correct this, rotate the 10x objective into position and then rotate the fine focus knob to the middle of its range of travel. Next, very carefully use the coarse focus to sharpen the image (this will require only the slightest movement of the coarse focus knob). Once this is done, the fine focus control should be usable. Condenser mounting bracket. This bracket holds the condenser assembly and can be moved up and down with the condenser focus control. Mechanical stage assembly. This mechanism functions to precisely move the slide from side to side and/or front to back. It is has two parts: 1. Movable slide clamp. This device is spring-loaded and “grasps” the slide by its edge. 2. Stage motion controls. These are 2 knobs (located one on top of the other) that project downward from the stage - one moves the slide from side to side and the other from front to back. Biology 05LA – Fall Quarter 2012 Lab 1 – page 3 The Optical Components. The microscope you are using has four optical components: 1) the light source, 2) the condenser lens, 3) the objective lenses, and 4) the ocular lenses. 1. The light source. Light from the sub-stage bulb is diffused by a frosted glass surface located above the bulb. Light intensity is controlled by the power/brightness knob. You will find that the amount of illumination necessary for adequate viewing is dictated by the material to be examined and the magnification used. It must be kept in mind that excessive brightness will result in a substantial loss of image contrast. 2. The condenser. The function of the condenser lens is to focus the maximum amount of light from the light source upon the specimen. Because this lens “condenses” a broad, dim circle of light into a smaller and brighter spot, it needs to be focused properly for best results. For our microscopes, the condenser is properly focused when the condenser assembly is near the uppermost range of adjustment. The function of the condenser can be demonstrated as follows: a. Plug in your microscope and turn on the illumination to an intermediate level. b. Move the condenser to its uppermost position with the condenser focus control and open the condenser diaphragm completely with its control lever. c. With the lowest power objective in position, lay flat a small (2” x 2” or so) piece of paper over the hole in the center of the stage. When looking directly at the paper (not through the scope), you should see a bright spot of light projected upon the paper. d. Observe what happens to the spot of light when the condenser is lowered and then raised again. e. At this time you should clearly understand the value of having the condenser properly focused, that is, positioned near the top of range of movement. NOTE: At one level of focus, the clear background of the microscopic field will have a grainy and colorful appearance. This “grain” can be eliminated by slightly lowering the condenser with the condenser focus control. While a properly-focused condenser contributes to a high quality image, it can also cause a potential problem when viewing living specimens. This...
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This note was uploaded on 08/27/2013 for the course BIO BIOL05LA taught by Professor Abbottl during the Fall '12 term at UC Riverside.

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