MICROSCOPE.pdf

MICROSCOPE Used to magnify objects that are too small to be seen by the naked eye. 1. MECHANICAL PARTS o Parts that support the whole device 1. Adjustment screws – two pairs of wheels attached to either side of the body tube. a) Coarse adjustment screw: bigger wheel used to adjust...

MICROSCOPE Used to magnify objects that are too small to be seen by the naked eye. 1. MECHANICAL PARTS o Parts that support the whole device 1. Adjustment screws – two pairs of wheels attached to either side of the body tube. a) Coarse adjustment screw: bigger wheel used to adjust low power objective in focusing. b) Fine adjustment screw: smaller wheel used for delicate focusing in connection with the high power and oil immersion objectives. 2. Base: Y or U-shaped stand that supports the microscope. 3. Draw tube: the upper smaller end of the body tube bearing the eyepiece or ocular. 4. Body tube: The cylindrical structure vertically arising from the handle. It holds the dust shield and nosepiece with the objectives at the lower end. 5. Handle/Arm: The curved metallic part arising from the pillar. Used to hold the microscope. 6. Dust shield: A thin circular structure above the nosepiece used to protect the lenses of the objectives. 7. Revolving Nosepiece: Holds the objective lenses and attaches them to the microscope head/body tube. This part rotates to change which objective lens is active. 8. Stage: The flat platform where the slide is placed. 9. Stage Clips: Paired structures on either side of the stage used to hold the slide in place. 10. Inclination joint: Found at the junction of the pillar and the handle. Used to tilt the microscope. 11. Pillar: A short piece of metal attached to the end of the base. It also supports the microscope. 12. Mirror rack: Found below the stage and attached to the pillar used to hold the mirror. 2. MAGNIFYING PARTS System of lenses at the draw tube through which the observer peeps during actual focusing 1. Ocular/Eyepiece: Found at the draw tube through which the observer peeps during actual focusing 2. Objectives: tube-like structures attached to the revolving nosepiece. These are primary lenses that magnify the specimens. o Four objective lenses are present in the compound light microscope. a) Scanner (4x): The shortest tube that forms a whole view of the specimen. b) Low Power Objective (10x): Slightly longer tube that forms a bigger image of the object. c) High Power Objective (40x): Next longer tube that gives much enlarged and more detailed view of the specimen d) Oil Immersion Objective (100x): Another objective as long as the HPO but with a much bigger degree of magnification. The lens is used with an immersion oil or cedar oil. Total magnification = Objective Power x Eyepiece Power 3. ILLUMINATING PARTS − Provide light or illumination to the specimen and optical parts 1. Abbe condenser: A lens found immediately beneath the hole of the stage. Used to concentrate light rays into the specimen. 2. Iris diaphragm: Found below the stag consisting of regularly arranged circular blades. The opening could be adjusted to regulate the amount of light reflected by the mirror on the object. 3. Mirror: Found below the stage near the base provided with concave and plane surfaces. Used to collect and direct light to the object. 4. MAINTENANCE AND CARE 1. Use both hands in carrying the microscope. Hold the handle with one hand and support the base with the other. Never swing the microscope. Any part maybe detached and you will be held responsible for any destruction resulting from such detachment. 2. Never allow water and chemicals to come in contact with the lenses or metallic parts. 3. Use tissue or soft paper to clean the lenses 4. Place the microscope away from the end of the table. When not in use, never leave it on a tilted or inclined position. 5. Do not force any part of the microscope to remove. Call your instructor to check the microscope in case of difficulty on focusing. 5. HOW TO USE THE MICROSCOPE 1. Set Up the Microscope 2. Clean the Lens 3. Prepare a Slide 4. Insert the Slide 5. Set Up for Viewing 6. Set the Light Control 7. Focus the Microscope 8. Increase Magnification 9. Switch to High Power 6. TERMINOLOGIES IN THE USE OF THE MICROSCOPE 1. Microscope field of vision − Luminous white circular area seen through the ocular where the image of the specimen is seen. 2. Magnifying power − The capacity of the lens to enlarge the size of the specimen’s image. 3. Magnification − Ratio of the apparent size of the image, and the actual size of the specimen 4. Total magnification − Product of the magnifying power of the eyepiece and objective being used. 5. Numerical aperture − Measurement of the angle of the maximum cone of light that may center the lens. 6. Resolution − Refers to the finest detail actually visible in the image, roughly comparable to pixel size: the smaller the pixels, the finer the detail visible in a computer image. 7. Resolving power − The ability of the lens to clearly separate or distinguish two points or two lines individually in the image. 8. Limit of resolution − Minimum distance between two points that allows for their dissemination as two separate points. 9. Contrast − The difference between the brightness of various details in the object, and the difference as compared with the background. 10. Working Distance − The distance between the bottom of the lens and the top of the cover glass when the specimen is focused under the objective in question. 11. Principal focus − The point where rays parallel to the principal x-axis of the lens (with spherical surface) are brought into a focus (or meet). This focus is real for convex lens and virtual for concave lens 12. Focal length − The distance of the principal focus from the center of the lens. Relationships: High magnification needs high resolution High resolution needs high numerical aperture High NA contributes to better contrast High Magnification requires a short focal length lens (short working distance) Low Magnification requires a long focal length lens (long working distance)