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THE MICROSCOPE. Lab 2. Objetives. Be able to define the following terms. a.- coarse adjustment knob i.- field of view b.- fine adjustment knob j.- depth of field c.- stage k.- resolving power
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THE MICROSCOPE Lab 2
Objetives • Be able to define the following terms. a.- coarse adjustment knob i.- field of view b.- fine adjustment knob j.- depth of field c.- stage k.- resolving power d.- iris diaphragm l.- slide e.- ocular lens m.- coverslip f.- objective lens n.- dry mount g.- parfocal capability o.- wet mount.
Be able to construct a wet mount and focus on the specimen in the center of the field of view, using high power. • Be able to estimate the size of an object under low power or high power, given the dimensions of the fields of view. • Be able to determine the system magnification of a set of lenses, given the magnification of each separate lens. • Be able to convert micrometers to millimeters and millimeters to micrometers. • Be able to describe the function of various parts of a microscope.
Magnification • The compound microscope combines the magnifying powers of the ocular lens with the magnifying powers of the objective lens. • The magnifying power of each lens is marked on its tubular housing. • Simply multiply the magnification value that is marked on the ocular lens housing times the value marked on the objective lens housing to determine how many times your specimen is enlarged.
Microscopes often have two additional objective lenses, namely a high-power lens and an oil-immersion lens. The latter will be the longest and have the highest magnification. The oil-immersion lens will be used only after you have had special training in oil-immersion technique.
Microscope PartFunction 1- Ocular lens (eyepiece)Lens through which you view magnified specimen 2- Revolving nosepieceMovable mount for selecting objective lens best suited for extent magnification desired. 3- Objective lens. Lens on revolving nosepiece which accomplishes the initial magnification of the specimen. 4- StageFlat work surface upon which the slide is placed. Some microscopes have a mechanical stage which is used for precise movement of a slide via control knobs geared to the stage. 5- Disc diaphragmRegulates the intensity of light passing through the stage aperture and specimen.
6- Light Source A lamp beneath the disc diaphragm, provides a constant light source. 7- Stage clips Fit over ends of a slide to hold it in place. A microscope having a mechanical stage has a Lever which is opened laterally (never lifted)To secure the side surfaces of a slide. 8- Coarse adjustment knob Gives gross movement of the nosepiece for initial focus effort. 9- Fine adjustment knob Gives refined movement of the nosepiece for finishing focus. 10- Base Supports the microscope.
Resolving Power • Resolving power is a measure of lens quality. Quality lenses have a high resolving power, which is the capacity to deliver a clear image in fine detail. If a lens has a high magnifying power but a low resolving power it is of little value. Although the image may be large, it will not be clear enough to show fine detail.
Another factor that reduces resolving power is the cleanliness of the lenses. Dirt, water, or oil on the lens may scatter light and reduce the effective resolving power of th microscope. Therefore, lenses should always be kept clean. Use only the recommended paper to clean the highly polished lens’ surfaces.
Viewing and Focusing • Before you attempt to view any specimen through the microscope today, you must learn the correct use of the coarse adjustment knob. • First, click the low-power objective lens into position directly over the stage aperture. Next, watch the stage and objective lens from alongside (not through) the microscope and turn the coarse adjustment knob to close the gap between the lens and stage to a minimum.
Based upon your observation of microscope movements, and without having a specimen slide on your stage yet, determine the direction of coarse adjustment knob rotation you should use to move objective away from slide.
PROCEDURES • 1- Turn on the illuminator using the on/off switch • 2- Turn the nosepiece to bring the 4X objective (scanner) into position • 3- Raise the stage into its highest position • 4- Place a slide of the letter “e” in the slide clamp on the stage • 5- Turn the coarse adjustment knob to bring the “e” into focus • 6- Measure the field (the brightly lighted circle that you see when you look through the ocular lens) • 7- Center the ”e” in your field of view and then rotate the nosepiece to 10X • 8- Use the fine adjustment knob to focus until the image is sharp. Draw the image. Do not use the coarse adjustment • 10- Rotate the nosepiece until the 40X. Draw the image
Measurements At times it can be very useful to know the size of a specimen. This can be accomplished by using the field of view as a scale and simply visualizing it as divisible into ten equal parts. All that remains is to determine the actual length of each 0.1 of the field of view. • Use the following formula to calculate the diameter of the high power field of view: c = a x b ___________ d
CARES OF THE MICROSCOPE • When moving the microscope, carry it with 2 hands (one hand to grip the arm and the other under the base • Lenses have to be clean with lens paper (to keep them free of oil and dust). • Do not use the coarse adjustment when focusing with the higher power objectives
