Levenhuk MED 25 Serie Bedienungsanleitung Seite 6

Levenhuk MED 25 Microscopes
General Information
Read the user manual carefully before you start working with a microscope. Levenhuk MED Series biological microscopes are
safe for health, life and property of the consumer and the environment when properly used, and meets the requirements of
international standards. These microscopes are designed for observing transparent objects in the transmitted light using the
bright field method and the dark field method. They perform well in clinical research and tests; teaching demonstrations;
bacterioscopy and cytology in medical and health establishments, laboratories, universities; and may be used for scientific
research in agriculture and microbiology.
Microscope assembly
• Unpack the microscope carefully and place it on a flat surface.
• Remove the plastic bags and dustproof cover of the eyepiece head.
• Install the binocular or trinocular head and tighten the locking screw.
• Inspect all the items included in the kit and define their purpose.
• Connect the power cord to the microscope and plug it in.
Microscope use: The bright-field method
Please refer to the fig. 1а (binocular model) and fig. 1b (trinocular model).
• Turn on the power and the illumination will turn on. Set the brightness at approximately 70%. Place the specimen on the
stage. Make sure the clips hold the specimen firmly in place.
• Iris diaphragm should be adjusted in accordance with numerical aperture of a lens. The best practice is to make the iris
diaphragm slightly smaller than the aperture of the selected lens. Open or close the iris diaphragm using the adjustment
screws. If the adjustment screw is turned to the right, the iris diaphragm is fully open. Note: The diaphragm is not intended
for adjusting the brightness of the illumination. To adjust the brightness, use the brightness adjustment knob.
• Slide the filter holder, place the filter in it and then return the holder to its initial position.
• To change the objective magnification, turn the revolving nosepiece until it clicks.
• Make sure that the lens does not touch the sample when adjusting the focus: Rotate the coarse focus knob until the
specimen is about 3.175mm (1/8") away from the lens.
• Looking into the eyepiece, slowly turn the coarse focusing knob until you can see the image of the observed specimen. Turn
the fine focusing knob to make the image clear. The fine focusing mechanism allows you to focus on the observed specimen
while using high magnifications.
• When you use an oil immersion objective, the space between the specimen and the lens should be filled with immersion oil.
Raise the condenser to the upper position and put a drop of oil on the lens and on the cover glass of the specimen. Move the
revolving nosepiece back and forth to get rid of air bubbles in the oil. Then, fix the objective lens in its working position.
Make sure that oil fills the entire space between the objective lens and the specimen. After use, wipe the lens dry.
• To adjust the position of the mechanical scale, turn the coarse focusing knob in a clockwise direction if you want to fix the
position of the mechanical scale, or in a counterclockwise direction if you want to loosen it.
• To place the specimen in the field of view, move the stage horizontally back and forth or left and right using the stage
moving knobs.
• Look through the right eyepiece with your right eye and adjust the image sharpness with the coarse and fine focusing knobs.
Then, look through the left eyepiece with your left eye and rotate the diopter adjustment ring to equalize the difference
between your left and right eyes vision. Remember the setting for future use. Adjust the distance between the eyepiece
tubes of the binocular head so that the image merges into a single circle.
• Trinocular models: You can install the digital camera to the third eyepiece tube. Use the beam splitter to send the light to
the eyepieces or to the camera.
Dark field condenser (oil)
Configuration and operating principle
Please refer to fig. 3. The device is designed for studying low-contrast objects that are not visible in the microscope when
observed in normal light conditions using the bright field method. The dark field method allows you to observe very bright and
transparent objects in scattered or reflected light.
The dark field condenser is a system of lenses inserted into the cylinder. The cylinder is placed inside the microscope body on
the moving ring. This ring is a centering device, which can be controlled with adjustment screws located on the outside of the
microscope body.
The light from the illuminator, passing through the dark field condenser, is converted into a cone-shaped beam and directed at
the observed specimen. Almost all of the light passes through the lens and forms an image only by the light scattered by the
structure of the specimen. Therefore, in the field of view of the eyepiece, the bright contrast areas of the specimen structure
are displayed on a dark background.
Assembly and using
• Install a dark field condenser instead of the standard condenser of your microscope.
• Install the desired eyepiece and choose the objective with the lowest magnification.
• Put a drop of oil on the condenser lens; fix the microscope slide on the stage. Note: It is recommended to use a coverslip
with a thickness of 0.8—1.2mm.
• Raise the dark field condenser until the immersion oil meets the stage and then focus.
• If you see an off-center light spot, use the adjustment screws to bring it to the center of the field of view.
• Note: The aperture of the objective lens used must be smaller than the aperture of the condenser.
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