B270 User Guide
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2.4: Locating the Specimen, and Focusing
With the specimen mounted on the stage, and the illuminator turned on, use the stage’s X-Y control knobs under the
right side of the stage to adjust the position of the specimen. The larger knob will move the specimen forward and
backward, while the smaller knob will move the specimen left and right. Compound microscopes produce inverted
images due to the nature of the optical system. Sliding the specimen towards the front of the microscope will result in
the viewed image moving in the opposite direction. Use the knobs until the specimen appears to be centered under the
objective lens. This will be the starting point.
Observation should typically begin at the lowest magnification. This provides the broadest view of the specimen. Rotate
the objective turret to set the lowest magnification lens in place. The condenser is typically designed with a range of
aperture values ranging from approximately 0.10 to 1.25. If using a 4X objective lens with a 0.10 aperture, adjust the con
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denser’s aperture using the lever on the outside of the condenser to reduce the size of the aperture. This will maximize
the focus depth. When higher magnifications are used, the aperture should be adjusted more open to better match the
objective lens’ aperture.
Look through the eyepieces, adjusting the interpupillary adjusters as needed to achieve proper alignment. Both eyes
should see the same image with a bright, round background. If the image appears offset or obscured, you should contin
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ue to adjust the interpupillary distance until the image appears correct. The left ocular tube also has a dioptric adjuster
which can be used if the eyes do not focus the same. If the eyepieces are properly aligned, but the light-source appears
offset, use the two centering screws attached to the condenser holder to adjust the condenser’s position until it is cen
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tered. For trinocular models, the photo tube can be adjusted to parfocal by first obtaining focus with the right eye, then
adjusting the length of photo tube by unscrewing the top portion of the tube from the bottom portion until the camera
obtains focus, then tightening the locking ring in the middle until it engages against the bottom portion of the photo
tube.
[image: adjusting the coarse/fine focus]
The stage should be set to a low position when mounting the specimen. Gradually raise the stage using the coarse-focus
knob. If you have already performed the height-limit adjustment, the specimen should come into focus near the maxi
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mum height. Once you begin to see shapes through the eyepieces, use the fine-focus knobs to adjust the focus until you
can see details with clarity. Use the X-Y control knobs to reposition the specimen until the area of interest is in view. You
can increase magnification as needed by rotating the objective turret. When doing so, it is advisable to watch the lens as
it is set in place to ensure it will not collide with the specimen. Slight adjustments to focus should be made at each mag
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nification, as well as to the condenser’s aperture and the illuminator’s brightness.
