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(10) Adjust the brightness with ND filters and the lamp
intensity control dial.
( 11) Turn the field diaphragm dial to stop down the
field diaphragm until the field diaphragm image
almost inscribes or cicumscribes the viewfield.
*
The fi e ld diaphragm restricts the illumination light
only to the sample's area to be illuminated for
observation. If the sample is illuminated wider than
necessary because the field diaphragm is not stopped
down properly, stray light will enter the viewfield to
generate a flare, and reduce the image contrast.
Correct operation of this diaphragm is therefore very
important especially for photomicrography.
Usually, the field diaphragm is to be stopped down
until the image of the stopped down diaphragm is
slightly larger than the actual dimensions of the film
format.
(12) Turn the aperture diaphragm dial to open or stop
down the aperture diaphragm properly.
*
The aperture diaphragm is used to adjust the
illumination system's numerical aperture, and plays an
important role in determining image resolution,
contrast and depth of focus. Detach one of the
eyepieces from the binocular eyepieces of this
microscope, and look into the eyepiece sleeve. The
objective's exit pupil is visible there. As a general
rule, the aperture diaphragm is stopped down to the
range of 70-80% of that exit pupil to obtain a good
image of appropriate contrast.
12V-100W
lamphouse
Aperture diaphragm dial
Field diaphragm dial
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rt"n � � �� � ,;�:.,,
II 111" 11)1 1
Objective's exit
pupil
Aperture
diaphragm image
Size of the aperture diaphragm image
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1
0
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I
300
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26
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