43
III. Operation of Each Part
2. Field Diaphragm in the Epi Illuminator
The field diaphragm restricts illumination to the area
of the specimen that is being viewed. Operating the
field diaphragm open/close lever changes the size of
the field diaphragm. For normal observation, the size
of the diaphragm should be such that it circumscribes
(or inscribes) the edge of the viewfield. If a broader
area than necessary is illuminated, stray light will
enter the optical system, creating flaring, reducing the
contrast of the optical image.
Appropriate field diaphragm settings are particularly
important for photomicrography and digital image
capturing. In general, good results will be obtained by
stopping down the field diaphragm to settings slightly
wider than the area to be reproduced within the photo
frame or monitor display.
Centering the field diaphragm
1 Perform steps in Page 18, “4 Episcopic Microscopy (with the Epi Illuminator Option)” and
focus on the specimen using the 10x objective under the episcopic illumination.
2 Lower the field diaphragm open/close lever to stop down the field diaphragm.
3 Turn the field diaphragm centering screws (on both sides) so that the field diaphragm image
is positioned in the center of the view field.
4 Adjust the field diaphragm image with the field diaphragm open/close lever and centering
screws so that it inscribes the view field.
5 To observe the specimen, raise the field diaphragm open/close lever so that the field
diaphragm image circumscribes the view field.
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Field diaphragm
open/close lever
Field diaphragm centering screw (both side)
Field diaphragm
image
Eyepiece viewfield
Field diaphragm image
Eyepiece view field
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