Biomedical Engineering Reference
In-Depth Information
Köhler illumination
Illumination
light path
Image-forming
light pat
h
Film plane
Lens
Film plane
Eyepoint
Eyepiece
Fixed
Diaphragm
Eyepiece
Intermediate
image plane
Objective
back focal
plane
Objective
Sp
ecime
n
slide
Specimen
Aperture
diaphragm
Substage
condenser
Field
diaphragm
1. 3
Köhler illumination and image-forming light paths.
constructive and destructive interference occurs which appear as light and
dark regions in the fi nal image. If we place a stage micrometer in the light
path of the microscope with the substage aperture diaphragm closed down,
remove the ocular from the eyepiece tube and look at the back focal plane
of the objective, we see the diffraction image of the stage micrometer. This
image consists of a bright central spot of light which is the image of the sub-
stage condenser aperture and several fainter colored images of the aperture
diaphragm on each side of the central spot. The diffraction image at the
back focal plane of the objective is shown in Fig. 1.4.
The fainter, colored areas are constructive interference by light of
the same wavelengths and the dark areas in between are destructive
