sample (object)

1
1- bring sample into focus with objective focus
knob 2- close field diaphragm to minimum
size 3- focus condenser until you can see a
clear image of the field diaphragm (open and
close field diaphragm to check, center as
needed) 4- open the field diaphragm until the
field of view is just completely
illuminated 5- now adjust light intensity and
the condenser diaphragm to optimize image small
aperture in condenser diaphragm gives best
contrast, large aperture gives best resolution
(default starting point is for condenser aperture
to fill ¾ of objective back plane, this can be
viewed with special telescope eyepiece).
Notes Do not adjust light intensity with field
or condenser diaphragms, use the condenser
diaphragm to optimize contrast and resolution,
adjust lamp voltage to correct light intensity.
image point for o1 and ?2
image point for o2 and ?1
diaphragm open
diaphragm closed
back plane of objective lens
front of objective lens
sample (object)
condenser lens
condenser diaphragm (focused at back plane of
objective)
field diaphragm (focused at object plane)
collector lens
Why do we use Kohler illumination? For even
intensity at the object and image, we want each
small part of our source to contribute to all
parts of the image and we want each small part of
our image to be made up of light from all areas
of the source. We dont want to see the shape of
the light source in our image! What would we
see if light rays from A1 and A3 were focused
at the object/image planes?
Light source (filament)
adapted from Murphy 2001 and Nikon microscopy
websitehttp//www.microscopyu.com/tutorials/java/
kohler/index.html