Possible problems and causes
Vignetting (dark corners of print):
The
microscope may not be adjusted for
Koehler illumination; the field diaphragm
may not be opened far enough to fill the
field of view.
Image sharp only in center:
May be due
to incorrect objective lens for
photomicrography. Check that the
microscope has a flat-field (also called
“plan” or “plano”) objective.
Also may be caused by chromatic
aberration. If using an older microscope
that has a correction for chromatic
aberration in the eyepiece, contact
Polaroid Technical Assistance for
information about an adapter.
Hot spot (light) in picture:
May be
caused by a low-power objective lens or
the field not evenly covered by the light
cone. If possible, remove the front
element of the condenser. A diffuser in
front of the lamp (or over the field
diaphragm) may help. Also, check the
positioning of the lamp itself. Sometimes
a rotation or a slight change in position
will help uniformity.
This also may be caused by the
substage diaphragm not being closed
down. Close the diaphragm only until you
notice a change in brightness; further
closing will cause a loss of resolution.
Dirt on the condenser can also cause
“hot spots.”
Dirt
One of the most common causes of
picture defects is dirt—on the specimen,
microscope lenses or camera.
•
Dirt on the microscope lenses is not
always readily diagnosed. Dirt on the
objective lens may result in an image that
is unsharp overall and lacking in contrast.
Dirt on the collector or condenser lenses
will usually appear as blurred spots or
specks. Dirt on the collector or field
lenses will become more or less sharp
with the specimen as the condenser is
focused. Clean each microscope lens as
recommended by the manufacturer.
•
Dirt on the camera’s developer rollers will
produce a repeated pattern of spots or
bars across the image. Clean the rollers
with a soft, lint-free cloth, dampened with
water. Never use cleaning solvents.
•
Dirt on the mirror inside the camera will
appear as well-defined spots on all prints
in approximately the same location. To
clean the mirror, open the camera and
remove the film pack. Carefully remove
specks with a clean, soft brush or cotton
swab, or use compressed air.
•
Dirt or dust particles on the specimen
may either be in focus (and magnified)
with the specimen or produce
out-of-focus areas in the image. They are
easily located by moving the specimen
across the field of view; cleaning
techniques are dependent on the type of
specimen.
•
Dirt on the camera lens will be visible
through the viewfinder; rotate the camera
slightly while looking through the
viewfinder. Dirt on the lens will move as
the camera is moved. This dirt will appear
on pictures as out-of-focus shadows.
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