Possible problems and causes

12English

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.