Finding and Removing Debris and Smudges

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If there is an unwanted artifact (dust, debris, fingerprint, smudge, etc.) visible when using a microscope, you can identify its location by doing a few tests and examining its characteristics. It is common for these artifacts to be inconspicuous when using low magnifications but strongly visible at 40X and above.

The first step in identifying an artifact is determining how close to being in focus it is.

In Focus Artifacts[edit]

If the artifact is in focus, it is likely close to one of the image forming conjugate focal planes:

  • The field diaphragm
  • The specimen (or cover glass or slide)
  • The intermediate image plane (the back of the eyepiece)
  • The sensor of the camera, if you are using one
  • The retina of your eye

The less sharp the focus on the artifact is, the farther it will be from these planes. For example, a speck of dust on the prism in the head close to the eyepiece will likely be less sharp, while a speck on the back of the eyepiece may be very sharply in focus.

Try the following procedure:

  1. Start by checking the camera if you are using one. Twist the camera a little without moving the microscope. If the artifact does not move, it is in the camera, potentially in contact with the sensor.
  2. If you are using an eyepiece, twist it. If the artifact moves, it is on the eyepiece (either the front or back). This is perhaps the most common place to find debris or smudges that show up visibly at high magnifications. If you are using a binocular head, check if it is in one side by closing one eye, then the other. Try exchanging the right and left eyepieces.
  3. Move the slide. If the artifact moves, it is on the slide, specimen, or cover slip.
  4. Consider whether you might be seeing floaters or macular degeneration in your eye.
  5. Otherwise, look at the mirror or optics near the field diaphragm (or just above the light source, if you do not have a field diaphragm).

Places That Do Not Cause Artifacts[edit]

Debris near the aperture conjugate planes is unlikely to result in a distinguishable artifact. Instead, the likely result is a loss of contrast, clarity, or focus. The aperture conjugate planes are:

  • The light source, if using Koehler illumination
  • The condenser aperture diaphragm (or condenser lenses in general)
  • The back focal plane of the objective

Dust or scratches on the objective front lens do not generally show up as artifacts in the image, but may reduce overall image clarity.