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image sensors—Cleaning...

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imAge SenSorS—CleAning

When you change lenses a lot on a digital SLR, or even once in a windy or

dusty environment, dust can enter the camera and stick to the low-pass filter

covering the image sensor. This dust creates dark spots on any images you

then capture. One way to check if this has happened is to take a few photos of

a clear sky or white card. Open the images in your photo-editing program and

enlarge them to see if there are any dark dust spots in what should be even,

light areas.

The dust problem is so serious that camera companies are doing everything

they can think of to reduce it including the following:

• Reduce the dust by minimizing the dust and particles created by the
  camera itself, by using materials in the body cap and shutter that don’t create
  dust and other particles during normal wear and tear.


• Make it difficult for the dust to stick by coating the low-pass filter
  with a non-stick coating. (The low pass filter in front of the image sensor is
  designed to eliminate moiré patterns and give more accurate color.)


• Repel the dust by applying an anti-static charge to the low pass filter cov-
  ering the sensor to prevent static-charged dust from adhering to it.


• Remove the dust by attaching an ultrasonic vibrating unit to the low-pass
  filter so it can shake off any dust particles that are adhering to it. The newly
  liberated dust is then captured by an adhesive material that prevents it from
  becoming airborne again. This shaking may occur automatically when you
  turn the camera on or off, or manually when you make a menu selection.


• Put the dust out of focus. The low-pass filter, normally a single unit, can
  be divided into two layers, a front and a rear. The front layer, where any dust
  would accumulate, is positioned far enough away from the sensor so any dust
  on it will be out of focus and less likely to show in the images.


• Process the dust away. You just photograph a white wall or sheet of
  paper (or, in a pinch, remove the lens from the camera) and the camera maps
  (records) the size and position of the dust particles on the low pass filter. This
  map is then attached to all images as metadata. When the images and ap-
  pended dust data map are transferred to a computer, software supplied with
  the camera can use the information in the map to remove the effects of dust
  on the image.


• Manually clean the sensor. When all else fails your remaining choice
  is to return the camera to the camera company’s service center (tiresome
  after awhile) or clean it yourself (a high risk procedure). If you decide to do it
  yourself, you use a menu command that locks the mirror up and out of your
  way and opens the shutter so you can get to the surface of the image sensor.
  You then clean the sensor (actually the low pass filter) with sensor swabs and
  cleaning fluid developed specifically for this purpose. NEVER use compressed
  air, or other cleaning products, on the sensor. Cleaning supplies are avail-
  able from sources such as B&H and Calumet. For more information Google
  “cleaning image sensor” but proceed at your own risk.

Here are the five steps

recommended by

Photographic Solutions

for cleaning your image

sensor with their sensor

swabs and Eclipse

cleaning fluid. Courtesy

of photosol.com.

Click to see the effects

Dust on your image sensor