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Sensors, Pixels and Image Sizes

Cleaning Image Sensors

 
Click to see the effects of dust on your images.
 
 
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.
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 covering 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 appended 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 available from sources such as B&H and Calumet. For more information Google "cleaning image sensor" but proceed at your own risk.


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