Is that white spot a ghost?
September 15, 2007
One of the major shortcomings in compact camera design is the close proximity of the flash to the lens. The most common problem caused by this design is red-eye. A second problem directly related to the close flash/lens proximity is the presence of random white circles appearing in images. A universal term does not exist to explain these circles though I like to refer to them as “ghost spots” because they’re semi-transparent and appear in different locations in subsequent images. The explanation for this second flash-related problem is very similar to that of the red-eye phenomenon.
Ghost spots are created when light from the flash reflects back off of dust particles floating in the air close to the camera. Because the lens is focused on a subject further away than the dust particle, the illuminated particle is out of focus and appears very large in the form of a white circle. The close proximity of the flash to the lens makes compact cameras more susceptible to this problem than DSLRs. The problem is also common with wide-angle lenses because of the wide field of view.
The following image is an example of ghost spots. The background is an auditorium curtain.
Common particles that cause ghost spots include:
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dust
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smoke
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pollen
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moisture in the air
To eliminate or reduce the number of ghost spots you can use the following methods: (note that many of the following are the same methods used to reduce red-eye)
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Turn on more lights. Having more ambient light allows the flash to fire at a lower power.
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Increase the shutter length. A longer exposure will capture more ambient light and the flash can be fired at a lower power.
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Increase the ISO setting so the flash can fire at a lower power.
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Turn off the flash if there is enough ambient light.
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If your camera allows for it an externally mounted flash will increase the distance between the flash and lens.
