Camera Lens and Sensor Cleaning Aids
The imaging sensor on digital cameras can get dirty by collecting dust particles. A representative at Canon told us that since the sensor is an electrostatic device it attracts dust. Dust can land on the sensor anytime you expose it to outside air by changing lenses. Dust spots will show up on an image as dark areas that are on every picture taken with the camera. The dust spots are apparent on the image below taken with a Canon 30D. Look in the center of the picture on the horizon and below it.
Example of a Dirty Sensor
The camera used for the picture was particularly dirty, even though it was less than a month old. The dust will show up more with a stopped down aperture (high f number) and focus set at infinity. I check for dirt by taking a picture of a uniform background with f/32 (or as high as the camera will go), focus at infinity, and a long exposure time. Moving the camera in a circular pattern while the shutter is open will remove any non-uniformity from the background image. The picture below is the same camera as above after an attempt at cleaning it myself.
Uniform Background, f/22, Infinity, 2-4 second exposure.
If you then do a histogram equalization, the dust becomes very apparent!
Now that is one dirty sensor! As you can see though, many of the dust particles don't effect the image. Only the biggest pieces show up in a final image. With lower f-numbers and focus set closer, the dust will almost disappear.
Canon suggests using ONLY a dust blower to clean the sensor.
For an example of a good dust blower: Visible Dust Hurricane Blower
This is a better dust blower: Rocket Blower
Canon also warns; never put the tip of the blower below the shutter curtain in case the power goes off or for some reason the curtain decides to close, you can damage the camera. The problem with the blower method is that it doesn't work. They also warn; don't try to use canned dust removers, like keyboard cleaners, because they can "spit" liquid and damage the sensor. For the best "risk free" cleaning, the camera must be returned to a Canon service center.
Although there is some risk to cleaning the sensor yourself, some people will clean it themselves. Most optical engineers have their own "secret formula" for cleaning lenses and sensors. The biggest risk is a scratched sensor, which is VERY expensive to fix.
If you live a long way from a service center or decide to clean the sensor yourself, you can buy special cleaning swabs which are made for this purpose. The swabs are assembled in a clean
room and sealed. The chance that they will scratch the sensor is very low. They are sold under
the name "Sensor Swabs" and are made by Photographic Solutions Inc. You can also
buy special cleaning fluid which will not damage the sensor or leave residue.