Monday 16 June 2008

Sensor cleaning

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DISCLAIMER: The only method Canon recommends for sensor cleaning is using a Giottos-type air blaster. Any other will invalidate your warranty. The following procedure carries the risk of sensor damage.

There are many advantages of the digital format over film but one angst-inducing problem that goes with the territory is sensor dirt. Even though I keep all my lenses very clean and exercise caution when changing lenses on my Canon EOS 5D, dust and dirt manages to sneak in, and I have to clean the sensor about every 6 months. There is risk involved with this procedure but I don't want to be sending my camera back to Canon for a clean every time. Shown above is my cleaning kit - a Giottos Rocket Air blaster, a 12-pack of Sensor Swabs (type 3 for the 5D) and Eclipse E2 cleaning fluid (for tin oxide coated sensors such as the 5D) - it cost me about £55 in total.

Most digital SLRs have a sensor cleaning mode which will lock the mirror up and open the shutter curtain to give you access to the sensor. Always make sure your batteries are fully charged before attempting this - if power fails the shutter will try and close. The air blaster should be your first port of call since you don't need to come into contact with the sensor. Hold your camera with the sensor facing the floor (so that gravity is on your side) and blast it with air - keep the tip of the blaster outside the body of the camera. This will remove any loosely attached pieces of dirt and may solve your problem. If you want to check if this is the case, take a shot of a plain-coloured surface with your lens stopped down to its smallest aperture. You can then import the shot into Photoshop and play with contrast and levels to enhance any specks in the image. Bear in mind that this is a very stringent test and most sensors will probably look dirty - is the dirt really an issue? Use your camera with typical settings for a few shots - can you see any specks? If you can and the images require clean-up in Photoshop then you may want to proceed to the next step.

Some dust seems to get welded to the surface of the sensor or, more accurately, the low-pass filter which covers the sensor, and no amount of air-blasting removes them. The sensor swabs are lint-free pieces of material attached to plastic paddles that are assembled in a clean room - buy the type that matches your sensor size. The E2 cleaning fluid is ultra-pure methanol or ethanol which leaves no residue on the sensor. In combination they reduce the likelihood of you introducing further contamination, increase the chance of you cleaning the sensor first time and reduce your stress levels. Like many things in life, the procedure is not risk-free. You wet the swab with a couple of drops of cleaning fluid, carefully bring the swab into contact with the sensor, and then sweep the swab over the surface (full instructions come with the pack). I had to use a couple of swabs on one occasion when my sensor was very dirty but it did the job.

If you don't feel confident about this, you can always send your camera to Canon to be cleaned.

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