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Technical

December 2008

For all of the technological advances that have been made within digital SLR camera bodies in comparison to film cameras there has been one persistent issue that has taken some time to solve – dust. With a film camera dust on a frame was not a major issue – it affected just one frame and then the film was advanced to the next frame. However, since 2006, Canon has had a solution for its digital EOS cameras…

With digital sensors dust on the sensor will affect every image you take. While it may not be visible in some images, in others it can stick out like a sore thumb. Obviously the dust can be edited out afterwards on the computer but very few, if any, photographers enjoy sitting in front of a computer cloning out dust spots. Fortunately, Canon has the answer – the EOS Integrated Cleaning System (ICS). The ICS was introduced on the consumer EOS 400D camera in the autumn of 2006 and has now spread throughout the range on all models, with the sole exception of the EOS 1000D.

Three main principles

The EOS ICS works on three principles – to reduce dust generation, to repel dust sticking to the sensor and to remove any dust that does stick. The system is not just mechanical. There is also a software element that works with Digital Photo Professional – the RAW processing software supplied free in the box when you buy your Canon camera.

Reducing dust generation

Canon took a long, hard, look at dust and where it comes from. It discovered that the movements of the camera’s internal components created a significant proportion of it. To counteract this, Canon set about redesigning the interior of the camera and changing the materials used in the mirror box and shutter chamber to help to minimise any dust production. From the exterior, the most obvious change was the new body cap, made of a different material that was tougher and less likely to produce dust.

 

The dust reducing body cap.

Repelling dust

Dust is composed of very small particles that are attracted statically to the low pass filter in front of the sensor by charge on the sensor. By minimising charge in the electrical circuits of the sensor when it’s not active, less dust is pulled onto the filter.

A couple of generations back, a feature was introduced which turned off the sensor when the lens was removed to help cut down on static charge while the lens mount is uncovered. However, this is not the whole story. Canon has also employed anti-static coatings on the low pass filter. The EOS 50D and EOS 5D Mark II cameras go even further by using a fluorine coating on the low pass filter to help to stop dust being able to stick. Any dust that does get stuck to the filter surface will throw a shadow onto the sensor and this is what the dust spots you see in images are. To help to avoid this, the low pass filter assembly in EOS cameras has also been moved further away from the sensor so that any shadows there are more blurred and less distinct.

Removing dust

 

The self-cleaning sensor unit from an EOS 5D Mark II.

The most talked about part of the whole ICS system is the piezo-electric mechanism that shakes the dust from the sensor. If dust does manage to make its way through the barrage of anti-dust measures and adhere itself to the low pass filter it is then removed by the filter cleaning system. Since most dust is airborne, and only weakly attracted to the low pass filter, it is possible to shake it off using high frequency, ultrasonic vibrations. It’s not the sensor that is shaken, but the low pass filter where the dust is trapped.

Using the menu system for sensor cleaning, there are several options. You can select to have sensor cleaning every time you turn the camera on and off, or to ‘Clean Now’, which activates a cleaning cycle, or even to perform a manual clean. If you select to have the camera perform a cleaning cycle every time you switch it on and off, which is the recommended setting, it will not interrupt your shooting. When you turn the camera on, it performs a sensor clean, but as soon as you press the shutter button it stops and is ready to shoot.


 

The display you’ll see on the LCD monitor for a couple of seconds during an Integrated Cleaning cycle.

The most common question is “Where does the dust go?” When the ICS activates, the dust falls off the sensor and is subject to gravity – this is why you should always try to place the camera on a flat surface or hold it so that the lens is pointing forwards. The dust is then trapped on sticky pads surrounding the filter assembly. These sticky pads are a lot like double-sided tape, but are industrial strength and should last for the lifetime of the camera. The dust is caught there and stuck so that it cannot fall back onto the filter assembly.

Software processing

The final stage in the battle against dust is software processing. While it is possible to remove dust spots by cloning them out in Photoshop, the Canon system and software can do this automatically.

Dust Delete Data is a small data file that you can create to append to each image as it is taken. It is essentially a map of the sensor and where any dust is located. To create the Dust Delete Data, you’ll need a piece of white paper and a lens with a focal length that is greater than 50mm. Point the lens at the white paper, set the lens to manual focus and adjust the focus to infinity. Go to the Dust Delete Data option in the menu and select ‘Ok’. The camera will perform an automatic sensor cleaning cycle, then there will be a shutter sound, but no picture will be taken. This is the camera mapping the position of any dust on the filter. This data can then be appended to every image so that Digital Photo Professional software can use it to automatically remove any dust spots.

 

The Dust Delete Data screen.

Does ICS work?

All of the evidence points to the EOS ICS being highly effective and much appreciated by photographers. Feedback from users in the field say it has freed them up from having to manually clean their sensors, and it has also cut down on the time that they have to spend cloning dust spots out of their images. While it cannot remove all types of dust, it removes a significant amount of what gets onto the filter and that is a major timesaver.


Technical

How to test for dust

If you don't often see dust in your images, but want to know if there is dust on your filter, there is an easy way to test. Take the longest lens you have, ideally a telephoto longer than 200mm, set the focus to manual and focus as close as the lens will allow you to. Set the camera to Av mode and set the smallest aperture possible - for example f/22. Now take a picture of a clear part of the sky. If you look at the image on the computer, you will be able to see if and where any dust might be.