Dust in CMOS sensor
Have you ever experienced when you had taken a picture and the result is like this?
[Canon 350D, Canon EF 28-135mm IS USM @ 85mm, f/22, 0.5s, ISO 100]
Did you notice little black spots scattered around in the above picture? Take a look carefully above the Mt. Sopris. Yes, they are specks of dust in our CMOS (sensor) camera and our Canon 350D was just 3 months old !! We bought it brand new. We thought initially that maybe our CPL filter got some dirt, but it was wrong. So we thought maybe it is the lens and it was also wrong, until we got to the conclusion that they are dust in our camera sensor.
So why does our new camera sensor has already contained dusts? For the record, we only have 1 lens during our trip to USA in July 2005. We had had 2 Sigma lenses before we bought Canon EF 28-135mm lens and that might be the reason for the dust in our camera sensor. And finally, how can we clean the dust?
The following article will explain about how to test your camera whether there are dusts in your sensor, followed by how the dust can go into the sensor. Is it normal ? Finally I will list some sites that explains in detail how to clean the sensor.
I am going to explain the cleaning process by taking some popular cleaning methods from the internet, also with some popular cleaning products. Pros and cons are going to be explaied. You can always go to your camera's service center to clean your camera sensor. Our camera has not been cleaned yet, because we think that we can live with the dust as they are not so badly worried. The clone and stamp tool from our post-editing software can still solve this problem.
Testing dust in the sensor
To test whether your camera sensor has speck of dust:
Below are our test results. We took 4 examples, i.e. f/8.0, f/11, f/16 and f/22. The result shows that the speck of dust appears in our camera starting from f/16, but it actually appears at f/11 if we look at the 100% image.
[Click the above images will show the larger version]
How does dust comes to the camera sensor?
Actually the dust does not directly go into the sensor itself, but it sticks at the outer surface of a filter glass. That is why we see the dust on small aperture, because the light comes just like a spotlight, creating a hard edge on the dust. When we use wide aperture, the light goes more diffuse which makes the dust hardly visible.
Most of the time, the dust comes when we change lenses, especially in the field. Thus if we do not necessary to change a lens, then it would be better not to do so. When we go to a certain photography task, we usually know what we will encounter. Preparing the most appropriate lens first at home, when the environment is still clean, is then the best way to reduce dust to come to your sensor.
Nevertheless the dust sooner or later will come to your sensor. This is because the CMOS uses magnetic field which attract small particle of dust to come. This is the life that every digital photographers must encounter.
Cleaning methods
Basically these are the popular methods to clean your sensor:
[Canon 350D, Canon EF 28-135mm IS USM @ 85mm, f/22, 0.5s, ISO 100]
Did you notice little black spots scattered around in the above picture? Take a look carefully above the Mt. Sopris. Yes, they are specks of dust in our CMOS (sensor) camera and our Canon 350D was just 3 months old !! We bought it brand new. We thought initially that maybe our CPL filter got some dirt, but it was wrong. So we thought maybe it is the lens and it was also wrong, until we got to the conclusion that they are dust in our camera sensor.
So why does our new camera sensor has already contained dusts? For the record, we only have 1 lens during our trip to USA in July 2005. We had had 2 Sigma lenses before we bought Canon EF 28-135mm lens and that might be the reason for the dust in our camera sensor. And finally, how can we clean the dust?
The following article will explain about how to test your camera whether there are dusts in your sensor, followed by how the dust can go into the sensor. Is it normal ? Finally I will list some sites that explains in detail how to clean the sensor.
I am going to explain the cleaning process by taking some popular cleaning methods from the internet, also with some popular cleaning products. Pros and cons are going to be explaied. You can always go to your camera's service center to clean your camera sensor. Our camera has not been cleaned yet, because we think that we can live with the dust as they are not so badly worried. The clone and stamp tool from our post-editing software can still solve this problem.
Testing dust in the sensor
To test whether your camera sensor has speck of dust:
- Find an object that has constant luminosity. A white paper might be good one. I prefer a bright blue sky, because it has sufficient light for proper exposure. If you use a white paper, then you might need extra light, such as flashes. The result might not have a constant luminosity.
- Set focus to infinity.
- Set the lowest ISO as you might not to interfere the speckle dust with sensitivity noise.
- Use the highest resolution of your camera.
- If you have tripod, then it might be good, because you're going to use the smallest aperture.
- Use Av priority method and select the widest aperture available of your lens.
- Take a picture.
- Stop down the aperture and repeat step 5 until the smallest aperture of your lens.
- Examine the pictures.
Below are our test results. We took 4 examples, i.e. f/8.0, f/11, f/16 and f/22. The result shows that the speck of dust appears in our camera starting from f/16, but it actually appears at f/11 if we look at the 100% image.
 f/8.0 |  f/11.0 |
 f/16.0 |  f/22.0 |
[Click the above images will show the larger version]
How does dust comes to the camera sensor?
Actually the dust does not directly go into the sensor itself, but it sticks at the outer surface of a filter glass. That is why we see the dust on small aperture, because the light comes just like a spotlight, creating a hard edge on the dust. When we use wide aperture, the light goes more diffuse which makes the dust hardly visible.
Most of the time, the dust comes when we change lenses, especially in the field. Thus if we do not necessary to change a lens, then it would be better not to do so. When we go to a certain photography task, we usually know what we will encounter. Preparing the most appropriate lens first at home, when the environment is still clean, is then the best way to reduce dust to come to your sensor.
Nevertheless the dust sooner or later will come to your sensor. This is because the CMOS uses magnetic field which attract small particle of dust to come. This is the life that every digital photographers must encounter.
Cleaning methods
I wish Canon has adapted Olympus' method to clean the dust using the supersonic wave filter then we would not have this nightmare of cleaning dust in the sensor by ourself.There are numerous sites explaining how to clean sensor from dust. They are great to learn so I will not try to reproduce them. Instead, I am going to summarize what are the possibilities and the pros & cons about it.
Basically these are the popular methods to clean your sensor:
- Bring your camera to the service center if you have still a guarantee. This is the only method that is supported by Canon.
Pros: it's free if you still have the guarantee, pure clean or at least has a very small dust.
Cons: you might have in about 2-3 weeks without camera. - Air brush (blower brush). It uses a high pressure air to blow into your sensor in a hope that the dust will be blown away. Note: do not use a blower with air compression because it might have some water that will spit into your sensor. Then you have a bigger problem.
A popular air brush product is the Giottos rocket air blower.
Pros: safer, no physical touch with the sensor thus avoiding scratch on the sensor.
Cons: it is random, because you might end up with more dust than before. - The copperhill method. It uses a sensor sweep, wrapped by an ultra soft micro-fabric pec-pad. Before you swap the sensor sweep in the sensor, you put a few drops of cleaning liquid (Eclipse) onto the pad.
Pros: a popular method and cheap.
Cons: risky because you must press the sweep in the sensor, need a lot of practices. - Static brush. Since the dust has a electrostatic, by using a special brush that has been previously charged the dust can be be lifted up. Altough you touch the sensor by the brush, you do not have to press it against the sensor, because it does not use any liquid.
A popular static brush is the Sensor Brush.
Pros: safe and very effective, the brush can be used for many times.
Cons: it is very expensive at the moment for a single brush.
- Brush your sensors from Petteri's Pontification.
- The famous CCD/CMOS Cleaning Photos with instructions from Nicholas R or it's said the Copperhill method.
- User experience on cleaning his Canon 10D sensor.
- Digital Camera Cleaning Technique.
posted by Pak Sui at Tuesday, August 09, 2005
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