Dean M. Chriss
Photography

DSLR Image Sensor Cleaning
Four Methods, and More
August 20, 2013

Horseshoe Falls and Cormorant, Niagara Falls, Ontario, Canada
Horseshoe Falls and Cormorant, Niagara Falls

Background

Dust happens, and anyone who uses a digital SLR camera will eventually need to clean their camera's image sensor. You should be aware that when we talk about cleaning the image sensor we are actually talking about cleaning a filter that covers the electronic CMOS or CCD element, which is the thing that actually produces your images. There is legitimate concern about scratching this filter since any mark on it will show up on every image captured by the camera, but the dangers are often overstated. The best chance of scratching it happens when a piece of hard grit gets trapped in a cleaning tool and is wiped across the filter surface. This is why it is important to keep all cleaning tools clean and blow any loose particles off of the sensor with air before cleaning by any method that uses wiping. Still, this is not rocket science or brain surgery. It takes only a few basic tools and common sense to do an impeccable job.

Not All Spots are Created Equal

Most spots that are visible on digital images are simply dust of one kind or another that floated into the camera body when changing lenses, were carried in on the back of the lenses and body caps, or were created inside the camera itself. Some of this dust is sticky, like pollen or oily soot particles from diesel exhaust. Sometimes tiny droplets of excess camera lubricant find their way to the sensor's filter. Some spots are liquid or deposits left by evaporated liquid, produced by very tiny droplets like those that make fog. Still more dust is produced by the camera as its internal mechanisms wear. Some non-oily dust sticks to the sensor's filter because it is electrically charged. Some dust, especially larger particles, can be blown off of the sensor with air from a bulb type blower but some cannot. One thing most spot causing contaminants have in common is that the particles are very small. In most cases they are too small to readily see with the unaided eye. A typical digital SLR image sensor has well over 3500 pixels per linear inch, so it does not take a large particle to block light from a few pixels. This is also why even a very small scratch on the sensor cover glass is something to be avoided.

Checking for Sensor Dust

Checking to see whether your sensor needs cleaning is simple enough. The following method works indoors at night, where you will most likely be when cleaning your image sensor. Attach a relatively long lens to the camera, focus the lens manually at infinity, stop it down to its smallest aperture, set the exposure compensation to +1 stop, and photograph any nearby solid white or light colored surface. A laptop screen displaying an all white full screen image works very well, but even a piece of paper or a wall that is reasonably well illuminated will do. The surface being photographed should be no more than a few feet away. The idea is to make the item being photographed extremely out of focus so the only details in the final image will be dust spots and not features of the item being photographed. The small aperture makes the light rays between the back of the lens and image sensor parallel to one another and perpendicular to the glass sensor cover. That causes any dust on the glass cover to cast more distinct shadows on the image sensor. The long focal length makes it possible to assure the image is completely out of focus at the lens's smallest aperture, which would be impossible with a very wide angle lens. The long focal length also makes it possible to use something small and evenly illuminated as a test subject. After this is done view the test image on a computer at 100% (actual pixels) magnification. Just remember to flip the image vertically so everything is oriented properly. What you now see is the maximum possible amount of dust you will see in any normally processed image, with the spots positioned as they are when you look at your image sensor through the camera's lens opening. Unless you just finished cleaning the camera you will always see some, so it is a judgment call as to whether there is enough to warrant cleaning the image sensor. Some use "Auto Levels" in Photoshop to make dust spots stand out even more. I do not because the extreme contrast boost shows spots that would be never be visible in a normally processed image. If I am in the field photographing wildlife I sometimes make an additional exposure as described above, but at a wider aperture like f/8 or f/11. Since wildlife photographs are typically taken using large apertures, this additional test image gives a more realistic idea of whether spots I see in the first test image will show up in the my photos. The smallest spots visible in a test image made at, say, f/32 will be invisible at f/8 or f/11. Likewise, many of those visible at f/8 or f/11 vanish at wider apertures.

I should also mention that I think direct visualization is not the best way to find tiny particles when cleaning an image sensor, which is why I never use it. The method above is easier, provides more magnification, and above all it gives a more realistic idea of what the particles can do to an actual image. That's what really matters.

Getting Carried Away

As with many things it's easy to get carried away and spend a fortune on cleaning tools and magical cleaning solvents. Back in May of 2004 a company called Visible Dust introduced a line of static-chargeable sensor cleaning brushes. They were priced at $34.95 until later the same year when the price suddenly increased to about $100. Visible Dust was using photos of plasma chambers and talk of DNA and biochip technology to sell what was just a simple wood handled brush for an insane price. Really. Today they offer countless pricey high-tech items to help perform the basic low-tech task of cleaning your camera. These include motorized twirling sensor brushes with headlights, no less than five different task-specific solvents and oodles of color-coded task-specific swabs and brushes to go with them, lunar-module-like sensor loupes, and a $50 "Anti Static Property Dust Free Ejection Projectile Free" bulb blower. Holy dust particles Batman! These folks are really cleaning up (pun intended) on the anxiety that exists over cleaning SDLR image sensors. While there is nothing specifically wrong with these products I think they give new meaning to the phrase "marketing hype" and "overkill". A few basic items will keep your images just as spotless for hundreds of dollars less. Specifically, you need a good bulb-type blower, simple but high quality brush, a solvent cleaning tool with pads and a solvent to go with it. All of that will cost about $70, and it's all you will ever need to clean your camera's image sensor.
 

Cleaning with Blowers

Blowing the sensor off with a clean hand operated blower is the safest method, but it can remove only loose dust that is not stuck to the sensor. This cleaning method works well enough to get us by for a few weeks on location, but it does not do a thorough job of cleaning. In addition to not removing any debris that are stuck to the image sensor, it can add or simply move dust around on the sensor unless you do it carefully. It is best to mount the camera on a tripod with the lens opening facing directly downward so particles tend to fall away from the sensor and out of the camera when the sensor is blown off. This position is somewhat awkward, but one gets used to it quickly enough. This method never produces a completely dust -free sensor, but a few small specks on an image are no big deal. Depending on the shooting aperture, they may be completely invisible. In the worst case, cloning them out in Photoshop is quite easy. Given that, if you start out with a clean image sensor there's not much reason to carry more than a blower when traveling, unless you'll be gone for more than a few weeks. It's also a good idea to blow any loose dirt off of your image sensor before cleaning it with any other method. That safely eliminates any larger hard particles that are most likely to scratch. I like the Giottos large (model AA1900) Rocket Air Blower, which can be purchased at many camera outlets including B&H and Adorama for about $8. It's a good idea to keep any blower in a tightly sealed plastic bag so it stays clean.

Cleaning with Solvents a.k.a. Wet Cleaning

This is always, or nearly always, step two in my sensor cleaning regimen. Cleaning with a solvent using what's informally known as the Copper Hill Method removes every spot of every type, including oils. It is also cheap and relatively easy once you learn the technique, though learning it takes a little practice. We have cleaned all of our image sensors this way countless times over nearly a decade and it has never caused even a minor problem. The Copper Hill Method uses a simple tool called the "Sensor Swipe" which can be purchased in a basic kit from Copper Hill Images for $29.95 plus shipping at the time of this writing. The kit contains everything you will need for solvent cleaning and the Copper Hill website has detailed tutorials on the use of these products. Essentially a "QuikStrip" or Pec*Pad is a piece of disposable, lint-free cloth that is attached to the "SensorSwipe" and then moistened with a couple drops of Eclipse solvent. The tool with the moistened cloth attached is then used to clean the camera's image sensor. It's simple enough. Eclipse optical glass cleaner is the key to this process because it leaves absolutely no residue or streaks, and it's the only sensor cleaning solvent you need. Note that the Basic Kit I mentioned comes with your choice of either QuickStrips or Pec*Pads. QuickStrips are like Pec*Pads but made to fit the SensorSwipe. QuickStrips are therefore more compact and convenient than wrapping the larger Pec*Pad multiple times around the SensorSwipe tool. Never cut down a Pec*Pad because cutting will produce tiny pieces of fiber and you are very likely to contaminate the pad with dirt and oil from scissors and fingers in the process.

Eclipse solvent and Pec*Pads are made by Photographic Solutions and can be purchased at Photographic Solutions, Copper Hill Images, Adorama, and elsewhere. The SensorSwipe and QuickStrips are made by Copper Hill Images and as far as I know can be purchased only at Copper Hill Images.

The Copper Hill sensor cleaning method has worked somewhat better for us than the much more expensive Sensor Swab or Sensor Swab Plus, which are both good products produced by Photographic Solutions. This seems to be because the wiping surface is more evenly and firmly supported across its entire width by the Copper Hill Sensor Swipe. The only problem I have encountered with the Copper Hill Method is that the required and flammable Eclipse solvent cannot be transported on commercial airlines. Photographic Solutions may have solved this problem by offering "Digital Survival Kits" that include a 0.5 ounce bottle of Eclipse solvent. Unfortunately the regulations involving carrying things like flammable solvents are not clear. While they seem to exempt quantities of 0.5 ounce and less, the exemptions appear to apply only to things like butane lighters and medical items, not cleaning solvents. Hmmmm.

Solvent Cleaning Product Concerns

You'll notice that Photographic Solutions warns against using Pec*Pads for cleaning image sensors, and that they provide no warranty if Pec*Pads used for this purpose cause damage. They also say that Pec*Pads are safe to use on film emulsion, which is quite soft and scratch prone, mirrors, telescopes, and lenses. The obvious question is why something that will not damage film emulsion, mirrors, telescopes, and lenses might damage the filter over the image sensor in your camera. Fortunately, David Stone of Photographic Solutions took some of his time to explain this to me, and it boils down to two basic facts.

1. The safety of Pec*Pads has not been tested with respect to image sensors, but it has been tested with respect to film emulsions.

2. Cleaning a camera's image sensor requires much more handling of the Pec*Pad than it requires handling of a Sensor Swab, so the risk of contaminating the Pec*Pad with abrasive dirt or oily fingers is much greater. Since Photographic Solutions has no control over how the Pec*Pads are used, they discourage their use for cleaning image sensors.

That's all fair enough. These products are used under all sorts of circumstances by people with various levels of understanding and skill. I would not guarantee the use of either one! I just prefer to assume the risk and save the money, which has not resulted in a single problem over nearly a decade. Sensor Swabs are about $3.75 US each and Sensor Swab Plus is about $5.00 US each while Pec*Pads are only $0.09 US each. Since it often takes more than one of any of these for each cleaning the difference is even bigger than it seems. If you infrequently clean the image sensor on a single camera and doing it stresses you out, the Photographic Solutions Sensor Swabs may make more sense.

To stay out of trouble using the Pec*Pads we always:
1. Work in a clean area.
2. Remove a pad from the factory packaging by gripping its corner with a clean pair of tweezers.
3. We wear new powder-free latex gloves in handling the Pec*Pad. These are available at any drug store.
4. Follow the Copper Hill instructions to the letter, and do not cut or trim the Pec*Pad.
5. Once out of the package, do not let the Pec*Pad touch anything except the sensor until after it is used.
 
Sensor Cleaning Brushes
The principal by which static-chargeable brushes work is simple. Certain materials, like nylon or hair, have a tendency to accumulate a static electrical charge when rubbed against certain other materials, like paper or even air moving at a high speed. The bristles of sensor cleaning brushes are made of such a material. To charge the brush you blow air through it with the same bulb-type blower I already described above. Once charged, the brush is very lightly passed over the surface of the image sensor in your camera. The static charge in the bristles makes any dust particles encountered stick to the brush instead of just being pushed around by it. The only trick involved is to never let the brush bristles touch anything except the sensor. There is oil present in and on the mechanisms surrounding the image sensor and if you get oil on the bristles you'll have a mess on your hands. It's not the end of the world, but it will take a few cleanings with a solvent. also described above, to fix the mess.

Brushes with static-prone bristles and insulating handles have actually been around for as long as there have been brushes. It's possible to source one yourself from a cosmetics shop or artist supply store, but that's not very practical. The brush you end up with might cost only a couple dollars but you'll spend $100 and a lot of time finding the right one. For more detail see this article about sensor cleaning brushes.

The only static-chargeable brush I can recommend is the high quality SensorSweep brush sold by Copper Hill Images for the very sane price of $27.95 plus shipping in August of 2013. They ship quickly and the brush comes with a dust-tight carrying tube and instructions. It's simple, cheap, and effective. Static-chargeable brushes are a handy option that I wouldn't be without, but I use them only for cleaning any dust specks that remain along the edges and corners of an image sensor after wet cleaning. That avoids smearing oily deposits and contaminating the brush. If the Copper Hill SensorSweep seems too low-tech I'd suggest taping it to one of these and naming it the Tropical Caterpillar.

Using a static-chargeable brush to clean your camera's image sensor has potential advantages when it comes to air travel because they are used dry and require no flammable solvents. As I mentioned previously, they are particularly useful for cleaning up the few nits that remain in the sensor's corners and edges after wet cleaning. Static-chargeable brushes alone can remove most or even all particles from an image sensor, and they are not likely to scratch. The real problem with these is that if you brush over an oily particle you will create a large streak. The brush will also be contaminated, making it possible to create more streaks before you realize what happened. If this occurs when there is no way to clean the sensor with solvent you are worse off than if you had not cleaned the sensor at all. Since one can never know when or if this situation will occur I hesitate to use a static-chargeable brushes if there is no access to solvent-based cleaning tools. In fact I use a brush only after a solvent cleaning. That negates the potential air travel advantages of the brushes for me, but it also prevents me from being out in the middle of nowhere with a big streak across my camera's image sensor.

One last thing to remember is that moisture in the air is a good conductor of electricity and it tends to let electrical charges neutralize themselves quickly. Any static-chargeable brush will perform better in dry environments than in humid ones.
 

LensPen SensorKlear

I first used the original LensPen cleaning device long before digital cameras existed. Their performance in cleaning hard to reach rear lens elements and nasty fingerprints from any lens element when you’re out in the field is astonishing. When I found out about the LensPen SensorKlear product for cleaning digital camera image sensors I thought it might be exactly what's needed when air travel is involved because, like the static chargeable brushes it requires no flammable cleaning solvents.

The good news is that the SensorKlear picked up all the particles I saw when I initially checked the sensor at “actual pixels” (100%) in Photoshop, as described previously. The bad news is that it replaced them with loads of extremely fine particles everywhere the SensorKlear had touched the image sensor cover. These could be seen only at “actual pixels” (100%) in Photoshop, and they were smaller and more numerous than I’ve ever seen on my sensor before. These were definitely not present before I used the SensorKlear. I used the SensorKlear again in these areas but it only moved the particles around or added more. After deciding that the SensorKlear was not for me, I used several wet cleanings followed by the Copper Hill brush to get a perfectly clean sensor. I may have been able to do this with only the brush, but I didn’t want to pollute my brush with the extremely fine dust.

I have a few educated guesses about all of this, but I don't intend to do any experimentation to prove or disprove them. First, because checking is done at f/32 with the lens focused at infinity so it's a worst case scenario. The tiny specks might not be seen at all when using more reasonable apertures like f/8 or f/11. Second, even if they were still visible at 100% (actual pixels) in Photoshop they would probably not be visible even in reasonably large prints. In the end the fine particles deposited by the SensorKlear might be too small to matter, but I'm not taking that chance. The usual pieces of crud found on image sensors can be cloned out of an image with relative ease but the particles I found after using the SensorKlear were far too small and numerous to be readily cloned out. I simply don't like the idea of having ultra-fine particles all over my image sensor. I've heard that one can lessen these particles by tapping and gently wiping the SensorKlear cleaning surface on a clean Pec*Pad multiple times to get rid of the excess particles. I'm not going to try this but you are welcome to. I'll even update this article with your results if you let me know. The bottom line is that tiny particles were definitely deposited by the SensorKlear and it's very obvious that other cleaning tools and methods produce a cleaner image sensor.

With all of that said, the particles deposited by the SensorKlear on my image sensor are far too small to matter on a lens element. They would never be seen in a photograph under any circumstance. That's why I will continue using the original LensPen on lenses in hard to reach areas of lenses as needed. Image sensors are a completely different matter and cleanliness there is much more critical.

Just for the record, the LensPen SensorKlear I used was new and used for the first time in the events described here. The camera used was a Canon EOS 1Ds Mark III. I followed all of the directions that came with the SensorKlear and took the same cleanliness precautions I always take with any cleaning method. Those are described above.

Vibrating Self-cleaning Image Sensors

These gizmos may buy some time between manual sensor cleanings but none work well enough to eliminate periodic and thorough manual cleanings. Frankly, cleaning an image sensor isn't difficult enough to justify the complexity and expense of a contraption that works so imperfectly. Because everyone freaks out over the sensor dust issue, Canon and others offer self-cleaning sensors as a marketing tool even though they work poorly and manual cleanings are still required. Of course the marketing literature doesn't say that.

Because these vibrating gizmos cannot possibly remove all of the dust, Canon has also developed software to remove spots created by dust that remains on the sensor. I see this as a rather lame method in principle. One has to take a picture of a plain white surface with the lens focused at infinity to create a dust map so the software knows where the dust is located. But, every time you turn the camera on or off, the vibrating gizmo does its thing, which can move some dust particles and make the dust map inaccurate from the start. Also, any dust that finds its way to the sensor after the dust map is made will not be part of the software's "map". Obviously, a single dust map image cannot work for processing a couple weeks worth of images from a remote location after one arrives home. It will remove some spots, but not all. Further, the size of dust spots in images varies with the aperture used to shoot a given image. Using one test image to remove dust from images shot at varying apertures is a compromise at best. All of this sounds like a lot more hassle than just cleaning the sensor!

Conclusions
When it comes to sensor cleaning it turns out that the simplest and least expensive methods are still the most effective. A good sensor cleaning kit is cheap and it will keep your images just as spot-free as the latest spaceship-inspired whirligig. For a very complete kit I'd suggest a Giottos Large Rocket Blower, a Copper Hill Sensor Sweep brush, a Copper Hill Sensor Swipe with QuickStrips, and a bottle of Eclipse solvent, all for a grand total of about $70 plus shipping. When your camera's image sensor needs cleaning start by blowing it off, follow with a wet cleaning, and finish up the details with the brush. That's what we do and it works like a charm. We typically clean a camera after a two or three weeks of fairly heavy shooting. Between cleaning maintenance can be done with only a blower, but depending on conditions it's not often necessary. If a few spots sneak by they can be easily handled in post processing.

Happy sensor cleaning,

Dean