As we enter the adolescence of the digital camera age after spending the last 10 years in childhood, one of the biggest weaknesses of digital imaging with DSLRs is finally starting to be addressed by the camera manufacturers. This weakness is sensor contamination, which results in undesired spots on photographs due dirt blocking light from properly illuminating the pixel sites beneath the dirt. More correctly, it is the filter in front of the sensor that is getting contaminated. This contamination can be from many sources including dust particles, particles shed by the camera through its mechanical motions, particles left over from the manufacturing process that have found its way to the sensor, lubricants used in the building of the camera, environmental contamination, human skin flakes, body and lens cap plastic shards or any of a myriad of other sources.
Over the years many established and start-up companies have offered solutions for the various types of dirt that can foul the sensor filter. Unfortunately none of them addresses all types of sensor contamination in an optimal way. Each solution tends to be very good at one or two types of contamination but not so good for others. This article will describe many of the sensor cleaning methods available today including their pros and cons. It is not designed to be a tutorial for how to optimally use each sensor cleaning method. The instructions included with these products are the best source for properly using sensor-cleaning products. The terms sensor filter and sensor are used interchangeably in this article and all refer to the protective filter that is mounted in front of the actual CMOS or CCD sensor.
The Camera Manufacturers
The manufacturers’ solutions are all variations on the same theme. Typically these include four elements.
- First, an anti-static coating or anti-static ionizing system is employed on or near the sensor. This tries to neutralize charge build up on the sensor filter, which in turn reduces the chance for the sensor to attract dust that is then locked in place due to electrostatic force.
- Second, some sort of shaker for the filter element that sits in front of the sensor. This can use mechanical shaking or ultrasonic waves being passed through the sensor filter to shake off particles.
- Third, a trap for the shaken off particles so that they don’t just redeposit themselves on the sensor at a later time. This is typically done with a sticky area around the frame of the sensor.
- Finally, there is often a software driven system to map out particulate and replace the image data at pixel locations that have been affected by dirt, using data from surrounding pixels.
It is very easy to see what the strengths of this system are. It goes after the particulate that is generated inside and out of the camera that finds its way to the sensor. This sort of system is generally very effective at shaking off the dust. However, it does not address what I will refer to as “gunk.” Gunk consists of anything that is not a solid particle and can include lubricants or anything that has a liquid component. It also cannot address gaseous contamination that has condensed on the sensor leaving behind a film. Another potential weakness of this system, which has not been borne out as yet but may become an issue as these cameras age, is the sticky frame – what happens to it as it dries out over the years, does it start to shed particles? How often should it be replaced? How long does it take for a sticky frame to get “loaded up” with contamination in dusty environments?
The Blower Bulb
The blower bulb is simply a rubber vessel that takes in air from the atmosphere and discharges it in a concentrated stream through a nozzle. These air blowers can be effective in blowing dust off of the sensor filter surface; however, they also carry a lot of negatives with them. They are exceptional at moving air around but with that they also move all of the contaminants in the air such as dust, moisture, and lint, sending them onto the sensor. Not only that, often they can shed their own particulate from the rubber and nozzle which could end up on the sensor. For this reason it is imperative that the rubber bulb is pristine, moisture free and used in a very low dust environment. Blower bulbs also are only marginally effective at moving particles that are stuck on by strong electrostatic forces, through liquid surface tension or cemented on due to the drying of moisture around the particle.
Firefly makes a new variation on the blower bulb that conditions the air. It puts a filtration and charge neutralizer on the nozzle. The idea is to provide a clean stream of air while deionizing the sensor surface so that particles can be easily blown off. This sounds like a great idea but it still will not address gunk or cemented particles.
An alternative to the blower bulb is compressed canned air. It is generally not recommended due to the byproducts that are delivered with the stream; however, the power of the blast can dislodge some stubborn particles. To use this method, place the can on a table top and allow the initial burst to go into open air thereby expending most of the byproducts into the air. Without moving the can, then place the camera in front of the compressed air stream. Also note that this definitely causes thermal shock to the sensor filter due to the extremely cold temperature.
Shortly after DSLRs hit the mainstream with the Nikon D1 and Canon EOS D30, the wet cleaning method became very popular. It was essentially the only game in town for sensor cleaning. This method uses an alcohol based cleaner and a lint free pad to clean contamination off the sensor. Photographic Solutions markets a solution called Eclipse that has the largest market share among wet cleaners. Note that there are two different formulations based on the type of manufacturing process used for the sensor (see www.photosol.com). Photographic Solutions also markets a line of Sensor Swabs, which is essentially a properly sized PecPad on a plastic stick for various sized sensors. These are assembled and packaged in a clean room to insure a low level of contamination. Unfortunately the sensor swabs are very expensive and are used just once; often it takes 2 or 3 swabs for a badly contaminated sensor. Whenever something costs too much, people will look to devise their own; many simply purchase the PecPad material and style their own sensor swab most often with cut to size rubber spatulas.
The wet cleaning method is very effective at removing gunk. It is probably the best way to remove lubricant or condensation induced contamination. One must be careful not to use too much of the cleaning liquid to insure no liquid is left on the sensor, which then causes steaks. On the other hand this method is only somewhat effective at removing particulate. It often just pushes the particles around and especially on full frame sensors tends to push particles into the corners of the frame where they are very difficult to remove. For this reason it is a good idea to use the blower bulb method (or the tacky surface approach covered later) prior to wet cleaning. The high cost makes this method desirable only for stuck on or gunk type of contamination.
Several companies offer variations on the static brush theme. This method electrostatically charges a brush in the opposite polarity of the charge that sensors generally acquire. When the brush touches the sensor, not only does it neutralize the charge on the sensor surface, it also then attracts the dust particles off of the sensor and onto the brush, thereby removing the particulate. Prior to actually cleaning the sensor, one must first charge the brush. Different systems for this are available including charging the brush with a high energy burst of air, rubbing the brush on a material designed to create a charge (similar to rubbing a balloon on curtains to induce a static charge so that they stick to walls), or spinning the brush with a motor that charges the brush through the induced friction with the air. All of these methods aim to accomplish the same thing – charge the brush so that it attracts dust.
The static brush method is effective at electrostatically sucking particles off of the sensor, but it is actually counterproductive on gunk contamination as it will just spread it around and thereby also contaminate the brush. Also, as soon as the brush is charging it is also attracting particles out of the air, causing contamination to the brush. To be useful, the brush must be kept impeccably clean.
Another class of lens cleaning products is what I will call sensor polishers. The most common of these is the LensPen Sensor Clear product. Originally developed to remove stubborn contamination from lens surfaces, LensPen has adapted the product as a sensor cleaner by making the polishing surface of the LensPen smaller and angular so that one can get into the corners of the sensor. The basic premise here is to attack all types of sensor contamination by polishing it off with a gentle polishing tip.
The sensor polishers are perhaps the most effective at removing stubborn corner dust and residue left behind by wet cleaning with too much liquid. However, they also have the tendency to push dirt around a bit. While they can usually pick up most dust, there is the risk of scratching the sensor if there is a large or sharp-edged particle on the sensor. The biggest drawback to this method is that, in theory, each pen should only be used once; at a cost of $10 per pen, this would be very expensive.
Vacuum systems use the carpet cleaner mentality—put something that sucks air in the proximity of the dirt and try to suck it off of the sensor. While this may sound like a great idea, it is perhaps one of the least effective methods of cleaning as it does nothing to eliminate static charge and in all likelihood will increase static on the sensor due to air moving in a constant stream across the sensor surface. One also runs the risk of sucking dirt onto the sensor that wasn’t there to begin with. The vacuum also generally will not remove dirt that is cemented to the sensor, nor will it do anything for gunk.
Adhesive Contact Cleaners
A relative latecomer to the sensor cleaning arena, but one that can be very effective, is the adhesive pad. DustAid is the leader in this method. Basically it uses a low tack and zero residue tape on a pad. One puts the pad in contact with the sensor and then in a rocking motion peels it back off, taking contamination off the sensor. Depending on the type of sensor filter a camera has, there are different tackiness levels – one must choose the right level to insure that the sticky surface will come off the sensor without leaving anything behind or damaging the coatings of the filter.
This method is perhaps the most effective way of removing particulate and it is also very effective at removing even cemented-on contamination. It isn’t 100% effective at removing gunk but is still more effective than most other cleaning methods that target particulate. Its drawbacks are cost at about $4 per cleaning; often a pad is wasted because it doesn’t come off of its backing film cleanly.
There may be other commercial or homebrewed methods out there, but the major systems available have been reviewed above. By now it will have become clear that no single solution will address every situation and that different methods will be most effective depending on the contamination type that is ailing a sensor.
Most photographers serious about the cleanliness of their sensors will want to have at least one method that is exceptional at particle removal and another that is exceptional at gunk removal. When gunk is the diagnosis, always do a particle clean prior to doing the gunk removal since gunk removal always involves direct contact with the sensor filter. By removing particles first one reduces the chance of scratching the sensor or pushing the particulate around.
In closing, my cleaning system consists of blower bulbs, compressed air, Eclipse with Sensor Swabs for serious gunk removal and the DustAid adhesive system for particle removal. All the products described in this article are available in the NatureScapes.net store.