In my last Framed and Exposed, I addressed the problem of digital camera sensor dust. If you have a point-and-shoot camera, you don’t have to worry about sensor dust, because your camera is completely sealed. But if you use a digital SLR, you might one day find your images exhibiting annoying smears and spots. Because the lenses on most SLRs are removable, dust and who knows what else can work its way inside your camera and stick to the sensor. Even if you never remove the lens, it’s still theoretically possible for dust to get on your sensor, particularly if you shoot in dry dusty environments.
Last time, we looked at methods for preventing sensor dust and how to work around it when it does occur. In addition to shooting at wider apertures to reduce sensor dust visibility, I mentioned simple cleaning techniques that can lessen the chance you’ll develop a dust problem.
However, no matter how careful you are, one day you might download pictures from your camera and find spots and smudges. If the spots aren’t bad, you can try to remove them with an image editor’s rubber stamp or clone tool. If you shoot lots of images, though, or if the dust problem is severe, a manual fix isn’t practical. You need to clean your camera’s sensor.
Not for the Faint of Warranty
Your camera’s sensor sits directly behind the lens, inside a chamber that houses a mirror. When you press the shutter release, this mirror flips upward to reveal the shutter. The shutter then opens to expose the sensor.
The image sensor chip is not directly exposed (pun intended) but sits behind a protective covering. The distance between the covering and the chip often has a lot to do with how visible dust can be. When the sensor and cover are very close together, dust will be more visible than when the protective cover is far away from the sensor.
The good news is that, because of this configuration, you’re not actually cleaning the sensor, but its protective covering. The bad news is, scratching or damaging this covering still messes up your camera.
For this reason, many manufacturers cite cleaning your camera as a violation of your warranty. If you don’t want to lose your warranty’s protection, are extremely uncoordinated, or generally have perpetual bad luck, cleaning your sensor yourself may not be the best idea.
But if you’re up for the challenge, you’ll be relieved to hear that sensor cleaning is a relatively easy process. You have to work pretty hard to damage your camera, so there’s really no reason to be afraid of trying it.
Is it Really Dirty?
Some smudges and blobs might be debris on your camera lens (or on your computer screen; I’ve spent an embarrassing amount of time trying to clone away spots that turned out to be dirt on my monitor). Though you can clean your lenses to see if this takes care of the problem, the best way to determine if your camera sensor needs a cleaning is to shoot a picture of its dust, if there is any.
First, select a lens with a short to normal focal length (20-50mm). Clean the lens and then put it on your camera. Switch to aperture priority mode and choose a very small aperture, such as f/22. Set your lens to manual focus and point the camera at a featureless blue sky, or at a bare white wall. You don’t want to confuse any image detail for sensor dust, so try to get the lens as out of focus as possible. You can even set to a slow shutter speed and move the camera around a bit while shooting to further blur any detail. If you’re shooting the sky, shoot as straight up as possible, to avoid the brightening of the sky that appears toward the horizon. Obviously, point as far away from the sun as you can. Shoot a couple of frames and then import them into your computer.
If you have any dust problems, they should be easily visible, such as the image below.
Shooting at a color field with an extremely small aperture makes it simple to see any sensor dust problems that your camera might be experiencing.
There’s dust, and then there’s dust. Shooting soft focus with an extremely narrow aperture at a bare field of color is going to reveal even tiny dust issues that will probably be invisible in most shooting situations. Once you’ve shot this “dust map,” look at your other recent images to see whether any of the dust that you can see in your test image is visible in other images. If it’s not, you might not want to risk cleaning your sensor. If it is, or if your dust problems include black spots and heavy smudges, you’ll want to clean.
If your camera is new but has dust problems, some may come from the camera itself. As you use it, particles can slough off of different components inside the mirror chamber. Over time, this particle shedding will wane, but in the meantime you might still need to do a cleaning.
First, the Air
In my last article, I explained how to use air blowers from a camera store — or embarrassing items from a drug store — to clean the inside of the camera. I also mentioned that you should never used canned compressed air for cleaning the inside of the your camera.
For sensor cleaning, continue to stay far away from compressed air. Make your first cleaning attempt with a normal blower.
Find a non-drafty, well-lit, clean location and get your blower or blower brush. Next, remove the camera’s lens, and you’ll see the mirror that sits between you and the cleaning you want to do. Blow out the sensor chamber so there aren’t any particles to fall on the sensor. You’re now ready to start the cleaning in earnest.
Most SLRs have a special cleaning mode that flips up the mirror, opens the shutter, and leaves them both that way until the camera is powered down. With the shutter and mirror out of the way, you’ll be able to get to the sensor.
This is the potentially risky part. If the camera loses power, the shutter will close and the mirror will come down. If you’ve got the tip of a blower brush in the way of the shutter or mirror when they try to close, you could seriously damage the mechanics of your camera. Consequently, you want to ensure that you have a completely charged battery installed before you start cleaning. If you have an AC adapter for your camera, that’s even better. Some cameras, such as Nikon SLRs, don’t let you activate cleaning mode unless they’re powered by AC.
If your camera requires an external power supply for cleaning (something that usually costs a fair amount) then you might think it clever to throw the camera into Bulb mode, which leaves the shutter and mirror aside for as long as you hold the shutter release. This is a bad idea. First, no matter how careful you are, you might let go of the shutter release. Even if you have a remote with a lockable shutter release, it’s still a bad idea because the camera will actually be taking a picture, meaning its sensor will be charged with a potentially dust-attracting electrical charge.
Cleaning mode is usually activated using a function on the camera’s main menuing system. In some cases it may be a custom function or buried deep in a sub-menu to prevent accidental activation. Before starting to clean, read your camera’s manual for full instructions on how to use the cleaning mode.
When blowing out the sensor chamber, hold the camera down so that any dust you dislodge will fall out of the camera. Once you’ve activated cleaning mode, place the tip of your blower just inside the camera. Don’t place it right on top of the sensor, as doing so will increase the chances that you’ll bump the protective glass plate — a very bad scenario. And you definitely don’t want to brush the sensor with a blower brush. As long as the blower is big enough, inserting it just past the camera mount should give you enough cleaning power.
Give a few vigorous blowings, then cancel cleaning mode.
Now, remount your lens and perform your dust test again. Did you eliminate the problem? If not, you’ll have to take more drastic measures.
When air cleaning isn’t enough, you need special cleaning tools. A combination of special brushes and cleaning solutions, these cleaning techniques involve brushing or swabbing the actual sensor covering. This involves manipulating the most sensitive part of your camera’s imaging mechanism, so it’s a good time to re-assess whether you want to send your camera to the manufacturer for cleaning.
DO NOT use your own brushes or cleaning solutions for cleaning your sensor! Cleaning your sensor requires brush hygiene of a completely different order of magnitude. Unfortunately, it’s an order of magnitude that will cost you some money.
Visible Dust, Inc., has a long history of developing products for cleaning high-end optical devices such as microscopes. They now offer product kits for cleaning digital image sensors. These kits range from special brushes, to cleaning solutions and swabs, to combinations of both. I recommend them.
In addition to selling cleaning kits, Visible Dust also provides detailed cleaning instructions.
Ashes to Ashes…
Depending on your shooting habits and proclivities, you may never have a dust problem, or you may encounter it only once every few years. The first cleaning will be the hardest, simply because it can be a little scary to muck with the guts of your camera. However, it is possible to effectively clean your own camera sensor without damaging your gear.