Everything gets dusty. I know this to be one of the fundamental and immutable laws of physics because I own a house, and everywhere I look I see dust accumulating. On the counter, behind the fridge, even on the cat.
In the same way that your household stuff gets dusty, your digital camera can collect dust as well. If you have a point-and-shoot camera, dust getting inside won't be a problem. But those of you with digital SLRs, be advised: Dust can find its way onto the sensor when you change lenses. This week, let's look at how to remove dust that builds up inside your SLR. We'll emphasize methods that promote cleaning without damaging your equipment. And you'll want to make a point of doing your cleaning in an area that's as dust-free as possible.
Before you worry about the logistics of getting dust out of your camera, it's helpful to know if you really have a problem. Simply put, you know you have dust when you can see the same dark spots in a variety of photos. You can scan your existing photos for telltale dust bunnies, or do it more methodically. Here's how to do that.
Start by setting your camera to its lowest ISO; choosing manual focus mode; and dialing in your lens's smallest aperture setting, such as f/22. Point your camera at a light-colored surface, such as a white wall or a piece of large white poster board, and focus the camera. Since you're shooting with a very small aperture, the shutter speed might be several seconds. If it is, you might want to mount the camera on a tripod. Take a shot. Then reorient the camera. If you took your first picture in landscape mode, for instance, take a second shot in portrait mode.
Now compare the photos, looking at them on your computer screen at 100 percent magnification. Rotate the second picture so it is oriented the same as the first. If you see spots in exactly the same place in both shots, congratulations--you're the proud owner of dust on the sensor. Check out these two photos taken with my own Nikon D200: Example 1, Example 2. Can you spot the dust?
Tools of the Trade
To do the cleaning, you need to get some sensor cleaning gear from your local camera shop.
You'll need a blower--the kind you squeeze to force air through a tube. Be sure that there isn't any sort of brush on the end. And don't use the canned compressed air you might use to clear the dust out of the heatsink on your PC's CPU. The force is too hard and could damage delicate parts.
You should also get a specialized sensor-cleaning brush, which you'll use to sweep the dust off your sensor.
Cleaning Your Camera's Senso
Cleaning your sensor is an understandably scary proposition. If anything goes wrong, you can end up damaging the most sensitive and expensive component of your SLR, requiring a trip to the camera equivalent of the emergency room: the manufacturer's repair center. But as long as you're diligent, careful, and use common sense, cleaning the sensor is little more than a routine maintenance operation.
Start by removing the lens and using the blower to blow loose particles out of the mirror chamber. Keep the camera pointed down so gravity will help get the dust out. Be sure that the blower doesn't come in direct contact with the mirror.
Next, get the mirror out of the way. You'll need to refer to your camera's user guide for details on how to do this. Many Canon cameras, for example, have a sensor cleaning mode, while the some Nikon cameras have a mirror-up control that reveals the sensor. To be on the safe side, do this with your camera connected to AC power, because if the camera turns off because of a low battery, the mirror can snap back in place with no warning, trapping the brush in an ugly disaster.
Now you'll want to use the blower to remove loose dirt, like you just did for the mirror. Use the sensor brush to gently wipe away the more stubborn dirt particles. Check the directions that came with the brush; you'll probably need to "charge" the brush before using it by blowing air through the bristles. Then, gently--very, very gently--sweep the sensor once, recharge the brush, and repeat.
Trust, but Verify
That's all there is to it. Follow your camera manual's instructions to disengage the mirror lockup, and then take a couple of new test shots like we did at the start of this column. Inspect them for signs of dust and, if necessary, clean the sensor again. As long as you are careful about not leaving your sensor exposed to the environment for a long time while you change lenses, though, you should only need to clean your sensor once every six months or so.