dSLR Sensor Cleaning
You've been taking great shots with your dSLR for some time, changing lenses for the occasion, and now you notice some spots in your photos in bright areas like blue skies. The spots seem to be in the same place in the frame with each shot. Then a sinking feeling of doom ensues as you realize you have dust in the camera and visions of opening the camera and electronic microsurgery enter your mind. Sensor cleaning can seem beyond the ability of the average dSLR owner but the procedure really isn't very difficult. It all comes down to your ability to follow instructions in most cases. Let's take a look at sensor dust and sensor cleaning to see if it is something you would like to try or if you'd rather take the camera to your local camera shop instead.
Recognizing dust and debris
Above are two examples of dust in the camera. Dust can appear as near-pinpoint specs (top crop) or more diffuse/larger circles (bottom crop). The above is a relatively mild case of dust and you may see other types of debris such as much larger or darker spots, small hairs, and so on. Dust is more visible in areas of bright, uniform color such as blue skies. In addition, due to the angle of light and the shadow created on the sensor by the dust, the dust often appears more diffuse at larger apertures and closer to small specs at small apertures. Most importantly, the specs or circles will be in the same place in each frame.
If you see spots like those above in your photos and suspect dust in the camera, the first logical step is to go to an environment that is relatively dust free, remove the lens, and carefully clean both the front and rear glass elements on the lens. If spots still appear after cleaning the lens, you'll know the dust is on the sensor. Next, set your camera to aperture priority and select a very small aperture like f/22. Set the camera to the lowest ISO setting such as ISO 100. Now find a uniform surface like a white ceiling or wall in a well lit room. It is more important that the surface be as uniform and texture-free as possible than the surface being white: any light color will do. Take a shot of the wall/ceiling. Note that if the camera picks an exposure time of one second or longer, this is a good thing! In fact, the more you move the camera (within the bounds of the uniform wall/ceiling), and the longer the exposure the better, because we want to blur any non uniformity on the wall/ceiling: the dust on the sensor won't move so it will still be sharp. Be sure to open the shot in your favorite photo viewing/editing tool and move around the shot at 100% (1:1) zoom so you can see the small specs if they exist.
It's confirmed: you have dust on the sensor
Now that you've cleaned the lens elements and have identified some spots in the frame, you want to clean the sensor to remove the debris. I like to approach sensor cleaning in stages, performing the least invasive cleaning first and working up to the tougher cleaning techniques. The first method of cleaning is to use a simple handheld blower bulb. These are the little rubber bulbs with a little plastic tube that you can buy at almost any camera store. While various forms of canned compressed air can blow more air, you're safer using a simple squeeze bulb as some canned air products can contain oil or may spray liquid (read very cold) gas which can harm the sensor or at least make your cleaning job even more difficult by spraying a residue onto the sensor.
Before beginning any sensor cleaning task, first make sure your camera battery is fully charged. You don't want the shutter/mirror closing on you while you are cleaning! While most cameras offer a "sensor clean" or "mirror up" function in the menu that was designed for cleaning, some (particularly older) cameras don't offer this feature or only offer the feature if you have an AC power supply. In those cases, you can usually set the camera to manual exposure and set the shutter to 30 seconds. You then have about 20 seconds to do your cleaning once you press the shutter release (you don't want to come anywhere near the 30 seconds and risk the mirror/shutter closing so getting out of there by 15-20 seconds seems prudent). I prefer using the 30 second shutter instead of the bulb setting for cleaning when a specific cleaning option isn't present in the menus because: (a) you know how long you have before you have to remove the cleaning devices and (b) if you use the bulb setting, your finger may slip off the shutter button while you are cleaning.
Obviously, remove the lens from the mount first and then open the shutter so that you can see the sensor in the camera. My preference is to hold the camera so that the lens mount is facing the floor. That way, any debris that is blown out has a better chance of falling out onto the floor instead of just being blown around in the camera. With the camera facing down and the shutter open, put the tube of the bulb blower up to the lens mount and center it in the middle of the hole. I would recommend not putting the tube into the lens mount hole or close to the sensor because when you squeeze the bulb, there is a chance that the movement will cause the tube to strike something (mirror, shutter, or even sensor) in the camera. So keep the tube just outside the lens mount hole. Give a few quick bursts of air pointing the tube at the middle of the sensor. Once you've done that, take another test shot (per the above instructions). Did the dust specs go away?
If most of the dust specs went away with only one or two very small specs left, you've probably done a good enough job. You may want to repeat the bulb cleaning per the above one or two more times to see if you can get all the dust removed but for the average Joe, be happy with only a spec or two! Many times people go too far with different techniques and end up making it worse and/or inserting more debris into the system. Also realize that the smaller specs are only likely to show up in "sky shots" using a very small aperture anyway.
A more thorough cleaning
So what if the simple blower bulb method doesn't work? Maybe some of the specs on your sensor are "sticky" and will not come off with a simple shot of air. There are many products on the market such as fine brushes, mild solvents w/swabs, and even "sticky tape" products designed to clean more stubborn debris from the sensor. Again, my preference is to go with the lighter touch first. In my opinion, the next phase is to try a sensor cleaning brush. A Canadian company called Visible Dust makes good products that I have used on a number of cameras. One Visible Dust product that I can recommend is the Arctic Butterfly. The Arctic Butterfly is basically a very fine bristle brush on a rotating shaft. You simply press a button for a few seconds and the brush rotates in the air rapidly (the unit is battery powered), flinging off any prior dust that might have been on the brush while statically charging the brush at the same time. Once charged, you simply lightly swipe the brush over the sensor (never spin the brush while it is in the camera) and recheck for dust specs.
I find that a quick swipe with the Arctic Butterfly followed by a burst or two from the blower bulb often leads to the best results since it can be difficult to get the dust off the edge of the sensor sometimes and the static charge doesn't always attract all the dust. If the brush method is still unable to remove those last few specs, you may need a "wet cleaning". Visible Dust also sells swabs and cleaning solution. A wet cleaning, your last resort to cleaning, basically consists of wetting a swab with cleaning solution and swiping the sensor with the swab. As with any method, the most important part of the task is to follow the instructions explicitly! Sensor cleaning at its worst, comes down to nothing more than a window cleaning job... a delicate one... and one done in a confined space. Other than following directions, the best advice I can give is to first determine if you are up to the task after reading this article and possibly even the online instructions: Visible Dust has detailed illustrated instructions on their web site for example. If you feel confident enough about taking on the challenge, just be gentle! While sensors are more protected by things like antialiasing filters than most people might think, care is still needed to avoid damage to your camera. Whatever cleaning method you choose, follow instructions, take your time, and be sure that the mirror/shutter never closes while you are doing things like brushing the sensor! Shutter/mirror damage is actually more common than damage to the actual sensor.
But my camera has electronic sensor cleaning
Many newer dSLR's employ a method of electronic sensor cleaning where the camera basically shakes the sensor at ultrasonic (fast) frequencies to dislodge debris from the sensor. While this feature is great to have and it does work (albeit the effectiveness varies widely across manufacturers and camera models), I'm not a big fan of electronic sensor cleaning. When the electronic sensor cleaning cycle is done and that dust is gone from the sensor, where did it go? You guessed it: somewhere inside the camera, and if all you ever did was perform electronic cleaning cycles, some of that dislodged dust is likely to make its way back onto the sensor eventually. On cameras that will allow you to run the electronic cleaning cycle with the lens removed and the shutter open, I like to hold the camera with the lens off, shutter open, camera mount facing the floor, and then run the cleaning cycle. If you do this in a room where the air is still, most of the debris will fall straight out the camera mount hole and onto the floor instead of being dislodged into the inside of your camera. In any case, even with electronic cleaning devices, it is inevitable that eventually, you'll need to manually clean your camera's sensor as the electronic cleaning cycles cannot remove all (types of) debris. Self cleaning ovens are nice too, but it doesn't mean you'll never have to wipe the inside of your oven. The same goes for electronic sensor cleaning. If the electronic cleaning cycle doesn't remove all the dust specs, don't get discouraged. Just realize that such devices cannot completely eliminate the need for an occasional sensor cleaning.
For those who shoot with dSLR cameras, sensor cleaning will eventually become a fact of life; a part of normal maintenance for your camera. If you're skittish about technical things, it might be best to take your camera to the local camera store when a cleaning is needed. If you are not intimidated by the occasional techie type job, however, sensor cleaning might be worth a try. In my opinion, it is certainly something achievable by the average person as long as care is taken and instructions are followed to the letter. In addition, starting from the simplest cleaning method first (the blower bulb method) and working your way up, perhaps you can get a better idea about the type of cleaning you are capable of performing without jumping in the deep end first and then finding that you can't swim!