Get rid of sensor dust safely and save a bundle!
You can save a bundle and do a better job removing sensor dust by cleaning your digital camera's sensor yourself! Here's a an effective sensor cleaning method.
You can't rely on new technology to assure you of a clean digital camera sensor. Many interchangeable lens cameras—DSLRs and MILCs—made in recent years have self-cleaning sensors that vibrate at ultrasonic speeds when the camera is turned on and off. This may help shake some of the dirt loose, but it doesn't replace cleaning for a clean digital camera sensor. With self-cleaning sensors, you may not need to clean them as often, but you still need to clean them. You can find a lot of information online and elsewhere about how to clean a sensor, but I believe my sensor cleaning method is more thorough than any others I have seen.
Even with self-cleaning, sensor spots are actually more of an issue today them they were a few years ago. Image manipulations such as HDR or the tone mapping-like contrast increases, including those in many popular filters such as those from Nik and Topaz, will show spots that you didn’t notice before.
There’s a lot of debate about do-it-yourself vs. sending it out. I want to be able to clean my sensor when it needs it, which can be at inconvenient times, and to have it done quickly. And, frankly, I think I’ll do a better job than anyone else. Cleaning a sensor can be tedious. Sometimes it gets worse before it gets better, and I’ll stay at it until it’s done to my satisfaction.
There is always the potential of doing damage when you’re working in the sensor chamber, but every time you pick your camera up, there’s a danger of dropping it. If you take a few basic precautions and exercise reasonable care, the potential for damage is small.
How to do a sensor check
Even if you don’t want to try cleaning it yourself, it’s easy to find out how dirty the sensor is by shooting a clear sky or a clean, smooth piece of paper. (When I’m out shooting, I’ll turn a clear sky into an advantage by shooting a sensor check. It will give me an idea what I’ll need to clone out on the images, as well as how badly I need to clean the sensor.)
Here’s how to shoot a check image:
- Set your lowest “normal range” ISO (100 for Canon, and 200 for Nikon). Don’t set a lower ISO that is in the “extended range.” You’ll get the lowest noise at your lowest normal ISO.
- You want the shot to be out of focus, so set manual focus and focus to infinity for a piece of paper and close-focus for the sky.
- Set f/22, so any spots will be well defined. At a wider aperture such as f/5.6 they may not show, and at a smaller aperture such as f/32 you may see too much detail. (The spots are shadows of stuff that is on a glass surface in front of the sensor itself.)
- If you’re shooting a piece of paper indoors, you’ll have a slow shutter speed. That’s fine; you want to blur the subject as much as possible anyway, so go ahead and hand hold. You just want to shoot featureless light.
- You want a somewhat telephoto focal length in order to shoot a small segment of the target, in order to minimize any tonal gradients. It depends on the evenness of the illumination of your target, of course, but 70-100 mm is usually fine.
- If you’re a JPEG shooter, that’s OK, but make sure you’re using the highest quality and largest file size. (I would hope you are anyway.)
Post Process to find the spots
Now here’s what to do with the test image. (Just looking at it on the back of the camera will only show up the really awful spots.) Open it on the computer and desaturate it, either in the RAW converter or in Photoshop. You might see some spots at this point, but to really see what’s there, make a Levels adjustment layer above your Background image. Go to Layer > New Adjustment Layer > Levels, or use the black and white circle icon at the bottom of the Layers panel / palette.
In the Layer adjustment, the narrowness of the histogram peak will indicate how much tonal gradient you have captured. The narrower, the better but no need to get it super narrow. Increase contrast by bringing in the two end sliders to meet the ends of the peak and you will really see what’s on the sensor. You will also see some darkening in the corners due to normal light falloff in the lens.
Here you can see a piece of lint bottom center and a spot on the left. There are many more spots that you can’t see in this small web image.
The image a lens projects onto the sensor is upside-down, and when the camera processes the image it is flipped right side up. So the image of the sensor you see has been flipped and the piece of lint is actually at the top of the sensor
Seeing something like this, you know you need to clean. Find the item in your camera menu that flips up the mirror and lets you access the sensor. But first, make sure you have a fully charged battery. If the battery runs down while you’re working in the sensor chamber, the mirror will slap down and you will have a very expensive repair. The same goes for inadvertently nudging the card door enough to “open” it. Lay the camera down on a table instead of holding it. Don’t touch anything as you clean.
When I see large dust pieces like this, I start the cleaning process by blowing on the sensor with an air bulb such as the Giottos Rocket Air Blaster. (To do this, I can safely hold the camera and turn it upside down because the bulb tip needn’t be inside the chamber. Never use canned air; the propellant can put a residue on the sensor that will probably need professional removal. Large pieces will often blow off and fall out of the chamber.
Actually, I’ll blow on the mirror before I put it up. And I’ll blow off the back of the lens, too. There’s so much dust everywhere, I might as well get rid of whatever I can. The sensor has an electrostatic charge when the camera is on in its normal mode (but not in sensor-cleaning mode) and it will attract dust like a magnet.
At this point, I find a sensor scope very handy. It’s a magnifying glass with a light shining on the sensor. (I like the Delkin Sensor Scope.) You’ll see spots like the above as tiny silver threads or spots. I’ll repeat the air bulb and sensor scope check until I have gotten what I can, and then shoot a piece of paper to see if I had any luck blowing off some of the smaller spots. Usually the answer is no.
Then I’ll go after the smaller spots that I can only see on the Photoshop image. They may look much less significant but they will show up when you do many image manipulations. You’ll want to zoom into the image to see these smaller spots. Here’s a 50% zoom of the above sensor image. This is Not a Good Thing.
The smallest and lightest spots aren’t of much significance, but the others are. So the next step is to try a sensor-cleaning brush. These are very special brushes whose bristles hold an electrostatic charge and attract particles off the sensor, rather than “sweeping” them off, so a light touch is needed. These brushes need to be kept very clean. You charge them right before use by blowing on the bristles with a squeeze bulb or by spinning the bristles with the battery-powered Visible Dust Arctic Butterfly. (Do not spin it while it is in the sensor chamber.)
Often brushing won’t get all the spots and you’ll need to resort to swabs and solvents. After brushing you’ll need to repeat the shot of the sky or a piece of paper, and if you see an elongated smear, you’ve brushed through an oil spot thrown by the shutter. In this case you’ll need to clean the brush in its recommended manner before using it again, and you’ll need to resort to solvents to remove the oil.
There are several manufacturers of sensor cleaning supplies and I haven’t tried them all. I use the products from Visible Dust but I can’t claim they are better than any others. I use the Arctic Butterfly brush, the green swabs, and Sensor Clean and Smear Away solvents. There is information on manufacturer’s web site about sensor cleaning and proper use of their products. And the solvents (or at least some of them) are said to leave a coating on the sensor that helps repel future dust.
Read the product directions very carefully. The swabs should be kept very clean and should be carefully moistened right on the edge, with two drops of solvent, each one placed one-fourth of the way in from the edge, in order to evenly wet the edge. Let the solvent soak in a minute or so before swabbing. You don’t want to squeeze out liquid on the sensor glass.
I tilt the swab and drag it in one pass from one edge of the sensor to the other, and then turn it over and drag it back the other way, so the other side of the edge is being used. (Check manufacturer’s web sites for video demonstrations.) You will need some pressure with the swab, unlike the brush.
If I see an oil smear I use the Smear Away solvent, which needs to be followed by the Sensor Clean solvent. The swabs may leave lint, so another loupe inspection is in order, followed by the blower and if, needed, the brush. (I have two, so if I brush through oil I can continue cleaning.)
If there is no oil smear I just use Sensor Clean. Regardless of the solvent, it may take several passes, each with a clean swab, to get everything clean. And junk may be pulled in from the edges of the sensor making things worse before they get better. But they will get better.
At the stage where I can no longer see any dust or spots with the loupe, I repeat a sensor check by shooting the piece of plain paper again. It may take several repetitions to get things clean, but I think it’s worth the trouble.
There is another Visible Dust solvent that I can’t recommend: VDust. I’m not in the business of cleaning sensors, but of the few I’ve done for friends, I’ve cleaned two that showed a very strange look when the contrast was increased with Levels, as if there was a liquid on the surface that didn’t “wet” it. In my first experience with this product, I used the person’s cleaning kit, which included the VDust solvent. In the second case, when I did an initial Levels check I saw that same look and found the person had been using VDust, according to directions, and the sensor had been in this condition for many weeks. In both cases I used Sensor Clean and managed to get the residue off, but it took many passes with clean swabs each time. I have no idea what is going on here. After the first incident, I emailed the company but they were not interested in my experience and insisted the product was fine.
Sometimes you will see a much larger and dimmer spot on the sensor. Mine are always hexagonal, reflecting the aperture leaves in the lens. These are not on the sensor but are bits of dust or dirt on the lens, either the front or rear surfaces.
It’s very important to keep the rear element of the lens and the sensor loupe clean as dust can jump or fall from them onto the sensor.
There are also products to clean the walls of the sensor chamber. Although there’s no easy way to assess their effectiveness, I’m in favor of keeping things as clean as I can.
In conclusion, the cleaning process can be tedious. But how much confidence do you have that if you send your camera out to be cleaned, it will be done with sufficient attention to detail? At least, now you have a means to check it after the fact.