Let's talk about dust
One of the biggest concerns for many people contemplating buying a DSLR is dust. “Back in the film days” every time you took a picture you effectively got a new sensor. Even if a ridiculous amount of dust got stuck to it, the worst that could happen was you ruined one picture. Wind on the film and clean the “sensor”. Now it's a bit more complicated - a DSLR uses the same sensor for its entire life. Even worse, the sensor is statically charged so it's going to attract dust and any dust on it will pretty much stay there until you remove it. In this feature I'm going to look at dust, what to do to remove it and what not to do.
First a warning
I checked the official advice from Nikon, Canon and Sony. The party line from all three is “don't touch the sensor - ever”. They all advise using hand air blowers to remove loose dust. Many users have found this impractical and that they simply can't shift stubborn dust this way. In this article we will look at other methods. None of these methods is recommended or endorsed by ThinkCamera. We are reporting what others have found to work - not advising you to do the same. If you are in any way worried about cleaning your sensor then leave it to the experts (details below) and remember that touching the sensor with anything could invalidate your warranty.
Where does dust come from?
A popular misconception is that dust comes in from the air (environmental dust). Many people believe that by keeping one lens on the camera all the time they will avoid dust contamination. This will certainly limit the amount of dust but it also comes from other sources. Much of the dust you see on a sensor will come either from manufacturing residue (it's there before the camera is assembled) and some is created by the camera itself (yep, your camera is literally wearing itself to pieces). These last two sources go some way to explaining why a new DSLR tends to have more dust than an old one.
Recently camera manufacturers have taken note of this and taken steps to prevent both residue dust and camera generated dust. Components are now being chosen that don't degrade in a way that produces dust. There are also efforts to make sure that little residue is left in a camera when it is assembled and that any that is there is trapped by special dust trap areas.
The 4 step plan
Here's how I deal with dust in my camera. I use 4 separate steps to decide how much cleaning is required.
Check
| First of all check if your sensor needs cleaning. Cleaning a sensor will take time, may cost you money and could destroy your camera - let's not do it more than we have to. People often look through viewfinders and worry because they see dust which doesn't appear on pictures. There are two optical paths in a camera - the seeing path and the taking path. The seeing path goes from the front to the back of the lens, off the mirror, through the pentaprism and out of the eyepiece. The taking path again starts with the lens but when the shutter opens the mirror springs up and the sensor is exposed. Rule of thumb: if you can see dust when you hold the camera to your eye then it's in the seeing path. Unless it's on the lens the only worry with dust like this is that it might migrate to the sensor. If you can't see dust in the pictures then don't worry about it. |
A small section of a fairly dusty sensor. I ran auto levels to make the dust more obvious. | |
| The normal way to check a camera for dust is to point it at the sky and take an exposure. I prefer to use a blank wall. Set the camera to aperture priority (Av), set the aperture to at least f/16 and take a picture of the wall. You may need to use manual focus (it doesn't matter if the picture is in focus) and about +1 exposure compensation. I like to move the camera as I take the shot - I was caught out once with a spot on the wall… Open the picture in your favourite editor and look at it at 100%. Scroll all over the picture and look for tell tale marks. If here are a few small ones then probably you don't need to worry. Unless you are shooting critical pictures with a huge depth of field it isn't worth worrying about a couple of specks. | ||
 | Delkin also sell a natty inspector to let you check your sensor. Pop the camera in cleaning mode and use the lighted magnifying glass to look at the sensor. If you can see the dust then you need to clean it. Otherwise don't bother. | |
Shake and blow
If your camera has a shaky sensor (and many recent Canons, Sonys, Samsungs, Pentaxes etc do) then engage the cleaning mode. This vibrates the sensor very quickly and attempts to shake the dust off. Repeat the check above. If the dust is still there then repeat up to about 5 times. If it's still there then chances are that it is stuck.
If you don't have a cleaning mode or it doesn't shift the dust then you might want to try using a blower. Note that the problem with blowers and self cleaning modes is that it simply moves the dust elsewhere. Sometimes this is into a dust trap and it will stay there but most often it will eventually reappear on the charged sensor. For this reason, some people will skip this step. When I blow the sensor then I only ever use a hand operated bulb blower. I like the Giottos Rocket blower partly because it has a valve to stop it sucking more dust in the back and partly because it looks cool on my desk. Of course you mustn't touch the sensor. You'll need to look in the manual to see how to put the camera in cleaning mode then use the blower carefully to blow dust off the sensor. Here are some of the crazy things you must not use to blow dust off a sensor. I'm sure people can come up with more.| Your breath | Seriously, you pay hundreds for a camera with a high precision sensor and then spit in it. You could probably even give your camera flu this way. The air coming out of your mouth isn't clean even if it is minty fresh. |
Canned air | Well, check the ingredients on a can of air. Does diflurourethane sound like the kind of stuff you want to coat a sensor in? Even if it was pure air the temperature drop as it comes out can be enough to make water vapour in it crystalise. Ever been in a hailstorm? Bet you wouldn't want your camera sensor hit with hailstones… Try spraying canned air onto a clean window. Then clean the window and go buy a rocket blower. |
Air from a compressor | I've actually seen camera techs do this. They use a very low powered compressor with a clean air source. I'm prepared to bet these cost more than a hand powered blower and unless you have exactly the right one it's risky. |
Blower brushes | Some manufacturers recommend these - personally I'd worry about hairs coming off the brush and jamming in the camera. People are also tempted to use these very close to the sensor because the blowing bit is a long way back from the tip. |
Dry contact cleaning
| There are a number of ways to do this. The basic principle is that you apply something to the sensor that will brush or lift the dust off. Remember that no manufacturer recommends touching the sensor with anything. One popular method is to use an artist's brush. You have to be very careful selecting the right brush. You need one with soft nylon filaments without size on them. Nylon will pick up static when you force air through it. Size is sticky stuff applied to bristles to make them more bristly - it would make a nice job of trashing your sensor. Once you have the correct brush the technique is to force air through it (using the same blower you use for blowing the sensor) to build up a charge then gently sweep the sensor with it. I've used this technique a number of times and it seems to work well. You do however need to be very careful selecting your brush. Another option is a purpose made brush from a company like Visible Dust. The hilariously named Arctic Butterfly has a custom made brush at the end of a motor driven handle. Spin the brush for 3 seconds to build up a charge and then sweep it across the sensor. The special filaments will suck the dust up. I have a Visible Dust system on test at the moment and a full review will follow. Visible Dust have some strong arguments on their website about why their brush is better than an artist's brush. |  |
Delkin Devices take a slightly different tack and provide a miniature vacuum cleaner with a special static tip to do much the same job.
A third product, new to the market, is the Dust Aid. If you want to clean dust of a monitor you can use a Post It note. The theory behind the DustAid is similar - an ultra low sticky substance on the end of a stick. Lower it onto the CCD and it will stick to the dust but not the sensor. The manufacturers have some impressive research to show that no glue will be left behind. (They use Fourier Transform Infrared Spectroscopy rather than just jabbing it on a piece of glass and taking a look.) Whichever method you choose, be careful not to wipe oil from the shutter mechanism onto the sensor. Canon 5Ds have particularly oily shutter mechanisms (it helps keep dust down!) and wiping the oil across the sensor is a quick way to learn about wet cleaning. Once you have used one of these methods check the sensor for dust again. If it's clean then stop right here - don't even think of wet cleaning.
Wet contact cleaning
All the warnings, caveats and disclaimers you've read so far apply double to this section. Don't even attempt this is you don't know what you are doing and be sure to read all the warnings. No camera manufacturer recommends this and there's no shame in putting your camera in for a service to get it cleaned properly. By somebody who is insured.
Sometimes you can get sticky stuff on your sensor. It could be oil from the shutter mechanism, particulates from condensation or even pollen. All of these are bad substances and unlikely to be removed by dry cleaning. You may choose to try wet cleaning. Wet cleaning is very easy. All you need is a perfectly clean, very soft wiper and some cleaning fluid that will dissolve the sticky gunk but not harm the sensor. As always, the devil is in the detail.A perfectly clean wiper
| The very soft bit is easy and if that's all you needed lots of things would do. The trick is getting something that is perfectly clean. If there's dirt or dust on the pad then the best case is you will leave it on the sensor. Worst case is you'll use the dirt particle to scratch the sensor and that would be bad. Also you need to be careful that it doesn't shed fragments of lint or cotton fibres. There are lots of methods on the web for making your own swabs. These range from fast food store knives to bits of credit card. They all require you to wrap a tool in a soft cloth. None of the cloths recommended stand up to any definition of “perfectly clean”. In fact the most commonly recommended is called “PecPad” and there is an explicit warning on the packet they come in not to use them for sensor cleaning. I would take no chances with this - I would buy something made for the job. There are plenty of sensor wipe tools available. They are all designed for the job and all are “perfectly clean”. None of them are cheap. It's very tempting to make your own but if you have followed the previous steps then you may find that you hardly ever need to wet clean your sensor. If you only do it once in a while it's worth buying the right tools for the job. |  |
Cleaning fluid
You need a fluid that will remove the gunk, leave the delicate sensor undamaged and evaporate without leaving a residue. Jeyes fluid ain't going to cut it here.
With one reservation this is a simple call. There are plenty of commercial fluids on the market that are designed for the job. Just like the pad you put it on, don't skimp. Get the real stuff even if it costs you extra. I know of no CCD that can be replaced for less than the cost of any cleaning kit on the market. The one reservation is that the fluid must be suitable for your sensor. Don't rely on your mates saying they have used “Brand X” for years - check with the manufacturer for your specific camera. Sensors have changed recently and there are reports that some fluids that are perfectly safe to use on some sensors are absolutely not safe for sensors with a dichroic or tin oxide coating. The Canon 5D and 400D and Sony Alpha 100 have this kind of coating. However, sensors are evolving all the time and it's possible that by the time you read this more cameras will have been added to the list. It's also possible there is some other coating that can be damaged by any of the fluids on the market now.One other thing to watch is that under current regulations most of the fluids on the market can't be taken on planes. The alcohol based cleaners are highly flammable and not the kind of thing that's allowed on planes. Stick to a non alcohol fluid if you want to fly with it.
Bottom line: only wet clean if you really have to. Buy the proper kit. Check that it really is the proper kit. Take care.
Can somebody do this for me?
Yep. Loads of people are queuing up for your business.
You can always contact your camera manufacturer and ask them to clean the sensor. Even if it is in warranty they will probably charge you around £50. Independent camera repairers will also do this for you if you find it all too daunting. In the London area Fixation offer a while you wait service. Take the camera in to them and they will clean it while you wait for £29.38 or £58.75 for a full frame sensor. Lehmans in Stoke will clean a camera in a couple of hours for £58.75 - but give them a call before you go. That will get very expensive over the life of the camera (I clean mine every 6 weeks or 2,000 exposures - in the summer that can mean every fortnight) but is useful for one offs. You might decide you will go as far as dry contact cleaning but leave it to the experts when you need wet contact cleaning.
technorati tags:photography, SLR, DSLR, dust, dust-remove, sensor, clean, cleaning-sensor
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