Sensor cleaning

How to use 'dry' cleaning for dust, 'wet' cleaning for stubborn spots and smears.

The sensors in digital SLRs do sometimes need cleaning. The usual problem is dust spots, and although many cameras now have dust removal systems which briefly vibrate the sensor (or a filter in front) to dislodge any dust, these are not always effective. Some dust is just too 'sticky'.

Cameras without in-built sensor-cleaning systems are more prone to dust spots, and the image above shows what they look like (dark, diffuse spots).

Sometimes, the sensor can also pick up smears. These aren't as obvious in their effects as dust spots, but can cause subtle streaking effects or reduced resolution and contrast. Smears may be caused by lubricant spraying from the mirror mechanism (a problem on some Canon cameras, illustrated above), or by previous cleaning attempts. If you're not careful when using a sensor swab, you can drag lubricants from around the sensor mount and on to the sensor surface itself.

Depending on the problem (dust or smears), there are two approaches you can take to sensor cleaning: 'dry' cleaning and 'wet' cleaning.

'Dry' cleaning

This is sometimes done with a blower, but often these simply stir up dust inside the camera body and make the problem worse. Usually, a brush is the best solution, but it has to be a special sort. An ordinary brush, like those sold as camera cleaning accessories, is no good because the fibres collect dust and grease over time. They'll just leave the sensor a whole lot dirtier than it was before.

Instead, you need a specialised sensor brush, like Visible Dust's Arctic Butterfly. This uses electrical charge to pick up dust on the sensor surface, and this charge is generated by spinning the brush (it has a battery and motor) for a period of several seconds before passing it gently across the sensor surface. It may take a few attempts to remove any dust, but the risk of contamination or abrasion damage is much lower.

'Wet' cleaning

This may not be enough, and some people find that a dry clean with a specially-designed sensor 'swab' (below) may shift particles that a brush won't. It's more usual, though, to use swabs as part of a 'wet' clean, in conjunction with a specially-formulated sensor cleaning solvent.

Swabs are shaped like paddles in sizes designed to match APS-C or full-frame sensors (make sure you get the right size). They are sold in individually sealed packages and can only be used one. The fluid you use is crucial too. Ordinary lens cleaning fluid is no good; it has to be proper sensor cleaning fluid.

The trick with sensor cleaning is to stop when you've done enough, but it can be pretty hard to work out when that is with the naked eye. It's usually worth investing in a sensor loupe (below), which combines a magnifying lens with small lamps which illuminated the sensor surface.

If you send your camera away to be professionally cleaned, the technicians will be using the same materials and techniques we're describing here. Hopefully, they'll have the benefit of experience and will do a better job than you could, though you can't always rely on that.

One final word of warning. If you scratch your sensor when cleaning it, it's your responsibility and you will have to pay for a repair, whether or not the camera is still within its warranty period.

Dust removal systems only work sometimes

Pretty well all D-SLRs and hybrid cameras now have some kind of dust-removal system that shakes the sensor (or a filter in front of the sensor) to dislodge dust particles. But not all dust particles dislodge so easily, and not all sensor debris is dust, so there's a good chance you'll have to clean the sensor yourself at some point anyway.


'Dust' can be light, 'dry' particles that shake free easily, but pollen grains are sticky, tiny airborne fibres may have oily content and tiny atomised specks of sea spray will contain salt, and these aren't going to just shake loose.

So look out for cameras with dust-removal systems by all means, but whatever the makers might claim, they will only deal with certain sorts of dust. It's all down to luck and the kinds of environments you shoot in.

Low pass filter | Your sensor is protected!

Low pass filters are placed directly in front of sensors to reduce the incidence of interference or moire effects. They also act as a useful protection for the sensor surface, and on some cameras the low pass filter can be vibrated to dislodge dust particles.

In fact when you look at a sensor, it's the low pass filter you see, not the sensor surface itself. It's the low pass filter which collects the dust and smears in a digital SLR, and it's the low pass filter you're cleaning when you remove it.

This is a photograph of the Panasonic GF1. What you see through the lens throat is the surface of the low pass filter, and the sensor surface itself is completely covered by it. This camera has a dust removal system which vibrates this low pass filter to remove any dust. The filter prevents the dust reaching the sensor itself. The GF1 isn't a digital SLR, but the principle of the low pass filter is the same on D-SLRs.

This means, incidentally, that sensor cleaning is not necessarily the terrifyingly hazardous process that the camera manual may suggest. You're not cleaning the super-delicate silicon surface of a chip containing millions of microscopic photosites, but an altogether more robust optical filter in front of it. It's still possible to scratch the surface of a low pass filter, of course, especially since they're so hard to get to, but if it's approached carefully sensor cleaning should be quite safe.

Low pass filters are needed because sensors use rectangular arrays of photosites and if you're photographing a subject whose detail includes a fine rectangular mesh of a similar pitch (iron railings in the distance, maybe, or woven fabrics), there's a good chance of interference effects which appear as tiny colour fringes and artefects in the image.

Low pass filters are necessary, then, but they have a side-effect. They work by slightly blurring very fine detail, and this is one of the reasons why digital images always need some kind of sharpening, which usually takes place in the camera and sometimes again when they're being edited on a computer.

This is illustrated by this photograph taken with a Nikon D50. The strength of the low pass filter in the D50 is unusually low, and the result was that this camera's rendition of fine detail exceeded any other 6 megapixel cameras of the time. The bad news was that some subjects would produce interference/moire effects, visible here as diagonal stripes in the railings on the side of the pier.