How to Clean Your Camera Sensor.
Compact and mobile phone cameras have one big advantage over system cameras: the sensor inside the camera is never exposed to the elements. The reason that this is an advantage is that sensors in system cameras invariably pick up spots of dust and other stuff such as pollen. Sensors have an electromagnetic charge that attracts dust, in much the same way that old-fashioned CRT TV screens do.
This is a 100% view of an image shot with an early DSLR. The sensor was a real dust magnet and needed regular cleaning.
Fortunately, camera manufacturers have spotted this flaw and have done their best to mitigate the effects of dust. Most modern camera systems have cleaning mechanisms that rapidly vibrate the sensor for a few seconds (or more correctly, it's the low pass filter in front of the sensor that's vibrated). This literally shakes the dust off and is generally very effective.
However, older cameras without cleaning mechanisms invariably need cleaning every so often. Even newer cameras with a cleaning mechanism can't cope with wet dust or moisture spots. These sticks to the sensor and can't be shaken off. So, what do you do?
The easiest way to deal with dust is to have someone else sort out the problem. Camera stores and service departments will happily clean your camera's sensor for you. However, they won't do this for free. Add up the cost of each trip to have your camera's sensor cleaned and you'll soon realise how much you could have saved by doing it yourself. The one problem with cleaning a sensor is that being careless can prove expensive. It's possible to scratch a sensor and believe me you really don't want to.
Oddly enough however your camera's sensor may be covered in dust and you may not even have noticed. The visibility of dust is affected by the aperture you use. It's all to do with depth of field, the smaller the aperture the greater the depth of field and the more visible dust will be. It's one of two good reasons not to use f/22 every time you take a shot (the other reason is diffraction, but that's an issue for another day).
Dust is also generally more visible in areas of light, even tone. Skies are a good place to spot dust. Dark, textured surfaces are less likely to show up dust. If you regularly shoot dark, textured surfaces with large apertures the problems of dust may be insignificant.
There are three basic ways to clean a camera sensor: blowing, dry or wet cleaning. Blowing simply involves passing a current of air across the sensor to shift the dust. This is achieved either by using a blower, such as a Rocket Blower, or compressed air. What it doesn't mean is blowing onto the sensor yourself. That can cause all sorts of problems that can make the situation worse.
Dry cleaning involves either using a charged brush that's gently wiped across the sensor (such as an Artic Butterfly) or by pressing a special sticky pad onto the sensor (Dust-Aid) . The brush is charged by rapidly spinning it for a few seconds. The charge is strong enough to lift the dust off the sensor. However, blowing and dry cleaning can only cope with dry dust, neither can clean away moisture spots for example.
For stickier dust you need to wet clean your sensor. This is achieved through the use of a specially-designed swab that's been impregnated with a cleaning fluid (typically this is an alcohol-based solution, though detergent types are available too). The swab is dragged gently across the sensor once and then thrown away (you should never use a swab more than once).
It's a little bit scary the first time you clean a sensor. But it's worth it. There are far better things to do with your time than cloning out dust spots from your images after shooting.