When and How To Clean Your DSLR's Lens and Sensor

If you want to take consistently sharp photos, you need to make sure your camera's lens and sensor are both clean. If any smudges show up on the glass, or if any particles accumulate on the CMOS, you can expect fuzziness, spots, and other unwanted things to show up in your pictures. To do this, you need to do two things: protect your camera's sensitive parts, and clean your camera's sensitive parts when dirt still manages to get in. 

Protecting your lens from dust is actually extremely simple.
 
To start, purchase a UV or Skylight filter and keep it on the lens at all times. The clear filter will keep dust from getting onto the glass, and offer a measure of protection against bumps, scratches, and smudges, all while keeping your pictures as clear as if you didn't have anything over the lens. Filters can be as cheap as $10, and can offer the added benefit of reducing haze on sunny days. 
 
A filter can't protect against everything, and you should still be prepared to clean your lens if necessary. Digital Photography School has a handy guide detailing exactly how to clean your lenses (and how to clean your filters, since they'll get dusty in lieu of the lenses themselves if you use them). Cleaning cloths or lens tissues bought specifically from camera stores (or the photography sections of electronics stores) are designed to clean lenses without scratching the glass, and when used in conjunction with an alcohol-based cleaning fluid you can even get off fingerprints and other unsightly marks. Other tools, like small blowers and fine lens brushes, can help remove dust from your lens. 

Camera sensors are much more delicate than lenses, and both protecting and cleaning them is appropriately trickier. Digital SLRs form a very good seal between the camera body and the lens, producing a very good level of protection against exposing the fragile sensor to dust and other pollutants. However, whenever you switch lenses, you break that seal and leave the sensor wide open to danger. To keep your sensor protected, you need to minimize the amount of time the camera's internal components are uncovered. Fortunately, the SLR Photography Guide Blog has a very good technique for changing lenses quickly and easily.   
     
Hold the camera body in your left hand with your index finger on the lens release button. Hold the lens you want to switch to in your right hand with your thumb, index finger, and middle finger, making sure your thumb is aligned with the lens alignment dot. Grip the end of the lens currently on your camera between your right palm and the last two fingers on your right hand. Press the lens release switch, twist the lens currently on the camera and remove it from the mount, and put the new lens in its place. With practice, you'll be able to change a lens in under three seconds. Make sure you practice over soft carpet first, though; the last thing you want to do is fumble and drop your lens on concrete while trying to protect your sensor. 
 
You still might have to clean your SLR's sensor from time to time. This is a tricky process that shouldn't be done on a whim. Only if you see significant dark spots in your photos not explained by the shot (indicating dust on the sensor) should you clean your sensor. The web site Cleaning Digital Cameras offers a lengthy (and detailed) explanation of how to clean your sensor, going over multiple techniques and pointing out the dangers and pitfalls. Sensor swabs seem to be the most common and reliable way to clean your sensor, but you can also purchase entire cleaning kits or use special tools like vacuums, brushes, and blowers.  
 
If all else fails (or if you don't want to poke at the sensor yourself), you can get your camera professionally cleaned at a camera repair shop. This is easily the most expensive way to clean the camera, though, with services easily costing nearly $200. It also requires that you hand off your camera to a repair shop, meaning instead of shooting again in a few minutes, you'll have to wait a few days. Consider professional cleaning only as a last resort. 
 
Images via Flickr user m-louis, avlxyz, waikin