Step1
Choose a clean and dust-free area of near a window in your room where you can get access to the direct sunlight. Spread out a clean sheet, and put all your stuff on it.
Step2
Remove your lens from the body of the camera, and cap the lens. Now, inspect the camera under direct sunlight. Sunlight is the best source of light to inspect your camera, as you will be able to see even the smallest particle. Look for any scratches, dirt, grease and other signs of wear.
Step3
Identify the parts you'll need to clean. Most digital SLR cameras have three parts to clean: the focusing screen, the mirror and the sensor.
Step4
Start by cleaning the mirror. After inspecting it under the sunlight, spray some lens cleaning fluid on cotton swab. Now, gentle "mop" the mirror surface in one direction. Then, with the help of the brush, repeatedly sweep the surface until the stains of the lens fluid are removed. It will take you many more gentle sweeping motions of the brush before you see a clear, sparkling surface.
Step5
Next, clean the focusing screen. DO NOT use any cloth, q-tip or lens fluid. Even though the dust particles on the focusing screen do not effect the quality of the images but it can be very annoying to look through a dirty view finder. The only gadgets that I recommend for this purpose is a clean brush (that has been blown thoroughly with an electric blower) and the air blower. Use brush only if you see sharp dust particles in the view finder. Do not apply even the slightest degree of pressure on the brush while you are sweeping the focusing screen.
Step6
Last and most vital is cleaning the camera sensor. There is no easy access to it. You must read the user manual of your camera to learn how to expose the sensor. Even if you lift the mirror, you still wont be able to see the sensor because it lies behind another flap, which you cannot and should not attempt to lift. After you have exposed the sensor, clean it only if it is extremely necessary. Otherwise, just leave it alone. Once exposed, inspect it under the direct sunlight as quickly as possible. The direct sunlight may damage the sensor if exposed for too long. If you see dust particles sitting on the surface, an air blower would be more than sufficient to clean it. If, however, the surface of the sensor looks dull or there is grease sticking to it, then you would need to carefully and gently clean it exactly the same way that you cleaned the mirror (only 100 times more carefully and gently). While using the brush, keep sweeping until you see a sparkling sensor. After that, switch on your electric air blower. First, make sure it is clean. Put a clean piece of cloth or a brand new air filter at the inlet of the blower so that the air that is gushed through its tube is free of dust particles. Blow right in to the camera sensor. Before closing the sensor, inspect it once more under sunlight. If everything looks OK, turn off the camera. This will allow the sensor to hide back in its position.
Step7
After you have cleaned the sensor, blow air inside the camera. This will remove any dust particles and fibers from the mirror and the focusing screen that may have collected while you were cleaning the sensor. Do not forget to inspect the mirror and the inner walls of the camera under sunlight before mounting the lens back.
How to Clean Your Nikon Digital SLR Camera from Inside.
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