All of our gadgets are susceptible to dirt simply because dirt is everywhere. Your DSLR image sensor, just like any other equipment or equipment parts, can catch dirt and other substances that are not supposed to be there. It's important to always be aware of the possibility of contaminating your camera's sensor to avoid imperfections in your images, as well as possible damage to the camera. Here are some of the ways you can protect your DSLR image sensor from dirt:
1. Keep your lenses clean
This is obvioously a very basic principle, but it's something we all need to be reminded of at times. Be sure to clean your camera lenses before attaching them to your camera. Dust or dirt on the inner lens surfaces can not only show up in your photos, but can also transfer to the sensor surface, becoming permanent flaws in your images. Always check your lenses before attaching them and use a lens brush and/or blower to remove the smallest specs of dirt. If you choose to use a wipe or cloth, be sure to use material specifically designed for camera lenses to avoid doing permanent damage.
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2. Turn the camera off when swapping lenses
Your camera should be turned off when you replace the lens, as static electricity can attract dust like a magnet when the camera is on. It's also a good idea to keep the front of the camera pointed down while it's open, since gravity is going to pull any floating particles into the opening otherwise. Naturally, if you set the camera down, you should place the body cap on it to prevent trapping dust or worse, damage from larger foreign objects.
3. Be aware of your current environment
Don't remove or replace your lens in risky settings and environments. For example, if you're shooting on the beach and need to replace your lens, try to find a closed room or vehicle and swap your lenses there. Salt, water and sand can have devastating effects on your camera's sensor and other mechanisms. If there's a need to swap lenses outdoors, prepare everything first and make the swap as quickly as possible. An old-fashioned film changing bag can be a very good investment for shooting in harsh environments or inclement weather.
4. Take some test shots
Before you head out or set up the studio for a shoot, take some test shots to check the condition of your sensor. Just focus with a very clean lens on a very clean, bright white surface and shoot a few frames, then download them to your conputer to inspect them at high magnification. Dust on your sensor will show up most often as dark blotches, often round and sometimes with an indistinct shape. If you find your sensor is dusty, save yourself some post processing time and clean it with a good blower, then check it again. If dust spots persist, you'll need to carefully clean the sensor or, better yet:
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5. Let a professional do the job
There are ways to clean your image sensor yourself, but keep in mind that there's always a risk of permanently scratching its protective cover. If you're at all unsure of yourself, professional cleaning is highly advisable. A simple sensor cleaning is often a walk-in service at your local camera shop and rarely costs much. In any case, it's much less expensive than replacing the sensor or its cover, especially if the camera has to be shipped to the manufacturer. We recommend never using anything but a blast of air from a bulb-type blower to try to clean the sensor on your own.
Note: Most modern DSLRs use an electonic sensor cleaning feature that activates when you turn the camera off. If your sensor is dusty, you may find that facing the camera downward with the body cap on and turning it on and off can dislodge dust.