https://www.youtube.com/watch?v=kYW9yDVw3bs
Keeping Your DSLR Sensor Clean
If you have a DSLR camera, you may have uploaded images at one time only to find that they have blotches. The blotches are usually constant in all your shots and they are usually because of a dirty sensor.
Although getting dust on the sensor will eventually occur, you can help to keep the chances of that happening low:
Do not change lenses in a risky area. Before leaving for your shoot, choose a lens and try to stick with it. If you have to change the lens, look for a confined area where there is no wind or dust to change the lens.
It is recommended that you switch off the camera when changing a lens. Some sensors have an electric charge that helps to attract dust particles towards it.
When changing the lens, ensure the camera is upside down. It is impossible for dust to settle on your camera if it cannot land on it.
Spend the least amount of time between lens changes. The longer your camera is left open, the higher the chances are that dust will affect it.
Always have a blower with you when changing the lens. Before installing the new lens, blow at it with the blower. That way, you can ensure that your sensor does not have any dust on it when you install the new lens.
If you have to clean the image sensor, do it with extreme caution. Some recommend that you get a professional to do the work for you. If you want to test your sensor, take photos on a white surface with a small aperture. It will help you identify if it has any specs of dirt on it.