When black splotches appear in all of your photographs in the exact same spot, chances are you have dust or dirt on your camera’s image sensor. Dust usually lands on the sensor when the photographer is changing lenses. This will more than likely happen to all photographers, but here are some tips to decrease your chances:
-Do not change your lens outside when there is lots of wind, water or dust. In these environments, pick a lens and stick with it.
-Always turn your camera off before you switch lenses.
-Hold your camera toward you or even upside down when changing lenses. It is unlikely that dust will fall into your camera if it’s upside down.
-When changing lenses, have your replacement close and ready to attach as soon as you remove the first lens. This way your camera is only open and vulnerable for a few seconds.
-Check your lenses for dust before you attach them to your camera.
-If you decide to clean your image sensor, do it with care. It is advised to seek help from a professional though.
Rowse, Darren. “How to Avoid a Dirty DSLR Image Sensor – Digital Photography School.” Digital Photography School RSS. Digital Photograph School, Web. 1 May 2014. <http://digital-photography-school.com/how-to-avoid-a-dirty-dslr-image-sensor/>.