Digital cameras use a light sensitive sensor to record an exposure. In a digital single lens reflex, the mirror is in front of the sensor, providing it with a degree of protection from the elements and air as lenses are changed. With mirrorless systems like the Fuji X series, however, the sensor is exposed anytime a lens is removed. This allows dust or other stuff to invade and potentially cause spots on images. All modern digital cameras above the box-retailer price point have some system of “sensor cleaning,” which usually involves a mechanism to vibrate the sensor, knocking off casual dust. But my spots weren’t dust.
Instead, some internet investigation led me to believe that, based upon their size and shape, they were likely oil spatters. This is apparently not uncommon, though I hadn’t ever experienced it before. There are oils used in the manufacture of the camera, as well as in lenses, and sometimes some of it makes it way to freedom.
Determination of the problem made, further investigation led me to several companies who offer swabs for cleaning digital sensors. There are a variety, including dry swabs that you saturate yourself, as well as various parts one can buy to assemble one’s own cleaning tools. I opted for safety and ease of use by getting swabs that are pre-soaked.
Sensors come in all sizes, so it’s key to find out which swab size you need for the sensor you’re cleaning. The concept is that of a perfectly sized windshield wiper: the blade is the width of the sensor, so it will cover the entire sensor in one pass. This limits the possibility of scratches or introducing more crap onto the sensor.
You can check for sensor spots by shooting a clear sky or bright surface with the lowest ISO, the smallest aperture, and the lens fully out of focus. This will make the spots on the sensor stand out.
I don’t know the average experience for getting rid of sensor crud, but it took three swabs before I felt like I had made acceptable progress. The swabs aren’t exactly cheap, but it’s a small price to pay for clean images that don’t waste precious pixels.