All the Olympus, Panasonic and Sony mirroless cameras share one thing: out of box, there are some micro dusts on their sensors:
To check the sensor dusts: set camera to manual focus mode and focus to infinite; set camera mode to aperture priority and set aperture to f/22 or the smallest; set zoom to 50mm equivalent or so. Open Notepad on your computer and maxmize it so you get a white screen. Put your camera possible to the white screen, take a shot while moving the camera slowly from the left to the right. Now open this image in XnView (or Photoshop), click Image, Map, Automatic Levels. Then you'll see something like above. The black dots you see are the dusts on the sensor, a dot on the left upper corner will appear at the right bottom on the sensor, vice versa.
To remove the dusts, you need these:
Don't use an Alcohol that contains either too much or too less water. Never touch the cotton tips to keep them from oil. Shake the swab as hard as you can to drain out extra alcohol before its touches the sensor. Move the swab to the edges of the sensor to minimize the trace.
This is how it looks now:
I also use this same method to clean lenses. Use a blower before and after above procedure. You only need to do such cleanup once, afterward it is almost impossible to get such factory dusts again. From now on, any dusts should be easily blow off.
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