Only the outer cameras produce 3D images.
Use a soft, clean cloth to clean the outer cameras.
The 3D images can become distorted and difficult to see if the outer cameras are used in direct sunlight or in the direct path of other strong light sources.
If the Nintendo 3DS system has been exposed to excessive physical shock or high temperatures, this may cause the outer cameras to display unclear 3D images. If you notice such a problem, recalibrate the outer cameras in System Settings.