How and when should I clean the lens?

• Clean the lens whenever you notice dirt or dust on the surface. Use a blower brush that is designed for camera equipment to remove dust from the lens. To remove dirt or smears, use a lens cloth or tissue. If necessary, moisten the cloth with lens cleaner and gently wipe the lens surface.
  
  Caution:
  Never rub the lens with abrasive materials. Use only lens cleaning fluids that are designed for cleaning optics.
  
  Warning:
  Before you clean any part of the projector, turn it off, unplug the power cord and let it cool down. Never open any cover on the projector, except the lamp and filter covers. Dangerous electrical voltages in the projector can injure you severely. Do not try to service this product yourself, except as specifically explained in the User's Guide.