Casio XJ-450 - Manual (Page 17)

General Guide
17
6
Lens : Projects the image from the projector.
7
Sensors : Measures the distance between the projector and screen.
Warning Never look into the lens while the projector is turned on.
Caution
z Finger smudges or dirt on the sensors can cause keystone
correction problems. Should the sensors ever become soiled, wipe
them clean using a commercially available lens cloth or optical lens
paper, like those for eyeglasses or camera lenses.