PURPOSE: Model image inversion on the retina.

DESCRIPTION: A TV camera models the eye to demonstrate that the image on the retina is inverted, and how this arises. A pinhole illuminated by a small light bulb is placed inside the near point of the eye. The head of a pin is inserted into the light path between the eye and the pinhole from below, but appears to be entering from above.

The image of a distant object is inverted on the retina or TV videcon. The head of the pin, however, casts a shadow because it is inside the near point of the TV (or eye) lens. The shadow is on the lower part of the retina, which is the upper part of the image because of the inversion.

SUGGESTIONS: Use the 0.6mm aperture, set the TV camera focus to infinity, and open the aperture of the camera to its largest value. See Question of the Week #237 for information on using this demonstration to enhance class involvement.

REFERENCES: (PIRA 6J10.40) See Demonstration O1-03: IMAGE REVERSAL ON RETINA - INDIVIDUAL VIEWING for an individual demonstration of this effect.

EQUIPMENT: TV camera with standard lens, mounted pin, pinhole, and 7W light source, mounted on optical rail on mobile TV monitor cart.

SETUP TIME: 5 min.