The ray tracing for the right-side-up pin image coincident with the inverted pinshadow is complicated.
The black lines from the top of the pin show the
light rays spreading out from the pin head.
These rays are bent by the lens to create an image behind the retina, this is seen as an out-of-focus image on the retina located where all the black lines come together at the head of the blue pin.
The blue line shows one ray from the point of the
pin. This ray is one of many coming from the point which are brought
together to form an image of the point of the pin behind the
The fuzzy image of the pin is inverted.
The brain inverts the image again, so the silvery pin is seen as a right-side-up fuzzy image.
The red dot is a point of light such as the bulb of a mini maglight, or light coming through the pinhole in a filmcan.
Red rays of light come out from the light and
create a shadow of the pin.
The rays forming this shadow are bent by the optics of the eye and create a right-side-up image of the pin on the retina (shown in red).
The brain inverts this to create the impression of an inverted shadow of the pin.
The fundamental idea:
The cornea and lens of the eye bend light rays to make images.
They can bend light rays that spread out from a distant source to bring them into focus on the retina.
Light rays from nearby sources spread with such a large angle that they cannot be brought together to form an image on the retina.
Return to day 3
Scientific Explorations with Paul Doherty
22 May 2000