The optical system in the photograph includes the following: bright point source with condenser lens, ground glass screen, wire mesh object, first iris, 8 cm focal length lens, second iris, and distant screen, as seen in the photograph at the right above.

Set the two irises to about one-third of their maximum opening to obtain a distortion free image (photograph at left below). Opening the second iris (preceding the lens) causes pincushion distortion (photograph at center below), while opening the first iris (following the lens) produces barrel distortion (photograph at right below).

The optical system in the photograph includes the following: bright point source with condenser lens, 5cm focal length plano-convex lens with flat side toward light source, copper wire screen, and 10 cm diameter 23 cm focal length convex lens. The image of the wire mesh is cast on a screen at about 10 feet from the optical cart.

To produce barrel distortion, position the wire mesh close to the first lens and position the large lens about 23 cm from the mesh to focus the image of the mesh on the screen, as shown in the photograph at the left below. The resulting barrel distortion is seen in the left center photograph.

To produce pincushion distortion, position the wire mesh about 15 cm from the first lens and position the large lens about 23 cm from the mesh to focus the image of the mesh on the screen, as shown in the right center photograph below. The resulting pincushion distortion is seen in the photograph at the right.

This demonstration also shows "curvature of field," because the focal position of the 23 cm lens is different to focus the center of the mesh than to focus the periphery.

View from within a few feet to observe chromatic aberration.

This demonstration provides a more diverse technique for producing barrel and picushion distortion. The optical system in the photograph includes the following: bright point source with condenser lens, 5cm focal length plano-convex lens with flat side toward light source, copper wire screen, and 10 cm diameter (approximately) 15 cm focal length focusing concavo-convex meniscus lens. The image of the wire mesh is cast on a screen about 10 feet from the optical cart. The photographs below show the detailed setups used to achieve either barrel or pincushion distortion (top row) along with the distorted image produced using each setup (bottom row).

In the pairs of photographs at the left and left center, the screen is positioned about 15 cm from the first lens, and the meniscus lens is positioned to focus the image of the wire mesh on the screen. To obtain barrel distortion the lens must be about 12 cm from the wire mesh and the convex side of the lens must be facing the screen (set at left). To obtain pincushion distortion the lens must be about 18 cm from the wire mesh and the convex side of the lens must be facing the light source (set at left center).

In the pairs of photographs at the right center and right, the screen is positioned close to the first lens, and the meniscus lens is again positioned to focus the image of the wire mesh on the screen. To obtain barrel distortion the lens must be about 18 cm from the wire mesh and the convex side of the lens must be facing the light source (set at right center). To obtain pincushion distortion the lens must be about 12 cm from the wire mesh and the convex side of the lens must be facing the screen (set at right).

Viewed from about 30 cm in front of a large diameter 20 cm focal length convex lens, the back edge of a matchbox about 10 cm behind the lens appears longer than the front edge.

For large groups, a TV camera is positioned about 30 cm in front of the lens, as in the above photograph.

Several types of Fresnel lenses are included: (1) a sheet of 20 identical divergent (concave) Fresnel lenses (seen in the photograph at the right above), (2) a 12" diameter divergent (concave) flexible Fresnel lens, called a "Lensor" (seen in the photograph in the center above), and (3) convergent (convex) Fresnel lenses of 5.9, 12.5, 14.5, 15.2, 22.5, and 30.5 cm focal lengths, among others.

The convex Fresnel lenses were obtained from a facility which manufactures optically programmed traffic signals (See Demonstration L6-54: OPTICALLY PROGRAMMED TRAFFIC SIGNAL - MODEL.)

The overhead projector platform is covered by two color filters, arranged so that the left section is green and the right section is red, and the entire projector except the exit lens is covered by a box. When the lens is aimed at the class, the red and the green areas are focused such that any student sees either red or green, as in the photograph at the right above.

Optically programmed traffic signals make use of Fresnel lenses in a similar type of optical system to allow the light to be seen only in certain lanes of traffic. Optically programmed traffic signals can be identified because they should be rigidly attached to some support and they are rather soft colors (not bright like direct lights).

A frame of a wide-screen movie is projected through a normal lens (far right above) and an anamorphic lens (center) which magnifies the horizontal axis more than the vertical axis. The anamorphic lens is constructed using two cylindrical lenses with different focal lengths. In this demonstration the beam is split after passing through the film. One half of the beam is focused onto the screen by the spherical lens; the other half is focused by the combination of a 20cm cylindrical lens focusing horizontally and a 30cm focal length cylindrical lens focusing verticlally.

Projectionists apparently call this a " 'scope lens." Such a lens is available (see picture at left above) for individual viewing.

This model uses the electrically operated blackboards in the physics lecture halls to model a focal plane shutter.

Move the rear board to its lowest visible position and move the front board out of sight (down). Now start the rear board moving up; this is the shutter opening. Then start the front board up; this is the shutter closing. If you allow the rear board to get to the top before you start the front one, this illustrates how the shutter works at slow shutter speeds. If you start the front board up before the rear one gets to the top you simulate faster shutter speeds. Stop the boards when the entire area is covered. Move them back down together to show how winding works to reset the shutter.

The laser beam is aligned with the photocell in the black aluminum cylinder, which is connected to a timer with large display. The camera is mounted on an optical post with the standard camera thread on one end, and positioned so that the laser beam will reach the photocell when the shutter is open. Reset the counter and cock the camera, and timer will measure the shutter opening time when the "picture is taken." Alignment is simpler if the lens is removed from single lens reflex cameras.

(1) Depth of field: Open the lens aperture with the Fresnel spotlight off, set the camera to full zoom (100), and place the camera at the closest distance at which it is possible to focus on the nearest can. Focus on the middle can, and observe the focusing of the extreme cans (photograph at right). Then turn on the spotlight so that it illuminates all of the cans and close the f-stop so that the lighting level is the same as before. Observe that the depth of field increases, because the increase in light level allows use of a smaller aperture (photograph at left).

Field of view: Vary the zoom and observe the change in the size of the field of view.

Illustrate how the various optical features of the camera work as well as other features of the minicam as desired. Show the picture on the video rear projection screen above the blackboards. Controls for the camera are shown in detail in the photographs below.

The photograph at the center shows the main focus and shutter controls. At the right are the manual controls for focus and zoom, along with the macrozoom control lever (near bottom of picture). The photograph at the left shows the ON/OFF button for videorecording, the built-in microphone (top), and the rocker switch for telephoto and wide angle adjustment (center of picture).

A lens at the left (out of picture) produces parallel light, as from a star. The second lens (at left in photograph) is the telescope objective, and the lens at the right is the eyepiece. The parallel beam of rays entering the objective lens is wider than that emerging from the eyepiece, indicating the ability of the telescope to "gather" light. When the position of the "star" is changed (photograph at right) by moving the source up (rays entering the telescope at a downward angle), the image is moved down and the angle at which it is viewed (inverted) is magnified relative to the incoming light, indicating the ability of the telescope to increase the angular separation of the stars it is viewing.

Choice of slit baffle and distance of baffle from source determine the number of rays and their spacing.