### Disposable Camera Dissection

By "dissecting" a disposable camera, students can explore the mechanics of a camera. They can observe the shutter mechanism, a combination of springs and gears. They can remove the main plastic lens and determine how the camera forms an image on the film. Students can determine the focal length of the lens. Students can study the viewfinder, using it as an example of a double lens system. Students can determine how a magnifying glass can be used to create a virtual image by observing the lens that magnifies the number of pictures remaining on the film.

Objectives:

1. To create real and virtual images using disposable camera optics systems.
2. To determine the focal length of a lens.
3. To relate the shutter mechanism to conservation of energy principles.

Procedure:

Safety goggles must be worn due to danger from flying parts. Do not let students handle flash cameras. Disable the flash mechanism before allowing students to handle the camera (See below).

1. Instruct students to take apart the camera. The parts of the camera are easily snapped apart.
2. Students should carefully observe the combination of gears and springs comprising the shutter mechanism. Urge them to determine how it operates. In the cameras that my students dissected, there was black knob inside the camera that students turned until it could go no farther. Cameras varied by desing, by my students found they could open the shutter by next pushing on a switches or springs that they found in the camera. Students were amazed at the shutter speed.
3. Instruct students to remove the plastic lens in the main body of the camera. My students were amazed at how small it was. It can be easily mounted on a piece of cardboard or manila folder. Instruct students to experiment with it to create images and to determine its focal length.
4. Instruct students to remove the viewfinder system. My students initially thought that this was simply a concave lens. Upon further study they determined that it was used in conjunction with a convex lens. Have students look through the double lens system and describe the image produced. Have them compare that to one produced by only a concave lens.

Suggestions for Further Study:

1. Dissect a sheep's eye and compare its parts to the camera's shutter mechanism, optical system, and film. The sheep's eye dissection and comparison to the camera created lots of discussion in my classes.
2. Have students construct water lens and compare them to the camera. These can be made from a 1/2 inch straw segment that one end has been closed off with tape. Fill the straw with water until the meniscus "bubbles" over the rim, forming a convex shape. Have students view a square drawn on paper by setting the convex water lens on top of it. Let the water leaks out of the lens so that it becomes concave. Have students describe the differences in the image produced (My students informed me that a water lens was made out of a blade of grass in the movie A Bug's Life).
3. Have students construct a pinhole camera. They can glue a piece of paper between two small Styrofoam cups which are then glued together. A one inch diameter hole is cut in the bottom of one cup. The cups are wrapped with aluminum foil. A pinhole is punched through the aluminum foil bottom of the cup of the other cup. Have students view an incandescent light bulb using their pinhole camera.

Disabling the Flash Mechanism:

I learned the hard way how to do this. I would never let a student touch a flash camera until I had removed the flash assembly due to danger from electrical shock. Students were impressed with a demonstration of how the flash assembly worked.

This procedure worked best for me:

1. Open the camera and remove the battery.
2. Carefully remove the circuit board containing the flash circuit from the camera. I carefully pulled up an edge to find the large black electrolytic capacitor. Do not touch the capacitor's leads and do not touch the two soldered connections for the capacitor on the opposite side of the board.
3. Hold a screwdriver by its insulated handle. Use it to short circuit the capacitor leads. This causes a large and spectacular discharge.
4. Repeat the discharge process because the capacitor does not fully discharge with one try.
5. The flash circuit is now safe to be removed. As long as the battery is not returned to the circuit and the capacitor has been successfully discharged, it is not an electrical shock hazard.
References:

The camera dissection is based upon "Camera and Telescope Free-for-All!" by Gene Byrd and Mark Graham, The Physics Teacher, vol. 37, Dec. 1999, pages 547 -550.

Directions for the water lenses and pinhole camera were found in String & Sticky Tape Experiments by R. D. Edge, a publication of the American Association of Physics Teachers.