You can study mechanics, optics and even electronics by dissecting a one-use camera.
Material
Etc
To obtain the cameras emphasize that you are a teacher and that you would like to help the store to recycle the cameras.
Destruction
If the camera has a paper covering, remove the paper. Open the box at one end and slide the camera out. (One end is probably open already since the camera store removed the film.)
It is best to start with a camera which doesn’t have a built-in flash. If the camera has a flash, you should locate and remove the AA battery to reduce the chance of getting an electric shock. Remove the battery as soon as you get the camera to allow plenty of time (several hours, or even better, days) for the internal capacitor to discharge.(More on flash unit dissection in another Exploration. Go to Camera Electronics)
Use the screwdriver blade to pry the back off the camera. You can pop the backs off cameras without breaking any plastic. Follow the seam around the camera prying it gently apart while looking for snaps and other latches. It is often easiest to pry off the back starting with the right side as you view the upright camera from the back(drawing).
To do and Notice/ What’s going on
Can you figure out how the film advance mechanism works?
Usually, you turn a wheel on the back right top of the camera with your thumb. The wheel is connected to the film take-up spool. The film is attached to the spool. Turning the spool pulls the film through the camera.
Can you make the shutter work?
Press the shutter release button. Did you hear a click of the shutter opening and closing? Probably not, because the shutter did not work.
To make the shutter work, you must cock the spring which drives the shutter’s motion. In the center top of the inside of the back of the camera is a sprocketed wheel. Turning this wheel cocks the shutter. The sprockets of this wheel go through holes in the film. When you advance the film, the film turns this wheel.
Turn the sprocketed wheel by hand pushing the sprockets to the right until you hear a click. Now, when you press the shutter release button on top of the camera, the shutter will open and close with a click. (In some cameras you have to turn the sprocketed wheel until you hear a second click.)
Cock the shutter again. This time, look through the shutter at a roomlight when you press the shutter release and notice the flash of light as room light passes through the open shutter.
(If your camera has a flash go to the
flash
section now.)
(Optional, Try to measure the time the shutter is open. Shine a light
through the shutter onto a solar cell attached to an
oscilloscope.)
Pry the top off the camera.
Notice the plastic gears and levers.
Notice what happens when you rotate the wheel which cocks the
shutter.
Notice how the shutter release works.
There is a logic device in the camera which makes it so you cannot double expose film and you cannot advance film without taking a photo.
The logic device is an odd shaped piece of metal or plastic! How does it work?
How is the film stopped after it is advanced exactly one frame?
What moves the shutter?
(usually a spring, some cameras use 2 springs.) What kind of springs are they? Coil springs or other?
How does the shutter work, i.e. how is it made to
open then close?
How is the shutter timed so that it opens for the correct length of
time?
(The acceleration of a shutter whose mass is known by a spring whose force is known can be used to determine the time for which the shutter is open.)
From the front, take apart the lens assembly.
Where is the stop, the hole which limits the amount of light
which enters through the lens?
(Some cameras have two lenses and the stop is between them.)
What is the focal length of the lens (or of each of the lenses)?
(The focal length of the lens or lens combination ought to be close to the distance from the lens to the film.)To measure the focal length, make an image of a distant light, the focal length is approximately the distance between the center of the lens and the image.(Distant means at least 10 focal lengths away so the ceiling lights usually work well.)
What kind of lens(es) is it (are they)? (concave,
convex, meniscus etc.)
Notice that you can use the lens or lenses as magnifiers.
Complete the disassembly of the camera. Then reassemble it to see if
you really understand how it works. (Or you can save the gears,
levers and springs for other projects.)
Hot melt glue the parts to a 5 by7 card labeling each
part.
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Scientific Explorations with Paul Doherty |
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22 June 99 |