PPT
Pinhole Camera
Developer Notes
 Exercises need improvement.
 A pin-hole camera (camera obscura) was first ? It might be good to have a little history here.
Maybe even on the first cameras.
Version
01
02
Date
2004/07/07
2005/01/05
Who
sc
dk
03
2005/04/13
dk
Revisions
Initial version
Removed these goals:
1. Students should understand that light is a type of
wave (electromagnetic wave).
2. Students should understand that light waves require
no medium to be transferred through.
3. Students should understand that light has energy (it
does work)
Updated per Arny’s notes
Goals
1. Students should understand that light is a wave and emitted in all directions.
2. Students should understand that light rays travels in straight lines.
3. Students should learn to draw light rays.
Concepts & Skills Introduced
Area
Physics
Physics
Concept
Light waves
Images
Standards Addressed
Time Required
Warm-up Question
Presentation
The main goals here are to reinforce that light radiates (is a field) and travels in straight lines (for
everything we can see). Students should also learn to draw light rays. Students may recall the ray
diagrams from the inverse-squared activity.

Tin cans work nicely for this activity. They aren’t flammable, they’re pretty tough for
storage, they don’t rust, they’re cheap, they’re hand size, and they’re opaque. Use cans about
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Pinhole Camera
100 mm long. Cut one end out. Make two round holes near the center of the other end. Make
one hole about 3 mm diameter, and the other about 1.5 mm diameter. Drilling the holes
works well. The rounder, the better. Make another can with both ends cut out - you may need
to eliminate internal reflections by blackening the inside with either flat black spray paint or
black construction paper.
White plastic grocery bags work pretty well for image screens. They’re translucent and can
be stretched pretty flat. Also cheap. Cut them to size and use rubber bands to hold them on
the open end of the cans. Wax paper can also be used. The screen should be as smooth and
flat as possible.
If you don’t have good images to view, candles work pretty well as a light source because
light comes from every part of the flame, and the flame is not symmetrical. A frosted
chandelier bulb might work well also, but I haven’t tried it. Candles are flames, which is a bit
dangerous, but they don’t require wiring and electricity. Flashlights don’t have asymmetrical
shapes.
A viewing tube helps a lot. Roll a piece of opaque paper into a tube (black construction paper
works well) and rubber band it around the can. Images will appear much brighter.
Start by looking at some object in your hand (an apple?). This is a repeat from the stations.
Everyone can see the object because light is reflecting from it in all directions. Draw a ray
diagram of the object, with rays emanating from one point in all directions (to all students).
In the activity, it would be good to hand out the huge-hole cameras first, so students don’t get
ahead of themselves. Go to the pin-hole cameras after analyzing the huge-hole cameras. Students
should look around using the huge-hole cameras. They can look at the lights in the room, the
windows, anything that is fairly bright, preferably something with detail in it. Buildings across
the street work well. They should note that the screen is lit up all the way across. The image of
the object is impossible to make out. Make them explain why using what they learned from
looking at the apple. Light from every point of the object is traveling in every direction (more or
less), so light from every part of the object is hitting every part of the screen, hence there is no
discernible image. Draw a ray diagram using two points on some object, like a light, a house, or
a window. One point should be at the top, one at the bottom, Rays from each point should go to
(almost) all parts of the screen.
Now switch to the pin-hole cameras. Have the students look around again, at the lights,
windows, whatever. They should cover one hole at a time and compare the images they see.
They should be able to see that the images are upside down, that the image from the smaller hole
is clearer, and the image from the larger hole is brighter.
Now they need to explain it using ray diagrams. Again, the ray diagram should use two points, at
the top and bottom.
The points, again, are that light emanates in all directions from objects (unless they’re black,
there’s no light on them, they’re transparent, they’re completely smooth, etc.), and that light
travels in straight lines (as far as we can see). Light actually bends around objects, through
objects, and in gravitational fields.
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Assessment
Writing Prompts
Relevance
Answers to Exercises
1. Why can everybody who’s looking at an orange see it? [Because light is emitted in all
directions from every spot on the orange.]
2. Does everyone who looks at an object see the same image? [No, everybody sees a different
image. Even your two eyes see different images.]
3. Why can everybody who’s looking at a candle see it, even if there are no lights on? [Because
light is emitted in all directions from the flame.]
4. If light didn’t travel in straight lines, would vision be as useful as it is? Explain using a ray
diagram, but make the rays curve. [Light wouldn’t be as useful if rays curved because then
objects wouldn’t be where they appeared to be.]
Answers to Challenge/ extension
1.
Equipment
Pin-hole cameras are just a light-tight box with a small hole
in one end and a viewing screen on the other end.
Viewing screen – A thin, translucent material makes a good
viewing screen. Plastic grocery bags work well, as does wax
paper. Use a rubber band to hold the screen over the open
end of the camera.
Pin-hole camera – Cut one end out of a tin can. Make two small holes in the other end. The holes
should be near the center of the tin can, about 1 cm apart. They should be two different sizes,
about 1/16” and 1/8”. Drilling makes nice clean, round holes,
but you could make them with an ice pick or nails, too. You
could also make two separate cameras with one hole each. Put
the screen on the open end.
Huge-hole camera – Cut both ends out of a tin can. Put the
screen on one end.
Viewing tube – The image on the screen will be relatively dim.
In order to make it more visible, make a viewing tube to block
out ambient light. Roll a sheet of black construction paper over the grocery bag end and hold it in
place with a rubber band.
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Background
How does light travel from objects to our eyes? How can we all see the same thing? Are we
really seeing the same thing?
Problem
Investigate the behavior of light using a pin-hole camera.
Materials
1
Huge-hole camera
1
Pin-hole camera
1
Ruler
Procedure
Assemble the pin-hole cameras if needed, following the teacher’s instructions.
Look at some bright object, like windows, or lights, or objects outdoors, through the huge-hole
camera. If the light is bright enough, look at a classmate. What do you see on the image screen?
Try to explain it using your knowledge that light goes in all directions from every point on an
object, and that light travels in straight lines.
Now look at the same object(s) using the pin-hole camera. Cover one of the two small holes in
the end of the can, and look at the object, then cover the other hole. What do you see?
Summary
1. What is the orientation of objects seen through a pin-hole camera? Are they upside-up or
upside-down?
a. Using a ruler, draw a ray diagram showing why objects appear in the orientation you see
on the screen. In your drawing, show the object, the pin-hole, and the screen, something
like this:
2. Through which hole in the pin-hole camera do objects appear clearer?
a. Draw two more ray diagrams with different size holes, showing why the objects differ in
clarity.
b. Explain
3. Through which hole in the pin-hole camera do objects appear brighter? Explain.
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Reading
Look at the size of the pupil of your eye or a friend’s eye. Compare that to the size of the holes in
the pin-hole camera. Your pupil serves the same purpose as the holes in the can. Stand in front of
a mirror and look at your pupil. Keep looking at the same spot, but turn the bathroom light off.
Wait a few seconds and turn it back on again. You can see your pupil get smaller when the light
goes on. At night, your pupils gets bigger to allow more light (energy) in so that you can see in
the dark. During the day, your pupils get smaller so that things aren’t too bright for your eyes.
For many people, vision is better during the day than at night. That’s because their pupils are
smaller, so the image formed in their eyes is sharper and clearer. Compare your night and day
vision. If you wear glasses, take them off and try looking at something through a very small hole.
You can make a small hole by putting the tips of your thumbs and two fingers together. The
image should be clearer.
The image in the pin-hole camera was upside down on the screen. Does that mean that the image
in your eyes is upside-down, too? Yes. The image formed in your eyes is physically upsidedown, but your brain turns it over so that down for you is in the direction of your feet.
Light basically travels in a straight line, radiating out in almost all directions from every point on
an object. You can use this simple knowledge to help you understand how light works.
Exercises
1. Why can everybody who’s looking at an orange see it?
2. Does everyone who looks at an object see the same image?
3. Why can everybody who’s looking at a candle see it, even if there are no lights on?
4. If light didn’t travel in straight lines, would vision be as useful as it is? Explain using a ray
diagram, but make the rays curve.
Challenge/ extension
1. Investigate cameras to find out how they work. You may need an old mechanical camera,
even if it doesn’t work.
a) Look at the relationship between aperture and depth-of-field.
b) Look at the relationship between aperture and shutter speed relative to light energy.
c) Why does aperture (f-stop) have a non-linear relationship to shutter speed?
Glossary
 Light ray – a line showing the path light follows
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