Making And Using A Simple Camera Topic Observing light passing through a small aperture
Introduction The first cameras consisted of a light-proof box with a tiny hole at one end (the side facing the subject) and a light-sensitive screen at the other. This arrangement had been found to allow just enough rays of light from the subject of the picture to enter the box to form an image of the subject on the screen. Photographers in the early 19th Century had to cover their heads and their equipment with a dark cloth because the image was so faint and difficult to see. In this experiment, you will make a simple camera and then use to observe a subject (a lighted candle) on a screen in a darkened room.
Time required 20 minutes to construct the camera (plus time for the glue to dry) 30 minutes to use the camera
Materials For Part A: template for camera (see diagram 2 on page 4.06–4) 1 8 /2 × 11 sheet of dark poster board glue scissors masking tape sheet of waxed paper (8 × 10 cm) straight pin
For Part B: double convex spherical lens with focal length of 10 cm pencil some small pieces of dark poster board (about 2.5 cm square) candle in a candleholder matches 30 cm ruler pencil paper
Safety note Be careful when using the scissors to cut out the camera shape and to score along the folding lines. Be very careful when using the matches (or gas lighter) and when the candle is lit. Ensure that a fire blanket is available. Pull back long hair.
Procedure External light does not to need be excluded during this experiment.
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Part A: Making the pinhole camera 1. Make a copy of the camera template and glue it to the card. Allow the glue to dry. 2. Cut out the camera shape along the straight solid lines (but not the circle). 3. Score the poster board using the scissors and fold the card along the dotted lines. 4. Tape the sides together to form an open-ended box with the lines on the template showing on the outside. 5. Tape the piece of waxed paper over the open end of the box. This forms the “screen.” 6. Using a pin, make a small hole in the center of the marked circle. Part B: Using the pinhole camera 1. Pull back long hair and put on your safety glasses. 2. Light the candle using the matches. 3. Place the candle 20 cm from the pinhole of the camera (see diagram 1 below). Direct the pinhole at the flame while observing the screen until an image of the candle flame is seen. You can either hold the camera or support it on the table (whichever is more convenient), but make sure you don’t move the end of the camera into the flame. 4. Draw the image you see on a sheet of paper. Label open end of the sheet “single pinhole”
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box pinhole waxed paper
candle 20 cm candle holder
Pinhole camera and lighted candle
5. Observe the image of the flame while moving the camera closer to and further away from the candle flame, looking at the screen. Make sure you don’t move the end of the camera into the flame. 6. Turn the camera towards you and use the pin to make four more pinholes around the original pinhole in the circle on the front of the pinhole camera. 7. Observe the image of the candle flame and draw it on your sheet of paper. Label the sheet “fine pinhole” 8. Using the point of a pencil, join the five pinholes to make one large hole in the circle at the end of the camera (about 4 mm in diameter).
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9. Observe the image of the candle flame and draw it on your sheet of paper. Label the sheet “large hole” 10. Hold a convex lens in front of the hole and observe the image on the screen as you move the lens between the candle and the camera. Draw the image seen. Label it “with lens” 11. If you wish to repeat any part of this experiment using a smaller hole than there is in your camera, cut out the circle on the front of the camera and place one of the square pieces of poster board over the circle and tape it in place. You can then make a new pinhole.
Analysis 1. Is the image of the candle flame upright or inverted? 2. Is the image sharply focused at all distances of the candle flame from the camera? 3. Is the image larger when the candle flame is closer to the camera or does it stay the same size? 4. Describe the image formed by five pinholes in the camera. Is the image brighter than the image produced by the single pinhole? 5. Describe the image formed by one large hole in the camera. Is it more or less clear than the image formed by the single pinhole? Is the image more or less bright than the image formed by the single pinhole? 6. What is the appearance of the image when a convex lens is held in front of the camera?
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PHYSICS EXPERIMENTS ON FILETM
LIGHT • 4.06–4
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10.21 • OUR FINDINGS
Object
PHYSICS EXPERIMENTS ON FILETM
Color of shadow
Colors absorbed by the object from the white light from the flashlight
red
red
green and blue
green
green
red and blue
blue
blue
red and green
yellow
yellow
blue
magenta
magenta
green
cyan (turquoise)
cyan (turquoise)
red
4.06 Making And Using A Simple Camera 1. The image of the candle flame is inverted. The reason for this can be seen in the diagram below. Rays of light travel in all directions (in straight lines) from the candle flame. A ray of light from the top of the flame travels through the pinhole and continues to travel in a straight line until it reaches the lower part of the screen. Similarly, a ray from the base of the flame travels through the pinhole, crossing over rays from the top of the flame at the pinhole and continuing in a straight line until it reaches the upper part of the screen. pinhole camera pinhole
light spreads out in all directions
faint inverted image of candle flame on screen (waxed paper)
candle
candle holder
Image observed using the pinhole camera
2. A sharply focused image is obtained for all distances between the candle and the camera. 3. The image becomes larger when the camera is closer to the candle flame. 4. When there are several pinholes, several overlapping images of the candle flame appear on the screen. Each image is the same size as the image formed by the single pinhole. The number of images formed is equal to the number of pinholes. The net result of the multiple images is to make the screen appear brighter. This is because more light is able to enter the camera. 5. When there is one large hole in the camera, the image on the screen is less distinct but brighter. This is again because more light is able to enter the camera. 6. When the lens is held in front of the camera, the image on the screen becomes clearer. It is bright because the large hole allows more light through than the single pinhole. © Diagram Visual Information Ltd.
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