'Camera obscura' is the Latin term for a dark chamber. This is an optical device that is used to capture the light which is emitted by an object and project it on a screen. This concept was developed 1000 years ago, and it was nothing but a dark room with one hole in the wall. Later it was developed into portable versions, which are called pinhole cameras.
Instructions for Making a Simple Camera Obscura
- Lamp with clear incandescent bulb
- Empty coffee can or Pringles can
- Thumbtack or push-pin
- Nails (which can make a 3 mm hole)
- Opaque tape
- Large rubber band
- Sheet of wax paper (30 cm x 30 cm)
- Thick blanket (through which light cannot pass)
Step 1: Place the can on a sturdy table with the open end down. Using the hammer, punch a hole on the bottom surface of the can with a nail. The diameter of the hole should be approximately 3 mm. Take out the nail and cover the hole with a masking tape.
Step 2: With a push-pin or a thumbtack, pierce a small hole on the tape. Pierce the hole in such a way that, the hole appears directly above the center of the hole made using the nail.
Step 3: Invert the can and cover its opening using a wax paper sheet. Stretch the wax paper tightly on the opening of the can and fix it with a rubber band.
Step 4: Darken the room and switch on the lamp. Stand about 1 m away from the lamp and point the bottom of the can, where the holes are pierced, towards the lamp. The light from the bulb inside the lamp passes through the pinholes in the masked tape and the image of the bulb will be projected on the wax paper.
Step 5: If you are not able to see the image clearly, it could be because the room is not totally dark. In that case, use a blanket or a thick towel, to cover you head and the part of the can which is covered by wax paper.
Step 6: Observe the image of the bulb by slowly moving forward and backward and by varying the diameter of the nail hole.
Use the hammer carefully while punching a hole on the can with a nail. Don't look directly at the sun while using this device. Use only low intensity source of light. It is recommended to conduct this activity under the supervision of an adult.
- The image of the bulb appears upside down and dim in intensity.
- The image of the bulb on the wax paper varies according to the viewing distance. As we move closer to the bulb, the image appears bigger.
- By increasing the diameter of the hole, it is observed that the image becomes brighter but not sharp.
Inside the Dark Chamber
Light from any object travels in straight line in all directions. In our experiment, the light rays from the bulb hits the bottom of the can, but most of the light rays are blocked, because of the coverings of the tape. Few light rays travel through the pinhole and they appear inverted on the screen.
The reason why they appear inverted is because, the light rays are crossed in space as they pass through the pinhole. After piercing a larger hole, the image appears large and distinct, because more light rays fall on the screen due to increase in size of the hole. But the image became fuzzier because of more interference between the light rays.
The image of the object can be made better by using lens instead of pinholes. The focal length of the lens is equal to the distance of the lens from the screen. The diameter and the focal length of the lens should be changed proportionately, to get adequate brightness of the object.