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Teach yourself and your kids about optics. Have a magnifying glass, a fridge soda box, a paper tube, and some tape? It takes about 30 minutes to throw it all together & project images of the world around you on to a diffuser screen you make yourself.
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Soda Box Camera Obscura
With Real Lens and Frosted-Tape Screen – Easy!
Gregg Favalora – Arlington, Mass.Rev 00 (April, 2010)
http://www.greggandjenny.com/gregg
Pick a Lens
Find a magnifying glass which:
(1) You can disassemble,(2) Is about 2-3” (5.0-7.5
cm) in diameter;(3) Makes a decent-
quality of a distant object (house outside, ceiling lamp) when the lens is held about 12” from a surface.
Far away
About 12”(shorter thansoda box)
When I did it, it looked like this
It is difficult to photograph, but my lens made an image of our ceiling lights when I held the lens about 12-18” above the table.
FOCAL LENGTH:
The distance from the lens to the image is the focal length of the lens, if the distance from the lens to the object is very very far away. An example of this would be making an image of the house across the street, as seen through the window from inside your house.
White Paper
Image of ceiling lights
Push-Pull Lens Tube
Tape the magnifying-glass lens to the end of a paper towel tube. Align the top of the lens to the top of the tube.
Tear a notch out of the pull-tab of the box, and tape the lens-tube subassembly into it.
Now you have a push-pull lens tube.
Make the filmless viewing screen
Make the viewing screen:
1. Get some diffuse tape, like Scotch-brand Magic Tape.
2. Stretch several columns of it, overlapping, to make a screen.
3. Better yet, use drafting Vellum.
4. Or experiment with other materials, like tracing paper or tissue-paper.
DIFFUSER
This screen lets you see the image because it scatters incoming light to many angles, some of which reaches your eye. “Magic tape” will let you see the imagery from a decent range of angles. Other materials have different light-scattering capabilities.
Overlapping flat columnsof diffuse tape (like ScotchMagic Tape). Or, better, drafting Vellum.
Cut a Notch in the Box
Insert the Lens Tube
The Finished “Camera”
Place the push-pull focus tube into the open face of the soda box.
Carefully point the tube so that it’s in line with something bright and interesting, and then pull or push to focus an image of it on the tape screen.
The Camera in Action
The Camera in Action
Remember to slowly push or pull the lens-tube until the image comes into focus.
The lens creates an image of the “object,” which in this case is the television screen.
We were watching “Martha Speaks.”
Image of Television Screen
What do I look at?
Best if the room is dark Look outside the window; make a
picture of the house across the street. On ours, it is bright and full of color.
At night, you can image the streetlamps outside
Do NOT stare at the sun (it will damage your vision) and do NOT make an image of the sun (it could burn the screen).
Learning:(image: Wikipedia)
Can you convince yourself that:
If you had been forming an image of something close, like a lamp in your room, then:
…if you want to “take a picture” of something far away, you should push the lens-tube in, so that it is closer to the screen? The image would appear at or near the focus of the lens.
Or:
…an object at twice the focal length will generate an image at twice the focal length?
Have fun!I hope you learn more about the exciting things you can do with light.Gregg Favalora: [email protected]
Photo: Sara Forrest
http://www.physics.metu.edu.tr/~bucurgat/ntnujava/Lens/lens_e.html
http://www.mtholyoke.edu/~mpeterso/classes/phys301/geomopti/twolenses.html
http://g-fav.blogspot.com/2009/02/good-enough-synthetic-aperture.html
Try these:
