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This is one of my matchbox pinhole cameras. It takes 35mm film and is very easy to build and use.
alspix has a great tutorial.
Worldwide Pinhole Photography Day is April 29th this year. You still have plenty of time to prepare. There is lots of interesting info on
Without Lenses, including a great
video by
Nancy Breslin about pinhole photography.
The Populist, designed by Nick Dvoracek, is another pinhole camera that takes 35mm film.
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If you have access to a darkroom, you could make Stewart Woodruff's
oatmeal box pinhole camera that takes light-sensitive photo paper.
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Here's another camera that takes light-sensitive photo paper, and probably took me 20 minutes to make.
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Here's a part of my pinhole camera collection. This photo is on Camera-wiki's
homemade pinhole camera page.
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Here's my entry for last year's WPPD. Taken with
Tyrannosaurus photo ventris.