Scanner + Camera Obscura

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We can create a sort of photographic camera with a digital scanner and a camera obscura.

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If we want to focus close objects, we have to build a camera obscura with a sliding part.

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We have built a camera obscura of black foam core cardboard with a base of 20 cm x 28 cm and a height according to the focal length of the lens, 20 cm.

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We are using a bi-convex lens with a focal length of 200 mm and a diameter of 50,8 mm.

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So the height of the camera obscura must be 200 mm = 20 cm. When the sling part is closed, the lens will be focused to the infinity.

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This is what our scanner + camera obscura looks like

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The scanner + camera obscura does not give any visual reference to focus the object, so we have to apply the formulas you can find in the paper: “How to calculate the focusing distance”.

 How to calculate the focusing distance

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This is the formula, where f = focal length, s = the distance from lens to the object (focusing plane) and Δx = the sliding distance.

 If our globe sphere is placed 100 cm to the scanner and the focal lenght is 200 mm = 20cm, the result is 20 X 20 / 100 - 20 = 5 cm

If our globe sphere is placed 100 cm to the scanner and the focal length is 200 mm = 20cm, the result is 20 x 20 / 100 – 20 = 5 cm. The sliding distance is 5 cm.

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With a Canonscan LiDE 35 scanner we got this image (a bright, sharp enough, white and black image).The scanner specifications are:
Scanning Element: Contact Image Sensor (CIS)
Light Source: Three-colour RGB LEDs.

We tried the Canonscan LIDE 35 scanner with a image outdoors...

We tried the Canonscan LiDE 35 scanner with a image outdoors…

But we got this image (too much light for this kind of sensor, we guess)

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Now, we are going to use the formula the other way round. We place the sliding part at 15 cm from the scanner and…

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we apply this formula, where f= focal length= 200mm = 20 cm, and Δx (the sliding distance)= 15 cm. Then, 20 (20 + 15) / 15 = 46,666 cm. So the globe sphere has to be placed 46,6 cm from the scanner.

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With an Epson Perfection 1650 scanner we got this image (a dark but sharp colour image). The scanner specifications are:
Photoelectric device: Colour CCD line sensor
Light source: White cold cathode fluorescent lamp

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The same image amplified

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The darkness of the indoor image made us have a go with a outdoor image

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We fixed a lens hood to protect the camera from the sun

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And we get this image

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The same image amplified

Some further information:

 

 

Sábado, 18 de abril de 2015