Photographs
The above was a two-hour exposure (near midday). All three were taken when the subject was illuminated by direct sunlight (in April, around 40°N latitude) and the camera was outside — that is, had no glass but the lens between the Diazo paper and the subject. The paper is about 23x27cm (9x10½in).
Two-hour exposure, some clouds, mid-morning.
One and a half hours, late afternoon.
Introduction
The above are photographs made on Diazo paper (also called "whiteprint" paper; similar to blueprint paper). They were exposed in a simple camera I made; I also made photographs on Diazo paper with my co-workers, using various other cameras.
The camera looks like this:
The ice cube trays are to adjust where the camera is pointing. The tiles are to keep it from moving (since it was a windy day).
Diazo paper exposes with ultraviolet light; I have used sunlight to make exposures. Loading the camera in an unlit room during the day seems safe; and incandescent lights do not produce ultraviolet light (though flourescents do produce some).
Developing
Diazo paper develops by reacting with ammonia vapor. Although Windex contains some ammonia and will develop images, it is faster — especially with large pieces of paper — to use ammonia cleaner.
The paper starts solid yellow; exposure to UV turns it white. This is an exposed but undeveloped paper:
This is my developing container (closed, and open with the ammonia I used):
I crimped two sheets of aluminum foil together to make an airtight envelope. I put a little ammonia in a plastic tray, put a few cut pieces of sponge on the tray (to aid evaporation), and then put a few sections of plastic bottles on the tray to hold the paper above it.
An image develops in about 20 minutes.
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0 minutes |
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6 minutes |
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12 minutes |
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20 minutes |
The above developing setup sometimes warps the paper, since it becomes damp while developing and is supported unevenly; broader and more even support might be better.
Camera Construction
The camera is made of two matching boxes with flaps taped open. I trimmed the front's flaps slightly, to fit inside the back's flaps.
The boxes are 29cm wide x 29cm high x 35cm deep. (20.5cm deep without the flaps opened out.) The front box's flaps taper to 27.5cm wide/high where I trimmed them.
Materials
- two matching corrugated cardboard boxes
- 2 dioptre 77mm lens from a macro lens filter kit
- black duct tape
- black construction paper
- cinefoil (same purpose as black construction paper)
- lightweight cardboard
- Elmer's glue
- double-sided tape
I cut a small door into the front, next to the lens, for a viewfinder. I put a section of cinefoil on the bottom side to reduce reflected light from the sky which strikes that side. I put flaps of tape on the outside sides, to use as handles when pulling the camera open.
I mounted the lens in a hole with cardboard to hold it in place. I glued the two layers of the box's flaps together, then cut a hole through both layers which was slightly smaller than the lens in the back layer. Then I cut a hole in a piece of tagboard that was slightly smaller than the lens, and taped that in front.
I put black construction paper around all sides of the back to reduce reflected light from bright objects just outside the exposure area. I put a few small pieces of double-sided tape on the back wall to hold paper in place while making exposures.
Looking through the viewfinder door while the camera is set up (note that I've rotated the image 180°; it appears upside-down):
Camera Properties
F Number
The f number of a lens is its focal length divided by its diameter (explanation by Matthew Cole). The focal length of a lens (in meters) is 1/dioptre (see Wikipedia).
I used a 77mm, 2 dioptre lens. 77mm = 0.077m. 2 dipotre = 0.5m focal length. The lens is therefore approximately f/6.5.
(As expected, when focused at infinity, the camera's exterior length is 52cm. To focus at 3 meters (10 feet), I slide it out to be 60cm long.)
ISO of Diazo Paper
Knowing the exposure time and aperature, we should be able to calculate the ISO of Diazo paper. This may help with predicting required exposure time, though a visible-light camera or light meter won't match the UV-exposed Diazo paper necessarily.
Exposure varies with N2/(S * t) (if I understand exposure acc. Wikipedia correctly). Here N is f-number, S is ISO film speed, and t is exposure time in seconds.
I took two images similar in exposure to the two-hour exposure above, for help in calculation.
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ISO 100, f/22, 1/30s |
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f/6.5, 7200s |
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ISO 100, f/22, 1/15s |
Using the 1/30s photo to calculate the scene's exposure, it seems Dizao paper is about ISO 4E-5 (.00004).
However, using my dSLR as a light metering tool, it is more usful to find the proper exposure at ISO 100 and f/22, then multiply exposure time in seconds by 60 to get exposure time in hours for the box camera.