The Camera Obscura Project


The idea behind the camera obscura is that an image can be projected onto a surface in a darkened room through a pinhole. The smaller the pinhole, the dimmer, but sharper, the image. In this project the projected image was recorded by a conventional camera using a long exposure.

The Darkened Room (see the attached co-setup.gif drawing)

I decided to use a bathroom because it had only one window. I darkened it by cutting out a piece of cardboard and taping it over the window molding using black, photographic masking tape. The door to the room already had a reasonably dark seal, except at the bottom where I placed a rolled up towel.

The Pinhole

I cut a hole in the cardboard about 2 inches square. I covered this hole with a piece of aluminum foil, taping it in place with the black masking tape. I made a pinhole in the center of the foil using a 16 gage wire nail (0.0508 inch diameter).

The Screen Setup

I taped a piece of 14" x 17" Ledger Layout paper to a piece of cardboard. I hung this from a light stand in front of the pinhole. After waiting 5 minutes for my eyes to adjust to the darkness, I moved the light stand back until I had a decent sized image on the paper. I measured the pinhole-to-screen distance as 36 inches.

The Camera Setup

I placed a 35mm camera on a tripod and located it next to the pinhole, 2’-6" from the screen. The camera (Minolta SRT-100) had a 50 mm, f/2 lens. The camera’s meter was not sensitive enough to detect the image projected through the pinhole. I also tried a Gossen LunaSix 3 meter, but was unable to get a usable exposure reading.

The Exposures

I loaded the camera with T-Max 400 film, open the lens aperture full, and placed the shutter speed on "B." I used a cable release with a locking mechanism to keep the shutter open.

I made 4 exposures: 30 sec, 60 sec, 1 min., and 4 min. I then processed the film in D-76 (Stock) for 9 minutes at 66 degrees F. All exposures showed a bit of an image, with the 4 minute exposure, the best, but still underexposed by what I judged to be about 3 f/ stops. By this time I had lost the sun.

2 days later, for the next exposure I repeated the same setup, but used one exposure of 12 minutes. This time I push processed the film in D-76 (Stock) for 18 minutes @ 66 degrees F. This gave me an approximate film speed of 1000 ASA and yielded one negative with proper density.

The Print

The negative was printed 5" x 7" on Arista #3 RC paper and given normal processing. The print was scanned and the digital image was enhanced only by increasing the contrast about 15% and adjusting the brightness to suit. The image was resized to reduce its file size a bit. Click here to take a look at it.

The image shows my neighbor’s garage. To the right of the garage a flagpole can be seen. There is a large American flag on the pole, but due to the long exposure time and the wind that we were having, the flag, or rather it’s "ghost" is barely visible.

I also noticed some geometric distortion in the window on the side of the garage. I had not expected to see this generated by a pinhole. Perhaps it was from the angle at which my camera recorded the projected image.



Copyright © 1998, Vince Long

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