I especially love the sharper ones of the city. I'd really like to know how they kept the shutter open for 3 years and still have the photograph at mid-exposure. I would expect the shots to be either to bright or too dark.
Very small pinhole, long tube... he must have had things machined to a pretty strict tolerance and based the length of the tube and the size of the hole on some calculation that takes into account the length of the exposure. Mathematically and mechanically probably pretty straightforward; what really amazes me is how he managed to keep his camera stationary for three years!
ISO 0.25? Heh, I'm sure the lowest ISO feasible-- but with a long tube and a small aperture, apparently ISO is not a limiting factor if the guy could technically manage a 40-year exposure...
Remember that stops are a doubling of time so at these lengths you don't have to be super accurate. If the proper exposure was really two years, you could accidentally leave it open three years and be off only about half a stop.
Neutral density filter?
Looking at the sun trails in the first image, I can see where this technique would be a good way to record the times when the sun was behind clouds for a scientific study.
"Oh, there is that camera that I lost a couple of years ago. I wonder what's on the film? "
There are certain situations where the length of the exposure won't create an overexposed image. If the aperture is small enough, like with a pinhole camera, daylight might not be bright enough to overexpose much of anything, even over an extended period of time. You can create this situation with a standard camera on a tripod by going into a dimly lit area at night and shooting an hour long exposure, or even two hours long. Unless there are really bright areas in your scene, you might not overexpose much of anything. Using a small aperture like f/16 or f/22 would further reduce the exposure level.
I remember reading about someone who did year-long exposures of the NYC skyline. He nailed his cameras to stationary things where people wouldn't see/bother them. Can't remember his name though.
As these are pinhole photographs and VERY long exposures, they probably aren't using film at all. You get an image like this by directly exposing a piece of black and white photographic paper. Paper is much less sensitive than film. Also, you don't develop the paper as you would to produce a photograph from an enlargement or even a paper negative from a more traditional (regular exposure) pinhole camera. The image renders without having to chemically process it. The catch is that you typically have one shot at scanning or reproducing it, as the light will ruin the image in a matter of minutes (opinions are mixed as to how effectively you can fix the image to preserve it).
Way back in the Silver Darkroom Ages, I found that I could easily make a negative image by making a contact print from a B&W photograph. I put the original print on the easel on top of a sheet of photo paper and illuminated it using the enlarger, as you would normally do for a contact print. It worked very nicely. I used Agfa paper for the original print because it didn't have the logo imprint on the back side.
Today's alternative would be to just develop the original made with photo paper, copy it digital, and invert it to negative, which would render it correctly.
As these are pinhole photographs and VERY long exposures, they probably aren't using film at all. You get an image like this by directly exposing a piece of black and white photographic paper. Paper is much less sensitive than film. Also, you don't develop the paper as you would to produce a photograph from an enlargement or even a paper negative from a more traditional (regular exposure) pinhole camera. The image renders without having to chemically process it. The catch is that you typically have one shot at scanning or reproducing it, as the light will ruin the image in a matter of minutes (opinions are mixed as to how effectively you can fix the image to preserve it).
