It is very easy nowadays to manipulate images digitally, and whether we are looking at a magazine or the latest film at the cinema, we know there is likely to have been a lot of digital manipulation of the images that we see.
This article is about a particular type of illusion that was actually created 'in the camera', back in the days when cameras used silver emulsions as the method of capturing images. In order to take an image, the shutter had to open, in order to allow light to fall onto the negative. There were different shutter mechanisms, but a common mechanism was the so-called focal plane shutter, which was placed just in front of the photographic negative. Typically these involved a slit moving across the negative. Often you would want the slit to move quickly, so that you got a short exposure, allowing you to freeze the action. However there was a particular camera which was used for taking group photographs, where the slit moved across the negative quite slowly. At the same time the camera panned left to right, allowing you to capture a very wide group without needing a wide angle lens. I well remember this type of camera being used to take photographs of school groups back in the 1960s.
Now because it takes some time for the camera to pan from the left hand side of the group around to the right hand side, it allows a person to appear in the photograph more than once! Basically, if you are placed at the far left hand side of the photograph, you wait until the camera has moved off you, and you then drop down behind the group, run round to the other end, and pop up quickly, ready for the camera to capture you again as it reaches the right hand side of the group. When Tim was a student at King's College London back in the 1960s, he posed for a departmental photograph where one of the students did just that, as Tim demonstrates in this film.
The famous photographer Robert Doisneau (1912 - 1994) used a camera where the slit moved not only vertically but also very slowly, in order to capture this dancing couple who had been placed on a turntable. As the photograph was taken and the slit slowly moved across the negative, the turntable was rotated. As a result, the couple have rotated 360 degrees between their feet and their heads, and have also become impossibly entwined.
Finally, this picture was taken by the photographer Jacques Henri Lartigue in 1912. It shows a racing car passing a small group of spectators. He was also using a camera where the shutter moved from top to bottom. The distortions are fascinating, and are part of the charm of the image. However the man who is watching from the side of the track seems to be leaning to the left, while the wheel of the car is distorted over to the right. What is happening here? In fact, Lartigue is panning his camera from left to right, and this movement, in conjunction with the moving slit, is causing the man to appear to lean to the left. But it seems that he is not panning fast enough to keep up with the car, which is therefore moving to the right while he is making the exposure. Therefore the wheel of the car leans over to the right. An extraordinary picture, where much of the power derives from these distortions created within the camera.
Here is a site that explains the Lartigue photograph in more detail.
And this site talks more about the distortions that can be created with focal plane shutters.