Monday, 6 January 2014

Ghostly figure mystery

Red hooded ghostThere is something distinctly odd in this photo (right) of a transparent red hooded ghostly figure. And this is the mystery. If you look carefully, you'll notice that both the ghostly figure, and the buildings behind it, look noticeably clearer than objects elsewhere in the photo. It is almost as if the ghostly figure is acting like a lens, focussing the objects behind.

OK, it's not really a ghost but there are many photos like this one which some people believe do show actual ghosts. It is an odd idea because, the vast majority of ghosts are reported by witnesses to look perfectly solid and normal. I have long suspected that the origin of the widespread idea that some ghosts are transparent comes from the theatre and Pepper's Ghost. It is also a widely used convention to show ghosts as transparent in movies (presumably so that the audience realises what they are). This is despite the fact that there is very little evidence for transparent ghost from real cases.

There are other reasons why people seeing a transparent figure in a photo they've taken might think it's a ghost. Firstly, such transparent figures arise from long exposures and the photographer is often not aware they've taken such a shot. Luckily EXIF data is now available and, in the many such photos I've looked at, it is always a long exposure. Secondly, the photographer may not notice anyone present at the time they took their photo. However, it is quite common for someone concentrating on taking a photo to not notice someone drifting into shot. Thirdly, people often think that if a someone walks through a shot during a long exposure, they should show up as a continuous blur, not a stationary transparent figure.

I recently did some experiments concerning this last point. It confirmed my previous experience that moving objects in long exposures only show up if they move very slowly or stop altogether. So, in one shot I got someone to walk slowly straight through a long exposure without stopping and they barely appeared at all. There was just a slight, highly transparent, impression of a boot, like a faint shadow! When the person started stationary and walked out of shot during the exposure, they appeared stationary but transparent. This was how the example here was produced. The same person even appeared twice, both times transparent, in the same shot if they walked slowly enough. When they moved really slowly, they did indeed appear as a continuous blur, as you might expect. If someone was originally outside a frame and then walked into it half way through an exposure and stopped, they would appear as a clear transparent figure. It is this last scenario that probably explains many ghostly transparent figure photos. So, overall, I think the idea of transparent figures in photos being ghosts probably arises from theatrical convention and a misunderstanding of what long exposures do to moving objects.

But why do the buildings look clearer through the ghostly figure in the photo? Well, it was a hand held long exposure which explains the motion blur in the general scene. But the figure and the buildings behind it were each only exposed for around half as long as the overall frame. Thus they suffered only half as much motion blur! You wouldn't get this effect if the camera was on a tripod.

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