A fascinating exercise showing the camera’s ability to detect very subtle changes in the scene before it. The images below were taken at 30-second intervals, using a tripod to ensure identical framing.
This was a ‘cloudy bright’ day with the sun behind a cloud for all four exposures. There was a slight breeze, so I avoided plants with moving leaves (which would be too easy to interpret) in favour of a subject that appeared static.
Technical information: all images were shot on an Olympus E-30 set to fully automatic mode. Image capture was JPEGs, medium-resolution normal-compression. The metering has taken all four images at 1/80, f/4, ISO200
All four images appear identical at first sight. I collected all four as tabs in a single Photoshop window, which allowed me to quickly switch between them and detect differences as ‘jitter’.
There is a subtle change in the light between the first and second images; shadows below the chairs become slightly darker and cooler. The twigs in the rear container shift slightly between the second and third frames (probably a breeze). A piece of twine on the rear trellis hangs directly in front of an upright in the third frame (a white section of wire disappears – this took a while to understand). A small leaf moves from right to left through the second, third and fourth frames.
I obtained histograms by importing all four images into Camera Raw and taking screenshots. Some surprisingly large changes can be detected by my ‘collect-and-jitter’ technique.
I have stacked the histograms together (in the same order as the images) for ease of comparison.
The changes most noticeable relate to the shape of the blue peak and the details in the colour fringes on both ‘shoulders’ of the graph.
An interesting point is that the histogram changes are more obvious than the changes in the scene itself. Whether this is due to the sensitivity of the camera as a measuring instrument, or to random fluctuations of the automated metering algorithms, is unknown at present. It would be interesting to repeat the exercise using all manual settings to bypass the automation as far as possible.