Take three or four exposures of the same scene. Don’t change anything on the camera and keep the framing the same.
Preview the shots on the LCD screen. At first glance they look the same, but are they? Perhaps a leaf moved with the wind, the light changed subtly, or the framing changed almost imperceptibly to include one seemingly insignificant object and exclude another. Time flows, the moment of each frame is different, and, as the saying has it, ‘you can’t step into the same river twice’.
Now bring up the histogram on the preview screen. The histogram is a graphical representation of exposure – the camera’s sensitivity to light. As you page through the images you can see small variations in the histograms. Even though the pictures look the same, the histogram data shows that in a matter of seconds the world changes, and these subtle differences are recorded by the camera. If you refine the test conditions – shooting on a tripod to fix the framing, moving indoors and closing the curtains to exclude daylight – still the histogram changes. Probably some of the changes are within the camera mechanism itself; still, the camera is a sensitive enough instrument to record them.
Add the sequence to your learning log with the time info from your camera’s shooting data as your first images for Part One.
For this exercise I took three shots near my house using my Canon EOS 5D mkIII with a Tamron 28-75mm lens. I chose ISO 100, 1/200 f/5.0. I took the shots immediately after each other as a van passed on the main road.
Whilst I thought I’d held the equipment steady, I’d moved the camera down a bit on pressing the shutter. I should have used a tripod to ensure the frame was identical for all three shots.
In terms of the content changing, the van is seen moving up the slight hill. Due to the frame movement, it’s difficult to spot if there’s any movement of the trees.
Looking at the histogram analysis outputs via RawDigger, there are slight differences across the spectrum between all three images – this is unsurprising considering the moving van and frame-shift.