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.
To fulfill the requirements of this exercise of taking three to four images in quick succession using the cameras automatic setting, I walked to the top of Salisbury Plain with my Lumix DMC-GX7 camera. It was a pleasant day with a slight breeze, the clouds were beautiful and I rather hoped that the wind would pick up and I would see some rapid changes in the histogram of the three shots I took. Alas, this was not to be and the breeze remained light.
I set the camera to iA (Intelligent Auto) and using the kit lens of a Lumix G Vario 12-42mm I zoomed to a focal length of 24mm to reduce the amount of grass in the foreground. On reflection I could have reduced this even further but the “Rule of Thirds” is relatively well demonstrated in the shots. The histograms show that all three shots are reasonably well exposed with with a broader tone distribution in the mid-tones section and no clipping of the highlights or shadows.
The dynamic range of the shot was limited with not a lot of contrast apart from the dominant white cloud. Even in the first shot it is evident that there is a breeze because the grass in the foreground is very slightly blurred due to movement in the breeze. However, the biggest change was the RGB percentages between the first and second images, whilst the third image showed slight changes they were not as significant as those between image 1 and 2 but less so between 2 and 3. This suggests that there was less light getting into the camera in the first shot.
Image 1 with Histogram
In image 1 the RGB percentages are around 60% across the sky and there is an even distribution of tones across the histogram
Image 2 with Histogram
The RGB percentages across the sky change significantly in Image 2 to around 88%
Image 3 with Histogram
In the final image the sky RGB percentages are in the lower 80%
The corresponding RGB percentages for the grassy area show similar changes and suggests that the clouds are moving and the effect is less or more light getting into the camera.
The peak to the left of the histogram suggests that the shot maybe slightly underexposed. Experimenting in Lightroom 5 by increasing the exposure does not improve the shot and serves to begin to blow out the highlights with a certain amount of loss of contrast.