calibration, 1st measures, samples
The calibration of the material is a heavy task – but now the system works.
Below are two pictures representing light measurements in RAW mode (linear) on my digital camera, every pixel is made after 1 photo which has been croped and averaged, and they correspond to +- 10 x 10 cm zones of the wall.
The 1st picture has been made with 1/4 sec. aperture, the second with 1/2 sec.
The continuitiy has been reproduced after the pixel values in a spreadsheet program (see below).
It looks pretty surprising, but the Black density of the random-pixel-distribution printed samples placed on the wall corresponds exactly to the correction needed to make a “ganzfeld.”
That means that: THE AMOUNT OF DIFFUSED LIGHT IS STRICTLY EQUAL (well… sctrictly is a big word! :) AT POSITION A, B, C etc.
However, the eye & brains “fight” against these equalities, trying to “tell” that the sample A is darker and B is lighter, even if the amount of light that they redirect in my direction is strictly equal for A & B…