Saturday, March 12, 2011
What causes the glare in the picture above? Is it true that:
Glare happens because not all light that hits a lens is focused onto a camera's sensor. A small fraction is reflected inside the lens, emerging in unpredictable places. If a light source is bright enough, this effect can bleach out parts of an image.
Or is it caused by diffraction around the edges of branches:
The apparent bending of waves around small obstacles and the spreading out of waves past small openings.
It might be caused by other effects like overloading of the sensor or reflection of the light on leaves and branches. Marcel Minnaert knows and describes the effect:
It seems as if the setting sun causes an indentation in the line of the horizon.
He calls this phenomenon "irradiation" and cites Leonardo da Vinci who described the effect in his notebooks:
Leonardo da Vinci; in his writings, says of this phenomenon: 'We can see this when we look at the sun through bare branches of trees. All the branches in front of the sun are so slender that one can no longer see them, and the same with a spear held between the eye and the sun's disc, I once saw a woman dressed in black with a white shawl over her head. This shawl seemed twice as broad as the darkly clad shoulders. The crenels in the battlements of fortresses are of exactly the same width as the merlons and yet the former appear to be appreciably wider than the latter.'
Unfortunately his explanation is not very clear and I omit it here. I cannot find the term "irradiation" on the Internet and the term "glare" does not help much. I have searched most of the evening but have not found one convincing explanation. Neither have I found the Da Vinci quote in his notebooks.
The future of photography - NewScientist
Diffraction - Wikipedia
The Notebooks of Leonardo Da Vinci - Wikisource
M. Minnaert - The Nature of Light and Colour in the Open Air - Dover Books on Earth Sciences