The Human Eye
The human eye has some similarities with the camera (we made a parallel between human eye and camera in this article). The eye, wanting to schematize to the extreme, it can be seen essentially as a sealed container of light contained within the sclera, having a lens system composed of the cornea and the lens which concentrates the rays of incoming light on the retina positioned in the the back of the eyeball, to form an inverted image. The iris controls the amount of light entering the eye: when fully open (in low light), the iris has a diameter of about 8 mm while in a condition of high brightness is reduced to about 1.5mm. The iris has openings equivalent ranging from f / 11 to f / 2 and a focal length of about 16 mm. The retina comprises a thin layer of cells containing the photoreceptors sensitive to light.
The electrical signals from the light-sensitive receptors are transmitted to the brain via the optic nerve. The light-sensitive receptors are of two types (rods and cones) and are not distributed evenly across the retina, as shown in Figure below akusaraprosound. The rods are sensitive to low levels of light (scotopic vision, night vision) and cones are sensitive to high levels of light (or photopic, daytime vision). In addition, the cones are responsible for color vision and perception of forms.
As can be seen from the graph, the amount of rods is particularly high, just as there is a blind spot, the point where the optic nerve is physically connected to the optician (and therefore devoid of both rods which cones). At the center of the retina is the fovea positioned which is the most sensitive area of ??the eye, the size of approximately 1.5 mm diameter are crammed in which the largest number of cones, over hundred thousand.
The mechanisms of vision involving the organization of receptors, the complex ways in which the signals are generated, organized, processed and transmitted to the brain will not be taken into analysis in this article I want to be a general understanding of all that level physical can affect the photograph. Including, therefore a whole range of visual phenomena that have been studied extensively and have a series of consequences in the understanding and evaluation of photographic systems “mechanical”.
The human eye: the light and dark adaptation
When you switch from one environment to a dark room lit or dimly lit, the room itself appears instantly darkened. After about 30 minutes, however, the visual system adapts to the situation, through the use of cones use of rods, thus allowing us to see in the dark. Conversely, in going from a dark to a particularly bright, the eye adapts in about 5 minutes, back to using cones.