All About Photography

The maximum and minimum focal ratio of the eye is more limited than a normal lens (f3.3 – f15 versus f1.8 – f22) but this is more than offset by a broad ISO range (1-800 ISO versus 100 ISO 3200 in a typical digital SLR). In addition, the dynamic range of the eye is infinitely superior: 1:10.000.

Instead, the shutter speed of the eye is single (1 / 100 sec.) which has an evolutionary point of view is perfectly adequate, but the camera clearly has more options (such as very fast shutter speeds, which allow you to freeze movement, something the eye can not do, or the opposite extreme, long exposures required to build light and see what is invisible to the eye).

And what about the sensor ? Well that’s where the difference is enormous: it is quite large (like a digital back CCD) and has pixels of similar sizes, but has a resolution equivalent of several hundreds of mega pixels, although this parameter is not exactly comparable: a point, the eye only processes a fraction of the total visible area, the rest remains out of focus black and white!

Let’s see a possible example: The human eye, on a sunny beach, with a shutter speed of 1 / 100 sec. to f11 and an ISO of 12 (and a resolution of, say, 350 Mpix.). The exposure equivalent of a digital SLR camera (of say 12 Mpix.) would be: f16, 1 / 500 sec. and ISO 100. This of course is only a theoretical calculation since all these parameters are not exactly comparable in reality or equivalent …

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