237-
The Technical Cornerstones of Photo-Interpretation (Fig. Ts left).
It is common practice in textbooks and lectures to compare the
EYE with a CAMERA - unfortunately, because here too the danger is
all too real that the teacher and the pupil both miss the essential
character of the eye. Moreover, it reveals the characteristic short-
comings of conventional educational systems, or isn't it a pity that
we know a camera better than our own eye? Here are some characteristics:
: The eye's white light sensitivity should not be compared with a
photophotographic emulsiony but with all panchromatic emulsions
through the whole DIN or ASA range, as the retina automatically
adjusts its sensitivity to comfort the illumination, from bright
é daylight (1ow sensitivity) to complete darkness (almost).
The ultimate "speed" of the human eye is limited by ihe statistical
nature of light itself. As the modern secondary school book
Physios (1960 Par. 33-2) states: "It is striking that the effects
of the intrinsic graininess of light have been demonstrated to
occur for the eye just about at the dimmest light which a man can
see.
Our eyes are developed about as far as any light receivers
working with the same size of lens, the same time of response,
and the same of wave lengths can possibly be. They have reached
very close to the natural limit."
$8 Indeed, for a fair comparison, the exposure time of the eye
(0.1 sec is the maximum integration time, down to 0.02 sec?) and
the relative aperture have to be known (the pupil's diameter
over the focal length = 3:15 for normal conditions, 75:15 for
dark adaptation at maximum, so 134.5 to 1:2).
: The eye's Imaging Quality is comparable with a good camera-
V e -objective, but again, the quality at the corners is much better
in a camera (a fact which does not keep us from claiming for still
better).
: However, for compensation, the eye scans in all directions and
works so to say always on its optical axis (as the Old Delft
concentric optical systems, where all centres of curvature coincide),
? This is also the reason the large distortion is not noticed,
although ihe eye has a rather extreme wide-angle effect, This is
/CCHNLCA/ Cornerstones Of ("5000 Jpterpretacteo»n
due to the fact that each nerve to the brain serves
CAMERA \ one rod at the central retina, and an increasing
Sensitive number of rods and cones near the periphery. The
msiti
Eus central portion of the picture needs in the brain
«Ll. Qva. ; xi : ; i
— i more storage space than the edges — as in an extreme
Contrast wide-angle camera, where the scale is substantially
Sbectrym A
x "A smaller near the edges.
Ni A
