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15.5 Eye and the Camera
The decline is rapid after that.
The near point is shifted to 100 cm at age 60.
There is a lens system that focuses a real inverted image onto a photosensitive surface.
In the camera, the diameter of the light entrance is controlled by a diaphragm that is adjusted in accord with the available light intensity.
In a camera, the image is focused by moving the lens.
The distance between the retina and the lens is fixed in the eye, while the image is focused by changing the thickness of the lens.
The photosensitive surfaces are similar.
Both photographic film and the retina have light-sensitive units that change in size when illuminated.
Under special circumstances, the retina can be developed to show the image projected on it.
The first demonstration of this was in the 1870s.
The rabbit's eye was exposed to light through a barred window.
The barred window was not visible from the outside.
A guillotined criminal's eye was fixed by Kuhne a few years later.
He couldn't see anything that the man had seen before he was beheaded.
The eye and camera analogy is incomplete.
The eye goes far beyond the camera to process the images projected on the retina.
The size of the iris depends on the available light.
The quality of the image is best if there is adequate light.
It's true for both the eye and the camera.
There are two main reasons for the improved image.
The edges of the lens tend to have flaws.
The light path to the center of the lens is restricted by a small aperture.
The image quality of objects that are not located at the point on which the eye or the camera is focused can be improved by a smaller lens.
An image is in focus only for objects at a certain distance from the lens system.
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