There are some similarities between the camera and the human eye. Both have a lens, shutter, and light sensitive material. In the eye, the image is formed by a combination of the cornea, the aqueous humor, and the lens. The eye-lid is the shutter, and the retina is the light sensitive material. The other similarity is that both cameras and the eye control the image brightness by means of an iris diaphragm. In the eye the amount of light is involuntarily controlled by opening and closing the iris. A camera controls the light transmitted through the lens by means of the aperture diaphragm.

But comparing the eye and the camera with one another by stressing only the similarities in their construction has confused the understanding of photography, because it disregards the differences in their function. These differences make the eye superior to the cameras in some instances, and the camera superior to the eye in others.

• Human vision is binocular and stereoscopic, that of the camera is monocular. This is why photographs lack the same “depth of field” that is seen through the human eyes. A camera sees a scene without depth, and a photograph appears flat.
• The eye’s view of the world is subjective, viewing what the mind is interested in, has a wish to see, or is forced to see. The camera sees objectively, recording everything in its field of view. This is the reason so many pictures, are just pictures, full of superfluous subject matter.
• The eye is sensitive to colour. Cameras and different lenses can see colour differently, and black-and-white photography sees colour as shades of gray (the transformation of colour to gray is also varied).
• The eye does not normally perceive minor changes in the colour of light. Both film and sensors are sensitive to such small changes. This failure to detect changes in light colour manifests itself in what the eye considers “unnatural” colours.
• The eye cannot “store” and combine bracketed images, or stay open for an amount of time and “add up light”. The dimmer the light, the less we see, no matter how long we look at a scene. Both film and sensors can do this – and this ability to accumulate light impressions makes images in low light possible – at levels where nothing can be seen by the human eye.
• The eye is sensitive only to that part of the electromagnetic spectrum which is known as light. Photographic films and sensors can be sensitive to other types of radiation, e.g. infrared, ultraviolet, and x-rays.
• The focal length of the eye is fixed, and as such is limited. A camera cam be equipped with lenses of almost any focal length.
• The angle of view of the eyes is fixed, but lenses range in angle from a few degrees to 220°. The monocular AOV of an eye is (160° wide by 135° high), whereas binocular AOV is 200°×135° with an overlap of 120°.
• Human vision functions to see 3D things in a rectilinear perspective. Most lenses produce a perspective that is cylindrical or spherical.
• The focusing ability of the eye is severely limited with respect to close distances. Anything closer than about 25cm can usually only be seen indistinctly, with objects perceived less and less clearly the smaller they are, to the point where they become invisible to the naked eye. The camera, with the right accessories, has none of these restrictions.
• To the human eye, everything appears sharp at the same time (actually an illusion caused by the ability of the eye to autofocus). A camera can produce images with any degree of unsharpness, or images in which a predetermined zone is rendered sharp, while everything else is out-of-focus.
• The eye can adjust almost instantaneously to changes in illumination, by contracting and enlarging the iris as it views light and dark scenes respectively. The camera’s “iris”, its diaphragm, can only be adjusted for overall brightness. Therefore the contrast range of the human eye is much wider than that of a camera. On a sensor/film too much contrast would show up as an over-exposed (featureless, white) region, whereas too little contrast would show up as underexposed (dark) regions.
• The eye cannot express movement by instantaneously “freezing” an image of a moving subject, and cannot retain an image”. A camera can do both.
• The eye “corrects” for receding parallel lines in the vertical plane, e.g. tall buildings, yet considers those in the horizontal plane to be normal. The camera makes no such distinction.
• The eye sees everything it focuses on in the context of its surroundings, relating the part to the whole. A photograph nearly always shows the subject out of context, cut off from the surrounding visuals – a small limited view.