Cameras

You mean a "program" camera? There are three forms of automatic exposure: aperture-priority (usually marked "Av" - aperture value - on the camera's control knob), shutter priority (usually marked "Tv" - time value) and program. When you use aperture priority you set the f/stop and the camera picks the shutter speed to give the proper exposure. In shutter priority you pick the shutter speed and the camera picks the f/stop. In program mode the camera picks both.

The disadvantage of program exposure is it takes control of the image out of the hands of the photographer.

The advantage - and there is a huge one - is it lets the photographer worry about composing the picture without worrying about setting the camera. I know newspaper photographers. When they go to a fire or a crime scene, they hang the fastest lens they have on their cameras, set them to "high speed program" and go shoot. This gets them the most usable images and leaves them free to worry about more important things, like not getting run over by a fire engine.

The eyes as we know is that part of the body which helps us see. The phenomenon of the working of the eye is very similar to that of a camera. The human visual is system (HVS) is as complicated as the working of a camera.

Whatever we see, is the result of the message sent through the eyes to the brain. The brain interprets the signals sent from eyes to it hence allowing us to see what is in front of us. To understand a camera, human eyes should be understood first. It would be really fascinating to know the similarities and dissimilarities of both the processes.

Both the human eye and a camera use something called a lens. In fact, they both use the same type of lens - a converging lens or also known as a convex lens. Converging lenses are like the ones in magnifying glasses.

In the camera, the lens focuses the light onto a piece of film. The film has chemicals in it that basically trap the image on it, making it permanent. Instead of film, your eye uses something called a 'retina.' The retina has lots of little tiny things called 'rods' and 'cones' all over it. These are basically tiny antennae that tell your brain about the light that hits them. The rods tell your brain if there's light in a certain spot or not (a bit like a black and white photo) and the cones tell your brain what color the light is.

There is one spot on the retina, though, that has no antennae at all. This is the spot where the nerve leaves your eye to go to your brain. At this spot, you can't see anything at all - it's called your 'blind spot.' This is one of the reasons that you have two eyes; what you can't see with one eye you can see with the other. Unlike your eyes, cameras have no blind spot, so they only need to have one lens.

The individual components of the eye work in a manner similar to a camera. Each part plays a vital role in providing clear vision. So think of the eye as a camera with the cornea, behaving much like a lens cover. As the eye's main focusing element, the cornea takes widely diverging rays of light and bends them through the pupil, the dark, round opening in the center of the colored iris.

The iris and pupil act like the aperture of a camera.

The very back of the eye is lined with a layer called the retina which acts very much like the film of the camera.

Our eyes, very quickly adapt to the bright light, but in comparison, take a longer time to get adjusted to a dark environment. This is the reason we can't see anything when we enter a dark-room while when we move out of it, it takes very less time to adjust to the bright sun-shine. Though our irises may hurt a little in this process of adaptation to the bright light. But in case of a camera, a photographer has to do the task. The fuzziness of the view has to be removed by adjusting and modifying the light. This is automatically done by retina in case of human eye.

An interesting thing that I learned about pupils is that your pupil will also change size depending on what sort of mood you're in. But you sure can't tell the mood of a camera just by looking at it! Is it happy or is it sad? Hard to say.

SHUTTER SPEED

Vision is a continuous process of the human eye. But eye-lids act as shutters which creates a small time gap between two continuous visions. This small time gap is the shutter speed which is adjustable in case of camera but natural in case of human eye. According to researchers, an eye on an average has a shutter speed of around 1/50 of a second. Whereas, shutter-speed of a camera can vary from as less as 1/4000 of a second to as high as 2 seconds. Some cameras may even have an exposure time (shutter speed) of a few hours according to the need of the photographer.

APERTURE

Aperture of the eye or the lens decides the depth of field that is the area which remains in focus. The size of the hole of the aperture allows the required amount of light entering in the eye or the camera which results the focusing of a particular object of the whole view. The aperture of our eye is the black spot in the centre of the eye. It can vary from 1mm in the brightest light to 9mm at the night time. This is why this black spot shrinks when we move out in bright sun-shine and expands when we enter a dark-room.

Cameras and Eyes

The structure and operation of the eye is very similar to an electronic camera, and it is natural to discuss them together. Both are based on two major components: a lens assembly, and an imaging sensor. The lens assembly captures a portion of the light emanating from an object, and focuses it onto the imaging sensor. The imaging sensor then transforms the pattern of light into a video signal, either electronic or neural.

The camera and the eye have much more in common than just conceptual philosophy--the eye captures images as does the camera. The anatomy of the camera is more similar to that of a biological eyeball than many would imagine. Similar functions in common give the camera the appearance of a robotic eye. However, though there are many similarities between the two, they are by no means identical.

Cornea and Lens

The cornea is the "cap" of the eye; it is transparent (like clear jelly) and sits to the front of the eye and has a spherical curvature. The lens of a camera is also transparent (glass) and sits at the front of the body. Like the cornea, the lens also maintains a spherical curvature. The purpose of the corneal and lens curvature is to allow for the eye and camera to view, though not in focus, a limited area to both the right and the left. That is, without the curve, the eye and camera would see only what is directly in front of it.

Iris and Aperture

The aperture is to the camera as the iris is to the eye. The aperture size refers to how much light is let into the camera to be reflected on the sensor or film. As with the human eye, when the iris contracts itself, the pupil becomes smaller and the eye takes in less light. When the iris widens in darker situations, the pupil becomes larger, so it can take in more light. The same effect happens with the aperture; larger (lower) aperture values let in more light than a small (higher) aperture value. The lens opening is the pupil; the smaller the opening, the less light let in.

Focus

Both the eye and camera have the ability to focus on one single object and blur the rest, whether in the foreground (shallow depth of field) or off at a distance. Likewise, the eye can focus on a larger image, just as a camera (greater depth of field) can focus and capture a large scape.

Scope

As the eye, the camera has a limited scope to take in what is around it. The curvature of the eye and the lens allow for both to take in what is not directly in front of it. However, the amount of scope that the eye can take in is fixed, while a camera's scope can be changed by the focal length of different types of lenses.

Retina and Film

The retina sits at the back of the eye and collects the light reflected from the surrounding environment to form the image. The same task in the camera is performed either by film or sensors in digital cameras.