Vision is the act or power of seeing.The eye
is the human organ which controls sight. In order to understand
the working of the eye, it is helpful to compare the eye to a
camera. The iris of the eye may be compared to the shutter of
the camera. As both control the amount of light entering
the system. The lens of the eye and the lens of the camera focus
the light to produce a clear image. The film of the camera is
comparable to the retina of the eye upon which the image is recorded.
In both the camera and the eye the focused image is recorded upside
down and backward. During the development process, the image is
turned the right way so we see the photograph as it is intended.
In the case of human sight it is a brain function that learns
to interpret the upside-down image in its proper position. The
eye though, unlike a camera, produces an ongoing view of the world
instead of one still photograph. Even still, camera is a good
analogy for how the eye functions.
The eye is a round organ encased in the skull. It is moved by six different muscles attached around the eyeball. After the light enters the pupil it is focused with the lens which then forms an image on the retina. A nerve impulse pattern is then formed by the rods (for black and white) and cones (for color) which make up the substance of the retina (there are millions of each of these). The optic nerve then conducts the impulses to the brain. Within the brain a mental image is formed. The eye basically receives light reflected by objects from the surroundings and encodes it into message form so that the brain can read it.
Holland Thompson once asked, "Why can we not see the bottom of a river?" The answer is that light travels in a wave length that bends and is reflected. When light passes from air into water part of it is reflected. The portion of the light that is reflected backwards from the surface of the water is that portion of light not revealing what is beneath the surface of the water. If all of the light is reflected from the surface of the water into the eye, nothing beneath the surface of the water will be visualized. It is the light which enters the eye that produces vision. The amount of light reflected from the surface of the water depends upon the angle subtended between the eye and the surface of the water, the angle between the light source and the surface of the water, and the refractive index of the water. The more light that is reflected from the surface of the water into your eye the less you can see within the water. The more light that penetrates the water, strikes an object and returns to the eye the better we can see objects within the water.
When viewing things underwater they seem out of focus unless one wears a diving mask. In our experiment we focus on the idea that things appear larger under water. The reason for this, is that water reflects and bends light differently than air does. Wearing a mask under water helps us focus because it restores the natural amount of air to the space surrounding the eyes. The mask lens, allows a bubble of air to be in front of the eye. One set back to the mask is that there is a magnification, caused by the glass lens of the diving mask, causing objects to appear larger and closer. The objects in the water appear closer because light bends.The diving mask is essential for a diver who wishes to perceive any detail in the objects visualized underwater. Without the diving mask objects can still be visualized, however they appear "blurry" to the observer.
Vision underwater would be quite limited without the use of diving equipment such as diving masks, goggles, and external light sources such as flares or electrically powered lights. With the proper combination of equipment, the diver can expect to have clear vision with photographic detail at almost any depth, day or night. Without any assistive equipment underwater vision suffers considerably, therefore taking away from what observed clearly.