The Human Eye is our own camera. It has components and qualities similar to that of an Single Lens Reflex (SLR). It has a variable focus lens, aperture and sensors. We can now explore the properties of the Human Eye.
One basic property of cameras are focusing distance. Most lenses' specifications include their minimum and maximum focusing distance. This is where the lens can be adjusted to focus on a certain distance of the object. Similarly, the lens of the eye varies by contracting and retracting of the muscles around the lens. But, ofcourse, there is a minimum distance at which the muscle can compensate to focus on the object.
So, for this part, we explore the differences of minimum focusing distance of each eye and when using both eyes at the same time. To measure the effective minimum focusing distance of both of the eyes, a pen, with its tip, was placed squarely in front of both eyes and was then brought closer to the bridge of the nose until it can no longer be seen focused. The distance between the pen's tip to the bridge of the nose was then measured and recorded. For measuring the minimum focusing of each eye, same procedure was used except that one eye was covered. The result of the experiment is tabulated below.
Table 1. Minimum Focusing Distance of two subjects
As we can see from table 1, that each eye of both individuals have different minimum focusing distances, and when the distance was measured for both eyes, the obtained result has a value lesser than the value recorded for each eyes. This was not expected, it was expected that the minimum focusing distance of both of the eyes should have a value averaged of that the minimum focusing distance of each eye. However, the values obtained for both eyes on each subject is still acceptable, since many factors affects the focusing of both eyes, such factors are vision defects like astigmatism, nearsightedness, and farsightedness.
Let's now explore the peripheral vision of the eye. Peripheral vision, according to Wikipedia, is a part vision that occurs outside the center of gaze. In humans, peripheral vision is weaker compare to other species because the human eye has a greater concentration of receptors at the center and less at the edges. Because of this, human eyes can greater distinguish color and shape at the fovea (the region on the retina where the concentration of receptors are greater) than any other region of the retina.
To measure the maximum peripheral vision, both of the eyes are fixated to a point on the wall at a distance of 1 meter. A vertical pen was again placed squarely in front of both of the eyes and touching the wall. The pen was moved from the center to the left travelling along the wall until it can no longer be seen. The distance was then measured from the center to final position of the pen. The same procedure was repeated but the pen was moved now to the right. The data obtained is tabulated below.
Table 2. Maximum Angle of Peripheral Vision of two subjects.
According to WikiPedia, normal vision extends to around 100 degrees away from the nose or outward. We can see in Table 2 that our experimental data coincides with rough approximations.
Our next stop in human eye exploration is the visual acuity. Visual acuity is the acuteness or clearness of vision. It is a measure of the spatial resolution of the visual system, or in this case, the human eye. The common test used in measuring visual acuity is the Snellen chart.
Figure 1. Snellen chart used in measuring visual acuity. Image is taken from Wikipedia (http://en.wikipedia.org/wiki/File:Snellen_chart.svg).
For this part, visual acuity was not measured via Snellen chart, it was measured by looking how far can the eye clearly discern the letters in a line (or in a sentence) at a distance. The eye was fixated at one letter and all other letters in the line was covered. One by one, the letters was then uncovered until it can no longer be distinguishable. The distance was then recorded and the angle was computed by using basic trigonometry. The tabulated results are shown below.
Table 3. Visual Acuity of two subjects.
From table 3, both of the subjects have maximum angle of visual acuity close to 5 degrees. In search of theoretical values of normal human eye visual acuity is still in progress to validate the the significance of the obtained data.
Finally, we can explore the scotopic and photopic property of human vision. Wikipedia defines scotopic vision as the vision of the eye under low light conditions and photopic vision under well-lit conditions. Under low light conditions, cone cells are non-functional. This is why we have difficulty seeing color in dark places. Our vision is therefore governed by the rod cells which are sensitive to 498 nm (green-blue). This is comparable to the rods sensitivity which is around green wavelength (555 nm).
To characterize our eyes to its sensitivity, we fashion a box. On the inside of one end of the box, we place strips of colored paper. On the other, we create a viewing slit. A garbage bag is placed at the slit so that the viewer can bury his face in the garbage bag while viewing the colored strips without allowing external light to enter. A small hole was then placed on top to allow light from a flashlight to pass. The light source was then lowered and raised to increase the intensity of light entering the box. A run was conducted with the light being slowly lowered to increase the intensity of light. And a second run was conducted with the light being raised slowly to decrease the intensity of light.
Table 4. Scotopic and Photopic Vision
In the table 4 first run, we can see that yellow is the first color that can be distinguished by both subjects. This is to be expected since yellow and green are very close to each other in terms of wavelengths. We can see a slight discrepancy in the next few colors noticed. This can be due to the fact the appearance of color is quick thus can confuse the viewer. In the second run, it much more coherent. We can see that violet is the first to disappear. This is expected since violet is farthest from the green wavelengths.
Another property we can explore is the blind spot. Inside a human eye is a distribution of rods and cones which are the reason we can see. But in a certain area, the nerves from the sensors are bundled together and enter the body to the brain. In this area, there are no rods and cones. So when looking at a certain object with one eye, there is a small area which we cannot see.
A few test we can do to examine the existence of the blind spot is the basic x and o test. We look at an image of an "x" on the left side and a "o" on the right. If we look at "o" and move the image, there is a certain distance that the "x" will disappear. This same test can be done with a GIF image. We can create a GIF image with a stationary "x" on the right and a moving "o" on the other. If we stare at the "x" with one eye, we will notice that the "o" will appear and reappear as the "o" moves.
To compensate for this, our brain adjusts by using patterns around the blindspot. To understand this better, we can look at an image of straight vertical lines with a white circle in the middle. If we stare to one side and move the image around, we can find the spot where the white circle is in the blind spot. This can be seen when the image appears to be purely straight vertical lines. Our brain compensates the blind spot by filling in the gap.
From these experiments, we can see that the human vision has numerous properties that affect how we can see. Though color is a very subjective topic, we can see that the human eyes react to color in a very scientific way.
