In the studies on Optics, we have seen several concepts, such as the principle of straight light propagation, mirrors, image formation in a mirror, lenses in general, etc. But in Optics, a subject that arouses a lot of interest is the study related to vision. Thanks to vision, we can see objects around us, people, cars, etc. Therefore, we can say that the main purpose of studying Optics is the understanding of human vision.
See the picture above: in it there is a boat far away. Suppose you are on a beach watching the boat in the figure above. In that case, you won't hesitate to say the ship is far away. So when you can make this statement, "the ship is too far away", you can say that it is in infinity. it is said infinite because the distance that separates you from the ship is much greater compared to the dimensions of the elements of your eyes.
In this case, when you look at the ship, you can see it because the light rays coming out of the boat reach your eyes. Because they are so far away, these light rays arrive practically parallel to them. Don't forget that the image focus is located on the retina. So, see the illustration below, where there is a representation of an object placed 25 cm away from an eye. Then observe the behavior of light rays that depart from the object towards the eye.
In this illustration we can also say that the object is at infinity. Therefore, our eyes do not have the muscle strength to see the object, so we have a feeling of rest in our eyes. The farthest point from our eyes and which still allows us to see any object we call remote point. Therefore, in light of this, we can say that the remote point of the human eye in general is at infinity.
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Now think about the following situation: at each interval of time the boat approaches the beach. Therefore, we can say that he is approaching you who are at the edge of the beach. Depending on the ship's approach, you will continue to see it perfectly; or, if you get too close, you will find it somewhat difficult to see it. Therefore, the minimum distance an object can be to be seen clearly, without getting out of focus, is 25 cm, for a normal adult human eye. This minimum distance at which an object is clearly seen is called the near point. See the illustration below:
By carrying out a simple experiment you can try to locate your nearest point. So let's see: get a pen or a pencil. Now hold it a certain distance from just one of your eyes. Look directly and constantly at the tip of the pencil. Then, slowly, bring it closer to your face, checking what is the shortest distance from your eye that still allows you to see it clearly. With this experience you can see that distances shorter than this give blurry, unclear images.
In order to always try to keep the image of an object very close to our eyes sharp, we can feel great muscular effort in the region. We can see this tiredness when we take long readings. Therefore, after long readings it is recommended to fix the vision at a remote point, that is, a point farther away from the eyes to provide them with rest.
By Domitiano Marques
Graduated in Physics
Would you like to reference this text in a school or academic work? Look:
SILVA, Domitiano Correa Marques da. "Visual accommodation"; Brazil School. Available in: https://brasilescola.uol.com.br/fisica/acomodacao-visual.htm. Accessed on July 27, 2021.
