What is the Relationship Between Focal Length and Distance in the Human Eye?

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In summary, Joe is hiking through the woods when he takes a break to admire the view. He remembers his physics class and thinks about how the human eye works. He focuses on a tree and the focal length of the cornea-lens system in his eye must be less than the distance between the front and back of his eye. The focal length can be adjusted by changing the curvature of the lens, which is closer to the fovea at the back of the eye.
  • #1
Badger
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Homework Statement


Joe is hiking through the woods when he decides to stop and take in the view. He is particularly interested in three objects: a squirrel sitting on a rock next to him, a tree a few meters away, and a distant mountain. As Joe is taking in the view, he thinks back to what he learned in his physics class about how the human eye works.

Joe first focuses his attention (and his eyes) on the tree. The focal length of the cornea-lens system in his eye must be __________ the distance between the front and back of his eye.
A - Greater Than
B - Less Than
C - Equal To


Homework Equations


None

The Attempt at a Solution


I don't know where to begin. I believe focal length on one side of a lens is the same as the focal length on the other side. But this problem talks about this cornea-lens system, a "compound lens system," which throws me off.

But here's my flow of logic, please feel free to comment.
-Our eyes are converging lenses
-Our eyes can change the focal length in order for us to focus on objects at different distances.
-The object is a real inverted image after it passes through our eye
-The image must focus on our fovea in order for it not to be a "sharp image"
-The fovea is at the back of the eye.

So if the fovea is at the back of our eye, which is where the image needs to be focused, that means the focal length is B) equal to that distance?
 
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  • #2
Your eyes can change squeeze their lenses around their perimeters, changing their curvature and thus their focal length. Does this help?
 
  • #3
Not so much turbo,

I don't know much about the eye and after studying a handful of diagrams, I still don't know.

Can we change the curvature of our eye so the focal lengths ("outside" and "inside" the eye) are not equal? Is it possible? All my readings and notes show converging lenses where there is only one focal length, never two different ones. Is it safe to assume that's how it for the lenses in an eye? The focal length can be adjusted but its always equal to?

R,
The Badger
 
  • #4
The answer is less then, the focal length could be any distance as long as it's not greater than the space within the eye.

Sorry I cannot provide a proper explanation
 
  • #5
The "focal length" is the distance at which PARALLEL RAYS FROM INFINITY would converge. When looking at the tree, are you focusing parallel rays from infinity?
 
  • #6
The distance between the front and back(fovea) of the eye remains constant. Focusing is done by adjusting the curvature of the lens which is nearer to the fovea that the front of the eye.
 

1. How does the human eye focus on objects?

The human eye focuses on objects through a process called accommodation. The muscles in the eye change the shape of the lens to focus light rays onto the retina, allowing us to see objects clearly.

2. Can the human eye focus on objects of different distances?

Yes, the human eye can focus on objects of different distances through the process of accommodation. The muscles in the eye adjust the shape of the lens to focus on objects at different distances.

3. Can the human eye focus on multiple objects at the same time?

No, the human eye cannot focus on multiple objects at the same time. The eye can shift its focus quickly between different objects, but it can only focus on one object at a time.

4. How does age affect the focusing ability of the human eye?

As we age, the muscles in our eyes become less flexible, making it more difficult to focus on objects up close. This is known as presbyopia and is a natural part of the aging process. However, corrective lenses can help improve near vision for those with presbyopia.

5. Are there any exercises to improve eye focusing ability?

While there are no proven exercises to improve eye focusing ability, maintaining a healthy diet and regular eye exams can help keep the muscles in the eye strong and maintain good vision. It is also important to take breaks from screens and focus on objects at different distances throughout the day to prevent eye strain.

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