How do eyes work?

[Maxxxx]

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I usually see diagrams of eyes like this one, where the lens focuses the light on to the retina.

So how does this work with the lens equation 1/f = 1/o +1/i ?
Is the distance between lens and retina i or f? I think it should be i, and f is somewhere closer to the lens. Am I right?

 

[brood910]

For eyes, you usually assume that object = infinity. That's why most questions say that distance between retina and lens = focal length = i.

 

[chenzt]

.

 

[Maxxxx]

For eyes, you usually assume that object = infinity. That's why most questions say that distance between retina and lens = focal length = i.

I see. So if o is closer, f moves closer to the lens?

 

[milski]

I see. So if o is closer, f moves closer to the lens?

Unlike virtually all human made optical contraptions which focus the image by changing i (moving the lens back and forth), human eyes focus on closer objects by changing f, the focal length of the lens, by deforming the lens itself. And yes, when 0 decreases, 1/o increases, 1/0+1/i increases, 1/f has to increase, which means f decreases when focusing on closer objects.