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In this first diagram the two grey rays $OXI$ and $OPI$ are the rays I used to find out where the top of the image is formed. They are called the construction ray and these are usually the only two rays that you see on a ray diagram. However in reality all rays bounded by rays $OWI$ and $OZI$ go through the lens to form the image. If I put an obstruction ...

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You are probably referring to the conventional representation of rays in geometrical optics, where typically two rays are drawn to define the image, which is exactly where they cross. You can also draw 20 of them but 2 is minimum. So this is just the property of the sharp image - all rays from the object are collected in a single point of the image. In any ...

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If the 2 objects are at different locations, then the green light is hitting different group of cones in your eye than the red light. You should thank to the lens in your eye which is sending the light rays to different areas on your retina, depending on the direction from which the light is coming. Without the lens, all light would hit all cones at the same ...

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What happens to photons when they hit our eye? Some of them pass through the iris and are focussed by the lens onto the retina where they are absorbed by rods or cones. where do they end up? Some of them end up absorbed by rods/cones, some by other tissues, some are reflected (c.f. red-eye in photography). why our eye don't get overheated? ...

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