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Why do our eyes see upside-down?

Why do our eyes see upside-down? (I know that your brain corrects it)
Leonard from Cambridgeshire (Aged 5-14)


2 Responses

  1. Dear Leonard

    Our eyes see ‘upside-down’ because of the way light is processed by the eye. Each human eye is a ball-like structure, with a small transparent opening at the front (known as the pupil) and a light sensitive layer of tissue at the back (known as the retina). In the mirror, you can see your pupil as a central black circle surrounded by a ring giving your eyes their distinctive colour.

    A simplified (but square) version of the eye can be made with a cardboard box that has a small pinhole in the centre of one side. This is a device known as a pinhole camera. The pinhole represents the pupil, allowing light to enter into the box, and the inside surface of the opposite side represents the retina. By aligning the pinhole camera with an object, and peering into the box through an opening in the box (being careful not to let too much stray light into the box!), it is possible see what is happening to light within the eye. An image can be seen on the inside surface that represents the retina.

    Light travels in straight lines and cannot pass through cardboard. Therefore, for a very small pinhole, light from one position on the object can only reach the back of the box at a single position (where light travels through the pinhole and continues on to the back of the box in a straight line). The same applies to each and every other point on the object. This effect builds up an image on the inner surface which is identical to the object. However the spatial relationship of points are reversed due to the straight path that light take passing through the pinhole. So objects appear upside-down.

  2. what makes our eyes see upside down

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