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Thread: Why is the image inverted in a pinhole camera?

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    Why is the image inverted in a pinhole camera?

    Im in yr11 of secondary school (uk) and i do seperate science GCSE. For homework we were asked to find out why the image is inverted in a pinhole camera, any help would be much appreciated!
    Last edited by Colin Southern; 30th September 2011 at 03:54 AM.

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    Re: Why is the image inverted in a pinhole camera?

    Essentially, because the aperture (hole) is so small, it bends the light in a manner that inverts the image. It is not just upside down, but it is also a reversed image. If you can imagine a beam of light hitting the aperture opening as coming in from the shape of a equalateral triangle, when it enters the lens (aperture opening) the beam is reversed and an equal sized angle of light is projected on the film plane. The size of the image is determined by the focal length of the aperture, but generally for an aperture size of .256, you will have a focal length of about 3 inches (77mm).

    Or...for a far more mathematical explanation,

    http://en.wikipedia.org/wiki/Pinhole_camera_model

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    Re: Why is the image inverted in a pinhole camera?

    First off the image is upside down and back to front in all cameras.

    A pinhole does not bend light, you need a black hole to do that and they are a bit of a different proposition all together. The reason is very simple.

    Light does not usually bend but travels in a straight line so the light from the top of a scene passes through the pinhole, continues in a straight line, and ends up at the bottom.

    Dizzy found this helpful.

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    Re: Why is the image inverted in a pinhole camera?

    Quote Originally Posted by black pearl View Post
    Light does not usually bend but travels in a straight line so the light from the top of a scene passes through the pinhole, continues in a straight line, and ends up at the bottom.
    @ Sharmaine - just think of a ray light being like a jet of water from a garden hose being aimed at a hole in the fence; Shoot from the right, it ends up on the left. Shoot from the top, it ends up on the bottom.

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    Re: Why is the image inverted in a pinhole camera?

    If a digital camera, or a film camera for that matter - if you could look at the film before it was developed, displayed the image exactly as it 'sees' it from the lens, it would be upside down and backwards. That is the way the image is always projected onto the film plane as shown in Black Pear's diagram.

    If you used a old fashioned camera where you got under a cloth cover to focus and put in the film, the image you would see on the glass back of the camera would be upside down and backwards. Seeing the image right-way around is a relatively new feature.

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    Re: Why is the image inverted in a pinhole camera?

    Quote Originally Posted by Boatman View Post
    If a digital camera, or a film camera for that matter - if you could look at the film before it was developed, displayed the image exactly as it 'sees' it from the lens, it would be upside down and backwards. That is the way the image is always projected onto the film plane as shown in Black Pear's diagram.

    If you used a old fashioned camera where you got under a cloth cover to focus and put in the film, the image you would see on the glass back of the camera would be upside down and backwards. Seeing the image right-way around is a relatively new feature.
    You're right Homer. The right-way round viewing is achieved by the pentaprism. It's a bit difficult to describe, but if you look at the reflective surfaces of one you can see how it 'swaps' the image round in the viewfinder.

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