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

  1. #1

    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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    Black Pearl's Avatar
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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.

    Why is the image inverted in a pinhole camera?

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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.

  7. #7

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

    Question: what's the best way to reinvert this image if you're viewing it on the back of a translucency, keeping it in line of sight? (I.e no mirrors)
    What lenses, example distances... thanks

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

    TiMech You can't

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    James G's Avatar
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    Re: Why is the image inverted in a pinhole camera?

    Not sure why you would want to do this, but the only thing I can think of to achieve it would be to use a lens setup (design equivalent of an astronomical/marine telescope), focused on the backplate to re-invert.

    Very clumsy but possible?

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

    Here's an impractical idea (due to light loss), but couldn't you have a second pinhole and viewing screen to look at the image produced by the first?

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

    I started reading and thought Colin's back. Then I read the date on the thread!

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

    This is what Porro prisms that are used in binoculars are all about.

    https://en.wikipedia.org/wiki/Porro_prism

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

    Because there is no way of seeing what is happening inside. I'm sure that many, many people are just holding the camera upside down and turning the picture over when it's printed. I'm certain, from experience, that many of my own attempts with pinhole photography have gone sideways.

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

    A couple of years ago I had eye surgery to repair a macular hole. This involves draining the eye and refilling it with a gas that is gradually absorbed.

    Part way through, you have an eye with liquid at the bottom and gas floating on top. Except of courses the gas appears to be at the bottom, because our eye lenses work just the same as all the others.

    A neat demonstration, but not one I can really recommend.

    Dave

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

    A neat demonstration, but not one I can really recommend.
    Dave that's weird and somewhat disturbing....

    What does interest me though, is that you perceived the change in orientation and your brain did not 'normalise'. How long did it take to get back to normal vision?

    Just interested in a somewhat ghoulish fashion
    Last edited by James G; 10th March 2017 at 03:44 PM.

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

    Many years ago when I was a schoolboy (in fact many, many years ago), we were shown a series of films by the Moody Scientific Institute (Chicago?). One of the films described an experiment in which an individual was fitted with a head mounted binocular that turned the world upside down. After a period of wearing it, the individual started to see the right way up again because his brain compensated. The problems really started however. when he removed the head gear and of course found his sight inverted once more. Without conscious presence of the something justifying the effect, his brain couldn't cope and he went through a period of severe mental disturbance. Not one to try at home I guess.

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    davidedric's Avatar
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    Re: Why is the image inverted in a pinhole camera?

    I don't think I explained it very well.

    Things looked their normal way up. The gas bubble was at the physical top of my eyeball and therefore aligned with the bottom of what I was looking at, so it appeared at the bottom of my vision

    If you really want to experience queasy, the operation is performed under local anesthetic, so you can see what is happening

    Quote Originally Posted by James G View Post
    Dave that's weird and somewhat disturbing....

    What does interest me though, is that you perceived the change in orientation and your brain did not 'normalise'. How long did it take to get back to normal vision?

    Just interested in a somewhat ghoulish fashion

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

    So the pin hole image is upside down in the Northern Hemisphere! Hmm, I thought it was because I lived in Australia for my first twenty seven years.

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

    Quote Originally Posted by miatab View Post
    So the pin hole image is upside down in the Northern Hemisphere! Hmm, I thought it was because I lived in Australia for my first twenty seven years.
    Yes, and your circular polarizers spin the light in the opposite direction.

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

    Only if you put them in the sink and pull the plug.

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