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I learned that a pinhole camera inverts the image on the film strip:

enter image description here

Is it to possible to test if the image gets inverted without the film strip on which the image is projected?

For example: I made a small hole in the cardboard and tried looking through it, but the image didn't appear inverted to my eye. Why?

Is there a simple experiment I can use to prove that the image gets inverted without using a filmstrip?

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    You are not suposed to look through the hole. – Rafael Aug 23 '16 at 16:07
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Replace the back wall of the camera with a sheet of tracing paper, ground glass (or similar translucent material) and observe the resolved image from behind the camera. You may need a dark sheet over your head (and the rear of the camera) to allow the dim image to be visible. This should remind you of how very old cameras were operated (for exactly the same reason).

It may also be worth looking up camera obscura to see more examples (at different scales) of the principal in action.

Pin-hole cameras, camera obscuras, cameras and the human eye all resolve an upside down image - which is then rotated for viewing (or when being interpreted by the brain).

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    Nice explanation, exactly what I came here to say. A newtonian reflecting telescope also gives quite an interesting inverted image if you know anyone who has one of those (a lot of mid size back yard telescopes are newtonian designs) – Joseph Rogers Aug 23 '16 at 20:55
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Make a simple, non-photographic pin-hole camera. Start with a cardboard tube. The round Quaker Oats breakfast box is perfect for this job. You can use any cardboard mailing tube. Cut off both ends, now you have a just the tube. Cover one end with a single sheet of tracing paper. In my day, we called this paper “onion skin”. Cover the other end with aluminum foil. Use duct tape to affix the foil and the tracing paper. Using an sewing needle, pierce a tiny hole in center of the aluminum foil.

Now darken the room as best you can. Allow your newly constructed camera obscura to look out a window. You will see an upside down image of the outside world projected on the tracing paper.

The camera obscura, as it was called, was popular in Europe before the camera. Artist made and purchased elaborate camera obscura devices. These were often placed inside a tent. The idea was to use the projected image as an aid, they traced the image and later, finished it using water colors or oils.

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  • Waxed paper also works in lieu of 'onion skin' paper. – Michael C Feb 2 '18 at 23:54
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How did you look through the pinhole?

If you put it far from your eye you have seen nothing. It is small hole and you have seen one "overexposed" point behind dark card.

If you put the card as close to the eye as possible think of it as another lens in your eye. And the image was already inverted - it was projected on your retina and your brain automatically re-inverted it so up was up and down was down.

There is no way how pinhole projection can not be inverted. There is no reason to make camera lenses that won't invert the image - the drawbacks of design are far more serious that dumping the chip in correct order, see basics of operation of CCD, (digital cameras), turning the film correctly when developping (film cameras) and adding pentamirror ([D]SLRs' viewfinder). Note that waist-level cameras have inverted viewfinder.

OK, there is one, but it is a Heath-Robinsonian solution: Build your camera with pinhole, translucent screen, another pinhole and the film/CMOS/CCD. This way you'll have inverted image on the screen and double-inverted image on the film.

If you want to see the pinhole effect, find a room, cover all windows except for one small hole. The room will be completely dark, except for the projection of the outside world on the wall opposite to the hole. You will be inside the camera obscura.

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    There's no need to have a matrix inversion calculation in the digital camera either. They can just mount the sensor 'upside down' in the first place. Similarly our retinas are 'upside down', so there's no need for our brains to invert the images. – bdsl Aug 23 '16 at 13:36
  • @bdsl I've heard somewhere that small children see upside-down until they learn that up is up. – Crowley Aug 23 '16 at 13:39
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    @Crowley there's no "upside down" in the brain, the concept does not make sense. There's no Cartesian homunculus behind your eyes observing the projected imagery like a movie on a silver screen. Photons are turned into electric signals and electricity cannot be "right side up" or "upside down". – JohannesD Aug 23 '16 at 16:04
  • @JohannesD there are receptors that tells the brain whether the head is facing up or down. Brain also "knows" whether the hand is moving up or down. Then it correlate this with the signal from eyes. The image projected on retina is upside down, but the direction is percieved according to the expirience. Regardless the "wiring" of the retina and brain. – Crowley Aug 23 '16 at 16:30

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