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A simple
Photographic Camera

G. Carboni, August 2008
Translated by Sarah Pogue, June 2010

 


CONTENTS

Presentation
Pinhole camera
Camera with lens
Materials and tools
Construction
Testing the camera
Using the camera
Conclusion
Bibliography

Figure 1 – The completed photographic camera.


PRESENTATION
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This article describes how to construct a photographic camera for children. As with other articles in this gallery, instead of building only one instrument, we will build two, the first of which is very simple and which paves the way for the second. I have to say that most adults don’t consider these to be authentic cameras, but only a “camera obscura” (dark chamber) or viewer, but for children these will be not only photographic cameras, but even film cameras (adults obviously have psychological shortfallings!). Both of these will be constructed from shoeboxes and can even be realised in a primary school.


PINHOLE PHOTOGRAPHIC CAMERA
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Figure 2 – Pinhole camera. Figure 3 – Open pinhole camera. Figure 4 – Tools to build the
cameras described in this article.

We will begin with the pinhole photographic camera. As you can see in figure 2, to make this camera it is sufficient to make a small hole on one side of a shoebox and apply a translucent screen to the opposite side. Specialists call this hole a "stenopeic hole", but we, as ordinary folks, will call it a pinhole and it must have a diameter of approximately 2 millimetres. (Even the automatic spellcheck of the programme I used to write this text refuses to accept the term “stenopeic” and it underlines it in red).

On the opposite side from the hole, you must create a rectangular opening. It will not be easy for you to fix the piece of white plastic cut from a shopping bag to this window so, to facilitate the operation, make a cardboard frame as shown in the figures 2 and 3, and then fix the piece of plastic to this frame using a stapler. Now, you just have to put the frame in place and fix it with two more staples.

You won’t believe it, but the first camera is already finished. However, to use it successfully, some adjustments are necessary. In fact, the image produced by the light that passes through the pinhole is very faint and the ambient light that hits the screen is enough to make it invisible. You will have to procure a piece of black cloth, e.g. an apron, and wrap it around the posterior part of the camera. Furthermore, you will have to illuminate well the objects that you want to see. At this point, to see the image produced by your instrument, you must put your head under the cloth. The image that you see will still be very dark and also not very clear. To resolve these problems, we will move on to the second device.

CAMERA WITH LENS
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With a lens and a shoebox you can build a fun camera for children that can produce quite bright and clear images. This instrument can also be made in primary schools, and is suitable for conducting experiments on the formation of images and for introducing some fundamental concepts of optics.

Figure 5 – Sketch of the second camera.

Figure 6 – Length of the fixed part and
the mobile part of the second camera.

Figure 7 – How to measure the focal length
of a lens at the moment of purchase.


MATERIALS AND TOOLS

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- a magnifying lens with a focal length between 12 and 17 centimetres (between +6 and +8 dioptres) ;
- a shoebox;
- a piece of translucent plastic such as that used for plastic shopping bags;
- some cardboard (this can be taken from a second shoebox);
- a pair of strong scissors, Stanley knife, compasses, pencil, ruler, stapler;
- glue for cardboard and a brush.

Amongst the tools needed a pair of robust scissors such as those shown in figure 4 are very useful. Children’s scissors are often too weak to cut cardboard.

The principal component for constructing this camera is the lens. For this purpose a magnifying lens such as that shown in figures 4 and 7 is suitable. You can buy lenses of this type at very low cost at a market stall or you could try a photography shop. You can also find suitable lenses at low prices in stationery shops.

To verify if the lens is suitable for this experiment, you must determine at least approximately its focal length. In order to do this, you can focus the image of the sun on a screen and measure the distance from the image of the sun to the lens. If you are in a closed environment, instead of the sun you could focus the image of a lamp or of a window at least a couple of metres away (figure 7). To determine more precisely the focal length of a lens, refer to the article indicated in the bibliography.


CONSTRUCTION

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Before proposing this experiment to a primary school class, the teacher should construct the camera himself. In this way he will have the time necessary to examine any difficulties and to find a solution; furthermore, this first camera can serve as a model for the students. In figure 5, you can see that the front part must be fixed to the cover beneath by means of some staples. The back part instead must be mobile because it serves for focusing. With regard to figure 6, the mobile part is cut lengthways for a distance equal to that of the focal length (F) of the lens. This will allow you to focus on distant objects. The fixed part must be 2 cm shorter to consent the extraction of the mobile part. As you can see in figure 8, from the cutting of the box to obtain the fixed part and the mobile part, an intermediate part can remain which can be thrown away or used for other purposes.

 

Figure 8 – Cutting the shoebox (the cover is not cut).

Figure 9 – The mobile part must be lowered.

Figure 10 – Fixing the screen.

 

In order to focus, the back (mobile) part of the box must be able to fit into the front (fixed) part. Therefore, you should lower the back part by approximately 5 mm (figure 9).
In the back part, open a window. With a piece of cardboard and a piece of translucent plastic make a screen like the one that you made for the pinhole camera and fix it to the end (figure 10).

 

Figure 11 – Make a hole for the objective.

Figure 12 - With cardboard, glue and
a stapler, fix the objective in place.

Figure 13 – Fix the front part to the cover.

 

On the front face of the box, make a hole with a diameter a little smaller than that of the lens (figure 11). With two sheets of pierced cardboard, glue and a stapler, fix the lens to the box (figure 12). The hole in the middle sheet of cardboard should be equal to the diameter of the lens. The diameter of the hole in the second piece of cardboard should be a little smaller than that of the lens, like the one in the box. In the end, the lens will be held firm between three layers of cardboard: the one of the box and the two layers of added cardboard. The middle sheet of cardboard keeps the lens centred, while the other two layers keep it steady like in a sandwich. The glue and staples will keep the lens in its place. With the stapler, fix the front part to the cover (figure 13).


TESTING THE CAMERA

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Go into a room and turn off the lights. Pointing the camera towards the window, you should see a part of the view outside. Moving the mobile part forwards and backwards, focus the camera. Shorten the mobile part if it hits off the fixed part before the image of distant objects is in focus. Now the camera should work correctly.

 

Figure 14 – Camera with diaphragm.

Figure 15 – Testing the
camera with diaphragm.

Figure 16 – Testing the
camera without diaphragm.

 

Turn off the light in the room and, with a table lamp, illuminate well some coloured objects (figures 15 and 16). Looking at the screen, try to centre the objects, then focus the image by moving the mobile part. Most probably, you will have obtained a very luminous image of the objects but one which is not however very clear.

From an opaque piece of cardboard, cut a rectangle approximately 10 x 14 cm in size. In this piece of cardboard, make a hole about 2 cm in diameter in such a way that it is at the same height as the centre of the lens. Observing the same objects with the camera equipped with this diaphragm, you should see that their images are now less bright but clearer. Therefore, if you want to see the objects more clearly, insert the diaphragm, and if you want to see them more brightly, remove it. While you focus the images, you will realise that the closer an object is, the greater the distance between the screen and the objective must be. To know why, read the article indicated in the bibliography.


USING THE CAMERA

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The camera is ready and you can have fun using it to observe the images that form on the rear screen. If you want to observe objects in the open air, it is a good idea to cover the back part of the camera with a black apron, under which you must put your head. For this purpose the leg of an old pair of black trousers can also be used, which, if necessary, you can widen by cutting it in order to breathe better.

Using this instrument, you will realise that the objects appear upside-down. This is explained by the fact that light travels in a direct line. Therefore, passing through the lens, that which was on top ends up on the bottom and that which was on the right ends up on the left. This phenomenon also happens with normal photographic cameras and even in your eyes. Note also that this camera also works in colour and it can even be used as a film camera.

In a class, you can carry out this experiment in two ways. You could allow each child to build a camera of his own. 4 lessons of 2 hours each and a reasonable amount of confusion will be necessary to achieve this. Otherwise, you could make only one, showing the children how it is done. Then, you can give it to one group of children at a time as a model to make one together at home. Many children will not even need the model. It is important for the teacher to put the children into groups so that they can work together when building their own cameras. In middle school, it is possible to conduct these experiments together with others regarding optics that you will find in the article indicated in the bibliography.

Whoever wants to take some further steps can, in fact, substitute the transparent screen with photographic film transforming this instrument into an authentic camera. Using very closed diaphragms you can use your hand or a bottle top as a shutter. Applying a Polaroid back, you can obtain photos in a few seconds and with the pinhole system you can demonstrate how to take photos even without an objective (a little bit of magic).


CONCLUSION

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With these simple experiments, the children will have learned different things on the functioning of real photographic cameras. It remains for the teacher to explain the analogy between the screen and the film, the characteristics of the diaphragm, what the shutter is and how it works and some elements of perspective.

If you use your bedroom as a darkroom, you will transform it into a marvellous place where you will find yourself immersed in the panorama that stretches out outside your window, as indicated in the article: "The sky in a room".


BIBLIOGRAPHY
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From the lenses to optical instruments Introductory article on optics.

 


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