Index

• Basic elements and materials
• Focal distance and angle of cover
• Shutter
• Diaphragm (or pinhole)
• Rapid guide for the construction of a camera

Basic elements and materials

The basic elements of a pinhole camera are the same as those of a conventional camera (except for the objective, that in our case is substituted by a small hole named pinhole).
We should know these elements well, since their measurements are interrelated: the geometry of the camera will determine the focal distance and the angle of cover, and these to their time, condition the diameter of the pinhole (that is to say, the diaphragm of our camera).

The camera is a tight recipient to the light, generally in form of prism, although it could also have another form in order to create diverse effects.

Any recipient that we recycle could serve in order to manufacture a camera. Also we could construct it with wood, thick carton, plastic.etc.The only condition is that the material that we utilize is totally opaque to the light.
The election of the material and the completion will depend on the durability that has been foreseen for our camera.

Focal distance and angle of cover

The focal distance is the distance is formed between the pinhole and the focal plan, where the image and the sensitive emulsion (the film) is placed. The angle of cover is the scene that is covered with the camera.
The relationship between these two elements is inversely proportional: a greater distance corresponds to a minor angle of cover and vice versa.
Knowing this angular, we could design a camera that covers the same scene as an angular objective, normal objective or a teleobjetive. According to the measurement of focal distance and the diagonal of the negative that we are going to utilize, we will get a type or another of camera.

The camera of normal focal distance is the most similar to the human vision, since its angle of cover (45 grades, approximately) resembles the angle of vision that the human eye covers with neatness, although we can detect movements astrance in bigger angles.

Shutter

It is the mechanism that regulates the time of exposition to the light of the negative, and that is are located covering the diaphragm (our pinhole).
According to the durability that has been foreseen for our camera, the Shutter could be:

1. A cover of an opaque material (wood, metal.etc.) with a simple mechanism of opening (hinges, shiding guides, etc.) in order to leave the pinhole uncovered.
2. A simple perforation of the face of the camera (previously clipped and covered with an aluminum sheet) in the moment of taking the photo.
   Once transcurred the time of exposition, the pinhole is covered with adhesive black ribbon.

Diaphragm (or pinhole)

The diaphragm is the hole through which the light enters to the interior of the camera. Its diameter regulates the quantity of light that arrives to the negative. In our case, the diaphragm is the pinhole and its size depends on the focal distance.
Their relationship is given by the following formula:

(d:pinhole diameter. F: focal distance)

It is important to make a pinhole (perforating the metallic sheet that covers the frontal of the camera) adequate to the focal distance, since:

• A pinhole too big will allow much light, but we will lose definition in the image.
• A pinhole too small will give good definition but the time of exposition (in order to make the take) will be excessive.

The pinhole could be made with a conventional needle pressuring on the metallic sheet, that could be of tin or of aluminium paper. The sewing needles are gauged according to the following scale:

The f number

Once we have constructed the camera, one must calculate the brightness of the pinhole in order to carry out the take correctly.
The f number corresponds to the diaphragm value, as in a conventional camera and indicates the inverse value of the proportion of light that the diaphragm retains in order to facilitate the formation of the image..
An ideal diaphragm would allow 100% of the external light, that is would have an f value equal to 1. An f value equal to 2 would mean that half of the light would pass... and successively. The calculation is carried out following this formula:

(F: focal distance. d: pinhole diameter. )

Later we must approach the value of the f number closer to the scale of f numbers, that is the following:

This approach is necessary in order to calculate the time of exposition correctly, and to carry out good pinhole takes.

Rapid guide for the construction of a camera

Let's suppose that we want to construct a simple camera starting from a box of carton whose measures are: 100 X 150 X 100 mm. (long X wide X high).

1. The first steep to follow is to reinforce the box in its weaker points (vertexes) and in the parts that will have more use (the posterior cover, where we will change the sensitive support, and the anterior, where we will place the metallic sheet on a hole cut in the box). Later we will paint the interior of the box in black to avoid internal reflections not desired.
2. We will continue with an analysis of the geometry of our camera. The focal distance will be 100 mm. (measurement of the lenght) and the diagonal of the sensitive support will be 180 mm., so that we will have a camera of angular type in our hands.
3. Next we will calculate the diameter of the Diaphragm (applying the formula), getting a value of 0.4 mm. We will use a needle of the number 11 in order to get a pinhole of that diameter.
4. The calculation of the f number will report us a value of 250. In this case we will look for a value of 256 that figures in the table off numbers.
5. Once covered the pinhole with adhesive black ribbon, we will go to the dark room to load the camera with the sensitive support (paper or movie). We will fix it to the posterior cover of the box.

   Now the camera is ready to carry out our first take.

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