- Control the amount of light passing through the lens
- Control the amount of time the film is exposed by light
The Diaphragm / Aperture
The size of the lens opening, also knows as the aperture, let's you change the amount of light going through the lens. A part called the iris diaphragm makes this happen. It consists of a series of overlapping metal plates that move at a certain speed. Just like the iris in your eyes, it controls the diameter where the light is captured.
The Shutter Speed
The amount of time the film is being exposed by light is determined by the shutter speed of the camera. The most common technique is called a focal plane shutter.
You can compare it with the curtains by a window. Before you take a picture, the light is being blocked by the "curtains". This makes sure the film is not yet exposed to any light. Then, when you take the picture the "curtains" open and for a certain amount of time light reaches the film.
To achieve this effect, the camera is filled with gears, switches and springs. When you take a picture, a lever is released and several gears are set in motion. Different shutter speeds are possible by adjusting this mechanism.
ISO value
But before you can take the shot, you need to know the right aperture and shutter speed. The ideal settings also depends on the size of the light-sensitive grains in the film. Each film has a certain number. The number stands for the sensitivity of the grain and is called the ISO value. The larger the number, the more light the grain is able to absorb.
For shots in bright sunlight (for example outside on a sunny day) a 100 ISO film is recommended. A 1600 ISO film is suitable in relatively dark places.
Light meter
To achieve the right exposure cameras are normally equipped with a built-in light meter. A light meter consists of a panel that acts as a semi-conductor light sensor. This makes it extra sensitive to light, which makes it able to make exact data. This data is then used to measure the film and shutter speed.
The size of the lens opening, also knows as the aperture, let's you change the amount of light going through the lens. A part called the iris diaphragm makes this happen. It consists of a series of overlapping metal plates that move at a certain speed. Just like the iris in your eyes, it controls the diameter where the light is captured.
 |
| close-up of a iris diaphragm of a Nikkor 18-55mm lens |
 |
| one 'closed' and one open iris diaphragm |
The Shutter Speed
The amount of time the film is being exposed by light is determined by the shutter speed of the camera. The most common technique is called a focal plane shutter.
You can compare it with the curtains by a window. Before you take a picture, the light is being blocked by the "curtains". This makes sure the film is not yet exposed to any light. Then, when you take the picture the "curtains" open and for a certain amount of time light reaches the film.
To achieve this effect, the camera is filled with gears, switches and springs. When you take a picture, a lever is released and several gears are set in motion. Different shutter speeds are possible by adjusting this mechanism.
 |
| example of a focal plane shutter |
ISO value
But before you can take the shot, you need to know the right aperture and shutter speed. The ideal settings also depends on the size of the light-sensitive grains in the film. Each film has a certain number. The number stands for the sensitivity of the grain and is called the ISO value. The larger the number, the more light the grain is able to absorb.
For shots in bright sunlight (for example outside on a sunny day) a 100 ISO film is recommended. A 1600 ISO film is suitable in relatively dark places.
 |
| a ISO 400 film, with 24 frames |
Light meter
To achieve the right exposure cameras are normally equipped with a built-in light meter. A light meter consists of a panel that acts as a semi-conductor light sensor. This makes it extra sensitive to light, which makes it able to make exact data. This data is then used to measure the film and shutter speed.
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