Monday, 01 January 2018 14:46

The shutter and time scale

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In photography, the shutter is the mechanical or electronic device that has the task of checking how long the sensor (in digital cameras) is exposed to light.

By making a parallel with the human eye, while the iris represents the diaphragm, the eyelid gives an idea of ​​the shutter.

The shutters can be classified into two types:

1. Central obturators

2. Curtain shutters

The first type corresponds to all the shutters equipped with lamellae arranged in a radial pattern, similar to those of the diaphragm.

The second type is a shutter composed of two surfaces of fabric or metal arranged parallel along the focal plane, which slide vertically forming a slot that allows light to pass.

If the time required is slow, the first curtain reaches the end of the stroke and consequently the second part covers the film ending the exposure.

In the case of faster times, the second curtain is operated during the stroke of the first, so the film is not exposed simultaneously throughout the frame, but only through the slot formed by the delay between the first and second curtains.

The shutter, together with the diaphragm (which regulates the intensity of light), is an indispensable factor for determining correct exposure, the right adjustment of the diaphragm aperture combined with the right adjustment of the shutter speed will allow to impress the film or the sensor exactly with the amount of light required (intensity x time) for perfect exposure.

The shutter speed can be used creatively, in fact, by choosing a slow tempo you can capture a subject and enhance its movement (creative blur), or by choosing a fast tempo you can fix (freeze) a moving subject and increase the sharpness of the 'image.

In modern cameras, shutter times are selectable from a ring or, in electronic devices, from buttons or digital controls.

A typical series of shutter speeds (or speeds) in fractions of a second is as follows:

8 4 2 1 1/2 1/4 1/8 1/15 1/30 1/60 1/125 1/250 1/500 1/1000 1/2000 1/4000

In the time scale each value is about half of what precedes it and about twice that of the next one.

Normally the values ​​below the second are displayed only with the divider: 1/125 becomes 125.

As for the diaphragm scale, the interval between the different shutter speed values ​​is indicated in stop jargon.

By increasing / decreasing by one stop the shutter speed doubles / halves the amount of light that reaches the sensitive support.

For example, if the shutter speed is increased by 1 stop, without changing the aperture value, the exposure calculated by the exposure meter is increased by 1EV, which means doubling (2X) the amount of light entering through the aperture. 'target.

But if at the same time we close the aperture of a diaphragm by a 1 stop, so that we halve the amount of light that penetrates through the lens, we have a compensation and the exposure value (EV) remains unchanged.

 

 

Articolo tratto da wikipedia

Read 1366 times Last modified on Monday, 01 January 2018 16:35
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