What are the basic metrics for good photos?

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Without light we would not see anything and would not even catch a film emulsion or a digital camera sensor.

Light is the most important element of photography. It must not be too much or too little. We decide how much light we use when choosing an exposure. And what is this exposure?

What are the basic metrics for good photos?

Exposure is the process of exposing a sensor or film to incident light and is measured in units labeled EV (Exposure Value).

Exposure affects three basic factors: sensitivity, time and aperture. The exposure time indicates how long the light affects the sensor.

The aperture value indicates the diameter of the aperture through which the light passes through the sensor. These two factors affect the total amount of light incident on the sensor. A third factor is the sensitivity, which indicates how sensitive the sensor or film emulsion is to the incident light.

Take a fraction of a second

The exposure time is given in seconds and is based on the so-called exposure time scale, which is a sequence of consecutive values.

15, 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, 1/8000

You have certainly noticed that each grade is half the size of the previous one, except for some exceptions, for example, the use of “appropriate numbers”. Importantly, changing the time by one value changes the amount of incident light by 1 EV.

The aperture is a mechanical device that is inside the lens and affects the amount of light passing through it is referred to as the aperture number f / number or number . As with time, the aperture number has its own scale.

F1; F1,4; F2; F2.8; F4; F5.6; F8; F11; F16; F22; F32; F45; F64

Again, here you can see the dependence of consecutive numbers, for the aperture number, too, the change of one value changes the amount of light by 1EV. The aperture must be aware that the higher aperture number means less incident light – at F1, the aperture in the lens is maximally open, then the aperture F64 is then maximally closed.

What are the basic metrics for good photos?

The ISO sensitivity determines the photosensitivity of the sensor and is achieved in films of different sensitivities by using another sensitive emulsion. Sensors are achieved by varying sensitivities by amplifying the signal read by the sensor.

The sensitivity also refers to the above-mentioned rule of the effect on the amount of light in a unit change. A number of sensitivities are as follows:

ISO 50, ISO 100, ISO 200, ISO 400, ISO 800, ISO 1600, ISO 3200, ISO 6400,

There is reciprocity between the three variables, if one is increased, another must be reduced to maintain the same exposure and vice versa. Better understand from the following table.

time (s)1/5001/2501/10001/250
the aperture (F)22.824
Sensitivity (ISO)100100200200


In practice, it is possible to use a large number of combinations of three variables which will lead to the same result = correct exposure . Controlling these variables is a way to get a good photo that you can work with .


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