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Sensor sensitivity

Heures
The focal

This article on sensor sensitivity is part of a series of 4 popular articles concerning adjustable parameters on cameras with the aim of optimizing the quality of photographs taken for photogrammetric use in particular for the application ContextCapture of the Bentley Systems.

When shooting, the photographer can adjust 4 main parameters to compose and control the exposure of his image:

Sensor sensitivity

This is the case's ability to be sensitive to light. A large (3200 or 6400) high-performance ISO mount allows you to photograph inside without flash. In sports or animal photography, this is a key criterion.

The ISO sensitivity measurement is identical to the ASA measurement from which it is derived.

Between each ISO sensitivity, there is a multiplier factor that is usually double. Current values are: 100, 200, 400, 800, 1600, 3200, 6400, 12800.

However, most boxes offer intermediate values: 320, 640, 1250, 2000, 2500, 4000, 5000, 8000.

To understand the functioning of ISO sensitivity, it is necessary to know that the sensor of your reflex has a basic sensitivity: 100 (Canon) or 200 ISO (Nikon). When it is desired to increase the ISO sensitivity in the case settings to compensate for a lack of light, the basic signal of 100 or 200 ISO is amplified by an electronic circuit (10 times to obtain 1000 ISO for example). It is for this reason that there is an appearance of electronic noise or grain when using significant sensitivities (more than 3200 ISO).

To be retained

The choice of ISO sensitivity is a compromise: do I need speed? A small opening to obtain an important sharpness area?

Depending on the subject to be photographed, one adapts each parameter: ideal being to use the lowest ISO sensitivity possible to obtain better image quality.

Beware of the "auto" mode that automatically selects sensitivity for you: in this configuration you may take photos with too high sensitivity that would cause a noise phenomenon in your photos and therefore a poor quality which would seriously harm the result of photogrammetric modelling.

And for ContextCapture ?

A sensitivity beyond 400 is not recommended, a grain will be visible when zoomed out. It should be kept in mind that the software performs its pixel analysis!