One of the parameters that give the most headaches to photographers is the ISO sensitivity. First of all because we don't know what it is and when we start taking pictures, we tend to leave it on automatic, so that as a result, some pictures are good, while others leave noise in the image. But when we progress and we start to use the ISO value well, we discover new possibilities but especially the control. And it is no longer the camera that controls you but you who control the camera. We will see what exactly this concept means and how to properly set the ISO to get the most out of your work.

A little history: the origin of ISO sensitivity

Those of you who are from the film era must surely remember the ASA standard for photos. The ASA (American Standard Association) standard was a photo sensitivity standard established to achieve a sensitivity below or above the impact of light on traditional photo film. You could say it was the mother of the ISO standard.

Then with the advent of modern digital cameras, the international reference ISO (International Organization for Standardization, an international standardization system for products from various sectors) adopted the ASA standard, while maintaining a scale of values similar to the then ASA standard. This led us to switch from ASA 400 film to ISO 400 film, by analogy, in the midst of the digital revolution of recent years.

ISO sensitivity: what is it and how to use it?

ISO sensitivity is the ability of the image sensor to be more or less sensitive to ambient light, in other words it is the amount of light that it must recover. All image sensors start from a basic sensitivity that corresponds to the lowest ISO value available on the camera (we will exclude here the values of the forced ISO). Several years ago, for example, the base value was ISO 200 on Nikon cameras and their values therefore ranged from ISO 200 to ISO 1600. Canon, on the other hand, started with an ISO 100 value, but Nikon has since switched to a base ISO value of 100.

• The lowest values 100, 200, etc. imply a high "resistance" to light and are therefore generally suitable for situations with strong ambient light present
• The higher values 1600, 3200, etc. imply less resistance to light and are therefore more suitable for situations with low ambient light, in general.

Let's imagine that the image sensor is like a cube that can fill with light. When the shutter is pressed, the light passes through the diaphragm (more or less closed) to reach the sensor all the time the shutter remains open (1/250 second, 1/125 second or several seconds). During this time, the "cube" fills up depending also on the ISO sensitivity.

ISO sensitivity and exposure triangle

Until now, we have mentioned the ISO in isolation, as an element that plays a direct role on the good exposure or not of the photo. But its influence, although direct, is linked, as we can guess, to two other parameters: the shutter speed and the aperture.

Ultimately, to take a picture with your camera, you will need a certain amount of light and communicate to it, in some way, what sensitivity it should adopt in relation to the light. This is achieved by choosing a certain shutter speed, a certain aperture, and of course the ISO sensitivity.

Although your objective is not to expose well but to take a picture -I insist-, you must know the technique. And it is only by setting these three values that you will get enough and adequate light to overexpose or underexpose the image as you wish.

Also, you can produce various visual effects by adjusting the f-stop (an open f-stop will mean a shallower depth of field, while a closed f-stop will cause the opposite). By adjusting the shutter speed, you can, among other things, freeze the movement of an element in the scene. And finally, with the ISO sensitivity, you will correct the two previous settings in order to enjoy a correct exposure.

How to use the ISO sensitivity in digital photography

We must then ask ourselves the following question: how to use ISO effectively?

First of all, ISO sensitivity is one of our greatest allies for unblurred photos. As we have seen, in very bright situations, we will use the lowest possible ISO value, while we will raise it for darker situations. Sensors have evolved enormously in the last few years and from compacts to SLRs to CSCs with interchangeable cinema lenses or EVILs, almost all mid-range cameras have good sensors, including high-end compact cameras. That's why raising the ISO in situations with less light will allow you to opt for a slower shutter speed and avoid blurred photos, without too much fear of digital noise.

Next, the noise, precisely. Noise at high ISOs used to imply that using values above 800 gave very poor quality images, with a lot of noise and little detail. Even if the definitive solution has not yet appeared, it is still possible to use ISOs higher than 1600-3200, or even 6400, on many cameras, and still enjoy acceptable image quality, in many cases. Basically, the better the camera, the higher the ISO value you can use for these low light conditions.

Finally, although they are based on a standard, ISO values vary slightly from one camera model to another, due to various factors. This will give slight but observable differences in exposure results with the same cinema lens on different cameras using the same shutter speed and ISO value.

Conclusion

In general, it's best to use the lowest possible ISO value because you'll enjoy more detail, sharpness, better color and less noise. That being said, don't be afraid to use a high ISO in situations that require it because as we said, sensors have improved a lot in recent years. My best advice: know your camera and make the most of its capabilities.