ISO in Photography: How to Use It Correctly [Actualizado]

ISO sensitivity in photography is one of those settings that, although you use it every day and photo by photo, you may not fully understand how it really works.

In a low-light scene, if you don’t want your photos to be blurry, you’ll almost instinctively raise the ISO and voilaall your problems will have been solved.

But is that really so?

In today’s article, we’ll explain what ISO is in photography and shed some light on this setting that often doesn’t get the attention it deserves.

After all, the quality of your photos will depend on it. You can not lose this!

Before continuing, let me recommend the mega guide that we have prepared to teach you how to photograph in Manual Mode so that you can lose your fear once and for all.

In this way, controlling the ISO will be a piece of cake for you.


What is ISO in photography?

ISO in photography refers to the sensitivity of the camera sensor when it comes to capturing light. It is a scale that determines the degree of sensitivity of the sensor of a digital photo camera with respect to the light that is projected on the sensor.

In analog photography it is the sensitivity of the film used to record the negative of a photograph.

The higher the ISO number, the greater the ability to capture light, the lower the value, the less ability to capture said light.

When you double the ISO value, that is, you go from, say, ISO 100 to ISO 200, you need half as much light to achieve the same exposure.

In this example you can see, with the same shutter speed and same aperture, how the image turns out by modifying the ISO value.

Let’s take a closer look.

Light is the fundamental condiment in any recipe for a good photograph, without it there will be no photo possible.

ISO sensitivity is something like the value that indicates the “amount of light” your camera is capable of capturing in a photograph.

This concept has been inherited from analog photography despite not having much relationship with what it was before and what it is today.

In analog photography, it was not (nor is) possible to adjust the ISO sensitivity from the camera as in the era of digital photography, but each photographic film corresponded to a different ISO value.

Therefore, it was not possible to adjust the ISO from one photograph to another without changing the roll completely.

The sensitivity of these films corresponded to the amount of “silver halides” (something like “pixel size” today) with which said film was manufactured.

The size of each halide crystal on the film indicated the sensitivity and grain that can be seen in the photographs after development.

Today, with digital sensors, silver halides are history (at least for digital photography) and although the name is still used and analog photography is still around, the concept totally changed with the digital revolution.

Analog cameras do not allow you to alter the ISO value.

So, the ISO sensitivity of the sensor measures the reaction of the sensor to a certain level of light in the scene.

This sensitivity is inversely proportional to the amount of light present: the “more light” there is in the environment or scene, the lower ISO sensitivity you can or will have to use and vice versa.

It seems simple, right?

What does ISO stand for in photography?

The name ISO corresponds to the acronym of the organization that gave rise to it: “International Organization for Standardization” or international organization for standardization, that is, as its name indicates, said value is nothing more than a standard adopted worldwide.

How does ISO sensitivity work in photography?

In order for you to understand how your camera’s ISO really works, you need to first understand how your camera’s sensor works, since ISO depends on how it captures light to transform it into a beautiful digital file.

Your camera sensor is that little chip that turns your vision into reality.

It is in charge of transforming the light that reaches it into a photograph.

Just as the film, as I just told you, is made up of silver halides, the sensor is made up of thousands of photosensitive cells that transform the light that passes through the lens.

Upon receiving light, each cell transforms it into electrical current and, after being processed in the brain of your camera (its microprocessor), a digital file is generated, “the photo”, which is stored on the memory card.

The sensitivity of each of these cells is fixed and corresponds to the lowest ISO value that your camera (sensor and processor) are capable of processing.

But if the ISO sensitivity is fixed, how can I increase it with the touch of a button?

In reality, the “sensitivity” of these cells is not being increased since it is fixed, but what is amplified is the electrical current or “signal” that they emit.

If you are shooting a scene where the lighting is poor, when you “amplify” the signal from your sensor cells, you will not only “amplify” the light that managed to reach it, generating a little noise, but you will also amplify the signal of those cells that have been “empty of light”, generating even more noise.

This is where the much hated “noise” is born.

The higher the ISO sensitivity you use when taking your photos, you will not only get clearer photos but also noisier ones.

In the following example, we have kept the same exposure so you can see the effect of raising the ISO value to noise level.

What is noise in images?

Surely, what has become clear to you from the previous explanation is that, at higher ISO, greater noise, especially in the darkest areas.

Noise is the side effect you’ll get by increasing the “sensitivity” before you take a shot.

There are three situations that will cause noise to appear in your photos:

  • Signal amplification: This type of noise is generated, as I just told you, by amplifying the signal of the cells responsible for transforming light into electrical signals, that is, by raising the ISO value. This noise is called electrical or electronic.
  • Temperature: In addition to amplification noise, the temperature of the sensor will also cause noise in your photos. If you make long exposures, or shoot in a burst, the sensor will overheat, which will end up generating the well-known “thermal noise”.
  • The post production: When a photo is underexposed, trying to “lighten” it on your computer will generate noise. The computer will not be able to recover the data that your camera has not been able to capture, so it will “invent” information where there is none, generating noise.
Noise caused by post production

The way in which noise is present in your photographs varies in shape, size and quantity depending on the causes that originate it, the model of your camera, the size of the sensor, etc.

It can be imperceptible or so obvious that it ends up ruining the quality of your photos.

Noise is not always annoying

Anyway, sometimes it’s better to have noise than no photo.

The lens does not always have to be impeccably sharp.

There will be photos or moments in which it is more important to capture the moment despite having noise.

Then there is the issue of the grain, which is often confused but is a different issue.

Inherited from analog photography, it is added with an aesthetic or creative intention. To add a touch of nostalgia or emulate another era, among others.

Here is an example in which we have put enough grain to give you an idea.

Grain used aesthetically or to create an antique effect

How to avoid noise in photography

Here are four ways to reduce noise in your photos:

  1. Keep the ISO as low as possible. “As low as possible” does not mean always keeping it at its minimum value, but adjusting it to the limit of what the lighting conditions of the scene allow you. First try to compensate for the lack of light by slowing the shutter speed or opening the diaphragm. But of course, always depending on what you want to achieve and transmit with your photographs.
  2. In the absence of light, add it. If you can’t compensate for exposure through shutter speed or by opening the aperture all the way, you can try adding more light sources in order to improve lighting and keep your worst enemy, darkness, out of the scene. As I mentioned before, the noise is more noticeable when the darkness is poor.
  3. Avoid the heat. Just as the temperature of the sensor adds noise to your photographs, if you give it a break between shots or do not take too long exposures, you will not only be able to keep this source of noise out (or to a minimum), but also You will increase the useful life of your equipment.
  4. expose correctly. The key to all photography, in addition to its concept and message, is its correct exposure.

How do you achieve proper exposure in photography?

ISO sensitivity is one of the three factors that define the exposure of a photograph.

The other two are aperture and shutter speed.

These three form what is known as the exposure triangle.

As you can imagine, in order to keep the ISO constant (as low as possible) without altering the balance of the exposure triangle, you must make a correct measurement of the available light with the ISO you have set, in order to adjust the shutter speed. shutter and aperture (depth of field) you want to achieve.

  • The shutter speed will allow you convey the sensation of movement or freeze completely a scene.
  • Through the depth of field you can blur completely a fund (achieve a good bokeh) or get a lot of depth of field to shoot some stunning landscapes.

These two elements, as you may have noticed, allow you to add compositional elements to your photos, unlike ISO sensitivity, which will only allow you to capture scenes with low lighting.

You can get lower noise photos using a higher ISO sensitivity if you meter and expose your photos correctly than if you choose a lower ISO sensitivity but the metering and exposure is not correct.

When you have to correct the exposure on the computer, you will end up adding more noise to the photo than if you had used a higher ISO from the beginning but with correct exposure.

Take 5 minutes to analyze the following graph:

Take your time to analyze the graph

The green line marks the values ​​to obtain a correct exposure for a given photograph.

If you want to get a shallower depth of field (greater blur) you should…