ISO sensitivity is one of those settings that, although you use daily and photo by photo, you may not quite understand how it really works.
In a low light scene, if you do not want your photographs to move, almost by instinct you will upload the ISO and “voilà”, all your problems will have been solved. But is that really so?
In today's article, we will shed some light on this adjustment that is not usually given all the attention it deserves. After all, the quality of your photographs will depend on it. You can not lose this!
ISO SENSITIVITY: WHAT IS IT?
Light is the fundamental condiment in every recipe for a good photograph, without it there will be no photo possible. The ISO sensitivity is something like the value that indicates that "amount of light" is necessary for your camera to capture a photo.
This concept has been inherited from analog photography despite not having much to do with what it was before and what it is today. In analog photography, it was not 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 change 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 "the size of the pixels" of today) with which said film was made. The size of each halide crystal in the film indicated the sensitivity and grain that can be seen in the photographs once revealed.
Nowadays, with digital sensors, silver halides are history (at least for digital photography) and although the name is still used, the concept changed completely.
Analog cameras do not allow you to alter the ISO.
Then, the sensor's ISO sensitivity measures its reaction 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 use and vice versa. It seems simple, right?
The ISO name 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, this value is nothing more than a worldwide adopted standard .
HOW DOES IT WORK?
In order for you to understand how your camera's ISO really works, it is necessary that you first understand how the camera's sensor work since, the ISO depends on how it captures the light to transform it into a beautiful digital file.
The sensor of your camera is that little chip that turns your vision into reality. He is in charge of transforming the light that comes 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 through the lens.
Upon receiving light, each cell transforms it into electrical current and that, after the brain of your camera (its microprocessor) is processed, 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) is 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 electric current or “signal” that they emit.
If you are photographing a scene where the lighting is low, when you “amplify” the signal from the cells of your sensor, you will not only “increase” the light that managed to reach this sensor, but generate some noise, but also amplify the signal of those cells that have been "empty of light", generating even more noise. This is where the hated "noise" is born.
The higher the ISO sensitivity you use when taking your photographs, you will not only get clearer photographs but also louder ones.
SENSITIVITY AND NOISE
Surely what has become more clear to you from the previous explanation is that, the higher the ISO, the greater the noise, especially in the darkest areas. Noise is the side effect that you will achieve by increasing "sensitivity" before taking a shot.
There are three situations that will cause noise to appear in your photographs:
Signal amplification: this type of noise is generated, as I just told you, by amplifying the signal of the cells responsible for transforming the light into electrical signals. This noise is called electrical or electronic.
The temperature: in addition to the noise by amplification, the temperature of the sensor will also generate noise in your photographs. If you make long exposures , or shoot in burst, the sensor will be overheating, which will eventually generate the known "thermal noise."
Post production: when a photograph has been under exposed, when you try to “clarify” it on the computer, you 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.
The way in which noise is present in your photographs varies in shape, size and quantity depending on the causes that originate it, your camera model, sensor size, etc. It may be imperceptible or so obvious that it ends up ruining the quality of your photographs.
Anyway, noise is not always annoying, if you learn to live with it, you can use it and take advantage of it. Noise does not always ruin a photograph, often the power.
How to avoid it:
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. First try to compensate for the lack of light by decreasing the shutter speed or by opening the diaphragm. But of course, always depending on what you want to achieve and transmit with your photographs.
In the absence of light, add it: if you cannot compensate the exposure by shutter speed or by opening the diaphragm to the fullest, you can try to add larger sources of light so as to improve the lighting and ward off your worst enemy,the darkness of the scene. As I mentioned before, the noise is most noticeable when the darkness is poor.
Avoid heat: just as the temperature of the sensor adds noise in your photographs, if you take a break between taking and taking or do not make too long exposures, you can not only keep this source of noise (or at a minimum) but also In addition, you will increase the life of your equipment.
Propose correctly: the key to any photograph, in addition to its concept and message, is its correct exposure.
THE IMPORTANCE OF EXPOSING CORRECTLY
ISO sensitivity is one of the 3 factors that define the exposure of a photograph. The other two are the aperture of the diaphragm and the 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 and the aperture of the diaphragm ( depth of field ) you wish to obtain.
The shutter speed will allow you to convey the sensation message or to completely freeze a scene. Through depth of field you can completely blur a background (achieve a good bokeh) or get a lot of depth of field to photograph stunning landscapes. These two elements, as you may have noticed, allow you to add compositional elements in your photographs unlike the ISO sensitivity that will only allow you to capture scenes with poor lighting.
You can obtain photographs with lower noise using a higher ISO sensitivity if you make a correct measurement and exposure in your photographs than if you choose a lower ISO sensitivity but the measurement and exposure is not correct. When you have to correct the exposure on the computer, you will end up adding more noise in the photo than if you had used a higher ISO from the beginning but with a correct exposure.
Take 5 minutes to analyze the following graph:
The green line marks the values ??to obtain a correct exposure of a particular photograph. If you want to obtain a lower depth of field (greater blur) you will have to compensate for the “extra light” that your camera will capture by increasing the shutter speed (Pass from 1 to 2). This will happen to you if what you want is to freeze the movement.
Now, if what you want is to achieve a greater depth of field (greater sharpness) and continue over the green line that marks a correct exposure for our dummy photograph, you will have to compensate for the lack of light resulting from closing the diaphragm, reducing the shutter speed (Pass from 1 to 3). In this way, you will not be able to freeze the movement but, you will gain a lot of depth of field, very useful for example, in landscape photography.
Now, if you wanted to achieve a correct exposure but keeping the diaphragm very closed in order to obtain depth of field (f / 16) and, at the same time, use a speed of 1/100, the only way for you to achieve a correct Exposure is increasing ISO sensitivity (ISO 800). The red line marks the new correct exposure. (Go from 1 to 5).
On the contrary, if with the same values, you would also like to use a very low ISO sensitivity, the only thing you will achieve is a sub exposed photograph (Pass from 1 to 4).
WHAT SENSITIVITY TO USE?
The tendency to keep ISO sensitivity as low as possible is just that, a trend. Remember that the light will vary from one scene to another so, in each of them, you must make a good measurement and adjust the ISO value so you can get the picture you are looking for.
Forcing a photo to use a very low ISO sensitivity will only cause, when sub or over-exposing your photos, when editing them you end up introducing even more noise than if you had adjusted the ISO a little higher. The key to fighting noise is correct measurement and exposure. Never forget!
Noise is not everything
TIPS TO USE ISO CORRECTLY IN YOUR PHOTOGRAPHS
Now that you have read all the theory about ISO sensitivity, or all that may interest you at this time in your life as a photographer, let's review some tricks and tips that will be very useful to bring everything learned to the practice:
The ISO to the minimum possible: always try to use the minimum possible ISO sensitivity, that is, the one that allows you to take the picture you are looking for and according to the present lighting that allows you an optimal exposure. In this way, by correct exposure and an ISO to the minimum possible, you will reduce the noise considerably.
Evaluate all the variables: before preparing to raise the ISO sensitivity, try to see how you can avoid it by adjusting the other two variables that define the exposure: depth of field and shutter speed. Do not rule out the use of a tripod if necessary.
Keep an eye on the exposure : Always before shooting, remember to correctly measure the light present in a scene. Never give up correctly exposing just "increasing ISO sensitivity." It may seem like an easy way to increase the ISO, but if you take the job of exposing correctly, the quality of your photos will increase considerably.
Do not fear noise: no matter how hard you try to minimize it, do not fear noise. In many situations it will be impossible to eliminate it either by the camera you are using or by the low ambient light. Never stop taking a picture, even if the noise is more than you would like, after all, ultimately, you can reduce it later with some editing program on your computer.
Always shoot in RAW: as I just told you, you can always try to reduce the noise of your photographs using some editing program. You will get much better results if you work directly on the digital negatives than if you do it on the Jpg. The RAW format saves much more information since it is not compressed, which will allow you to recover much more information than in Jpg.
Do not use AUTO ISO: although almost all cameras allow you to configure the automatic ISO selection option, I do not recommend that you use it for two reasons: the first one, because your camera will never make better decisions than you when choosing the best possible and second configuration, because the cameras are configured to measure the light as if everything in the scene was neutral gray (an average of light and dark tones) so when measuring the sensitivity to use, it will also do so on average and in Most cases end up wasting a lot of potential on your sensor to capture all the tones it is capable of, both dark and light.
Never expose yourself: as I mentioned earlier, it is preferable to raise the ISO sensitivity and generate a little more noise than using a lower ISO and then correct the exposure on the computer. As good as the editing programs are, they will always generate noise if the shot has not been correctly exposed, therefore, it exposes correctly and always towards the lighter tones.
Define your tolerance to noise (and that of your camera): beyond all the information you can get by reading this article and other articles published across the Internet, the one that defines the optimal ISO is you. You must consider two things: What is the maximum noise you are willing to tolerate? And do you know how your camera works at different sensitivities? The key to mastering the ISO sensitivity is your: perform all possible tests with your camera so that you know how it works and how it processes noise. Once this is done, you will be in a position to know what is the optimal ISO with which you will try to work on each of your shots.
As always, the key to everything in photography is you: you make the decisions, you plan to make them, you define the composition, define what is tolerable and what is not. You are the owner of your own creativity. The key to success in photography, it's always you.
FINALLY, WE TEAR DOWN A MYTH:
Do not think that because the sensor of your camera is small, you will not be able to obtain spectacular photographs without much noise. The small sensors are not louder, or yes, but not because they are not able to take pictures without noise but because the ISO sensitivity that the manufacturer assigns to them is not really such.
What I mean by this? Remember that I told you that the ISO was a standard, well, all cameras regardless of their size and type of sensor work with the same standard although it is not valid: compare the ISO 800 of a Full Frame camera with the ISO 800 A camera with an APS-C sensor is as valid as comparing pears with bananas.
"Small sensors have a noise level similar to a larger one in the same amount of light"
Let's do some calculations:
The clipping factor of a Nikon APS-C sensor for example is 1.5 with respect to its Full Frame torque. That is, the Nikon Full Frame sensor is 1.5 times larger than in an APS-C camera. This clipping factor is well known as it is generally applied to calculate the focal length of a target.
A 200mm lens in a Full Frame is equivalent to an effective focal length in a Nikon camera with a 300mm APS-C size sensor (200 * 1.5 = 300).
However, this clipping factor, not only must be used to calculate the equivalent focal length but also, it must be used to also calculate the equivalent effective ISO sensitivity.
An ISO sensitivity of 800 in a Full Frame Nikon is equivalent to an ISO of 350 in an APS-C. If you take a picture in both a Full Frame and an APS-C with these ISO values ??set, the noise level will be the same before the same amount of light in the scene.
ISO in APS-C * Trimming factor (1.5) ²
To compare the ISO 800 of a Full Frame that is the standard against an ISO 800 of an APS-C is to literally buy pears with apples.
At the same amount of light and using equivalent ISO sensitivities, no matter the size of the sensor, the amount of noise will be the same. That is why the smaller sensors seem louder, although in reality they are not, only that the ISO sensitivity of one and the other must be converted to be comparable.
If you got here, you just read more than 3000 words on how to use ISO correctly. Congratulations, I hope you found this tutorial useful. As always, the best way to help me keep writing is by spreading this article through your social networks, so other friends can also take advantage of it.
