photo: © Sasha Zilov - taken on January 5, 2025 with Sony α7C II - aperture ƒ/4.5, ISO 1600, shutter speed 0.004s
There are a few immutable laws in photography. Small apertures? Large depth of field. Large apertures? Small depth of field. Fast shutter speeds freeze action, slow ones create movement. And high ISOs? They give you noise. But honestly: that's less dramatic these days than it used to be.
High ISO has always been a compromise, and while modern technology has erased many of the old limitations, the topic remains a source of confusion and debate. Let's dissect it.
What is ISO
The term ISO comes from the days of analog film. In the past, film manufacturers each had their own ratings for light sensitivity. That was confusing, so a standard was developed: ISO (International Standards Organization). This system gave photographers a universal benchmark for knowing how light sensitive a roll of film was.
Film
With film, light sensitivity was built into the roll. An ISO 100 film was ideal for sunny days, while an ISO 800 film was suitable for dimly lit situations. But you were stuck with that choice. Did you want to switch between indoor and outdoor situations? Then you often had to either work with two cameras or complete a roll before you could switch.
Digital
Digital cameras don't use film, of course, so that ISO number is actually an equivalent: the number tells you how sensitive your image sensor is to light, compared to the equivalent pack of film.
This allows us to simply set the ISO we want to use depending on the lighting situation. The only real problem with the digital ISO system is that we sometimes forget to change the ISO when going in and out of different lighting situations.
It is of course infinitely useful to be able to change the light sensitivity of your camera's image sensor. Every photographer faces a situation where the light is too low for low ISOs, and has the option to adjust that setting when necessary. But some photographers hesitate to do this and opt for one instead larger aperture or slower shutter speed, or even to turn on the flash.
And there are certainly situations where this is appropriate: for example, shots where there is no motion can be photographed at long shutter speeds and low ISOs, as long as the photographer has a tripod to stabilize the camera during that longer exposure. And large apertures (small f-number) are also an alternative, provided the depth of field is not important.
Flashing is another alternative, if done properly. Direct flash can be very unsightly and cause washed out faces, red eyes and black shadows, but if you use a external flash you have, it can be reflected or diffused, meaning the light looks much more natural.
What causes noise?
If you don't have an external flash, or if you need a greater depth of field, or if there is movement in a scene, it is better to choose the higher ISO.
Some photographers are still hesitant to do that and opt for small camera shake or motion blur anyway so they can keep that ISO number low. That still stems from an age-old belief, once based on very real concerns, that high ISO photos are of poor quality.
With analog film, higher ISOs produced larger silver halide crystals, resulting in visible grain. In digital photography we call this effect noise. However, the cause is different: noise is caused by the ratio between signal and noise in the sensor. The less light available, the more random variations become visible, especially in dark areas.
Some photographers are still hesitant to use high ISOs and still opt for minor camera shake or motion blur...
Now with digital we get a similar visual effect with higher ISOs, except the explanation for this is completely different. Instead of a “grain,” we call it “digital noise,” which looks similar in that both grain and digital noise have a sort of gritty or grainy appearance.
Digital noise is always the same size, because pixels remain the same size regardless of the ISO value. The amount of noise increases at higher ISOs, and it is most visible in the blue channel. This distinguishes digital noise from film grain, which had a neutral color and varied in size with ISO.
Even today, high ISOs can still cause photo quality issues even in modern cameras.
Modern solutions
Nowadays, the limitations of ISO are much less severe. Cameras have more advanced sensors and more powerful processors that reduce noise in JPEG images. For example, if you have a brand new system camera you probably won't notice any noise until you reach those very high ISOs. But if your primary camera is a smartphone, with a very small sensor, you'll start to notice noise at ISOs in much lower ranges.
Full frame sensors and stacked sensors deliver better performance at high ISOs, and post-processing software makes it easier than ever to reduce noise in RAW images.
Yet it remains a personal choice. Some photographers tolerate some noise, while others try to avoid it at all costs. This can even lead to poor decisions, such as lowering the shutter speed or opening the aperture to a point where the shot becomes blurred or incorrectly exposed.
How do you test your camera?
An easy way to understand how your camera handles noise is to experiment yourself:
- Choose a stationary object in a moderately lit environment, such as a daylight room.
- Use a tripod and set the ISO value to 100.
- Take a photo and gradually increase the ISO, while only adjusting the shutter speed. This way you keep the depth of field consistent.
- View the images at 100% magnification and determine the ISO up to which you find noise acceptable.
This will give you a reference point to work with. Just keep in mind that it's better to only change the shutter speed for this experiment, because when you change the aperture you change the depth of field in the image, which makes it harder to compare the low ISO shot to the higher ISO shots.
Do you find yourself in a situation while photographing where you have to set the ISO higher than you normally would like? Then consider alternatives such as a lens with a larger aperture or the use of extra light, for example via an external flash.
Tips to keep noise out of your recording
There are ways to reduce the amount of noise in your photos, even at ISO values you don't quite like.
Histogram
The first tip is to use the histogram. If your camera shows you the histogram before you take the photo, you can use that information to take a photo that is less likely to contain noise. Specifically, you want to “expose on the right.”
That means you want the histogram to be slightly skewed to the right, with the highest peaks on the right, but without clipping in the highlights. In other words, the graph must taper off before it reaches the edge, rather than being cut off abruptly. Using this technique can reduce the amount of noise you capture, especially in low-contrast shots.
Post-processing
Don't forget that you can also unintentionally increase noise in post-processing. Illuminating underexposed areas in an image can increase noise, so it's best to use the "shoot to the right" technique. And this problem becomes more apparent the higher the ISO is.
Since you don't have the opposite problem (you don't create noise when you darken shadows), that's a good reason to lean toward slightly overexposing in low-light situations. Remember that you can always darken a slightly overexposed image without creating noise.
Textures
Noise is less noticeable in highly textured areas, such as leaves or rocks, than on smooth surfaces such as a water surface.
Creative use of noise
Noise isn't always bad. It can give a photo a raw, journalistic character or a nostalgic, cinematic feeling. Some modern cameras even have creative controls such as Grain Effect to simulate the appearance of film grain.
Instead of avoiding it at all costs, try to embrace noise. Sometimes it actually contributes to the aesthetics of a photo.
Even if you are intensely uncomfortable with noise, you can increase your ISO beyond your reference point and try to photograph situations where you include noise in the composition. You might surprise yourself with some of the beautiful effects you can achieve not only despite the noise, but because of it.
