One question I’m asked a lot is “Where does all the noise come from when my camera is set to ISO 100?” The answer is simple. The photograph is underexposed.
What is ISO?
Grain vs. noise
Back in the film days, the ISO (or ASA as it was called then) setting was the sensitivity of the film in the camera. While grain existed in every image, high ISO numbers produced more grain because the film had to have bigger chunks of light gathering chemistry.
Today, the same idea applies. ISO in digital cameras refers to the light sensitivity of the sensor. In manual mode, selecting a lower ISO number means there’s a lot of light, to begin with — a sunny day for example. As the light levels lower — like you’d see at dusk, higher ISO’s are required to maintain the aperture/shutter combination used in the sun. Higher ISO means there is potentially more noise, especially in the shadows.
All cameras are not equal when it comes to ISO
Depending on your camera, you might see better performance when it comes to ISO. The more expensive cameras are much better at noise reduction at high and even ultra-high ISO than prosumer cameras are. Full frame cameras generally handle noise more efficiently that crop sensor cameras. It depends on the brand and the price. A Canon 1Dx Mark 2 does a credible job at 51,200 ISO while the Canon 5DSr suffers above ISO 800. Nikon cameras are generally better at high ISO lower noise since they are primarily designed for photojournalists who live with tough light every day.
The noise villain is underexposure
While there are ways to reduce the noise in your image, doing so can ultimately impact your photograph negatively in different ways. It’s because of this that preference for brightening a photograph should first be placed upon adjusting your aperture or shutter speed, ultimately getting a more accurate exposure. Using a light meter like the Illuminati will help you get an accurate exposure every time, whereas your camera’s light meter isn’t as reliable.
Why just not use a lower ISO?
Each camera has what’s called a “Base ISO,” where the quality of images is at its greatest. While using a Base ISO is great for image quality when shooting in ideal lighting situations, it’s not always realistic and it can limit you in terms of how and what you’re able to capture. Low ISO means long shutter speeds in low light. Capturing a moving subject is out of the question. The only solution is to increase the ISO so the sensor gets enough light for a fast shutter speed. Doubling the ISO — say from 100 to 200, allows a shutter speed that is twice as fast — 1/8 of a second at ISO 100 is 1/15th of a second at ISO 200. This only works with the camera in manual mode.
Why do I see noise at a low ISO?
Underexposure. Metering off of a brighter area in a scene will result in a darker photo. Dark photos have to have their exposure increased in Lightroom. Adding exposure to an underexposed photo in post-production adds noise every time.
If you increase the exposure in Lightroom, you’ll get a photograph as if you were shooting at a higher ISO. You’ll see more noise presented in the photograph. The same thing can happen if you’re boosting the shadows in an under-exposed portion of your image.
The left image above is an under-exposed image that I heavily increased the exposure on. The amount of noise here is pretty clear, not to mention distracting. A few seconds later, the image on the right was captured with the proper exposure. Notice there’s virtually no grain, despite it having an even higher ISO setting that its underexposed partner.
Sharpening will also add some digital noise. Move the Luminance slider to the right in Lightroom to help compensate for the noise gain.
How can I avoid noise?
Get the exposure right. Don’t trust the camera’s meter blindly. It’s set to show everything it reads as a middle gray. Use the spot meter. Read a white subject then increase the exposure two to two and a half stops. For example, you take the spot reading off a white shirt like the one below. The reading you get might be 1/125th of a second at f/1.8 ISO 4000. The shirt will come out middle gray. Open up two stops by slowing the shutter speed from 1/125 to 1/60 (that’s one stop) then from 1/60 to 1/30 (that’s two stops more exposure). White is brighter than gray so adding light brightens it.
Ultimately though, noise isn’t a bad thing in photographs. While it might be distracting when you’re editing something at 100% zoom, ultimately, your client will likely never notice. I’ve never once had a client call me and say “there’s too much noise in this photograph.” Ultimately, noise is in every photograph, whether you see it or not!
As new camera technology continues to evolve, shooting at higher ISO figures becomes more and more of an option for photographers. And while noise will always be present, there are easy ways to minimize it during and after your photo shoot.