Increasing the ISO for low-light photography has recently become less of an issue for various reasons. Nevertheless, if you want to capture action, you should understand it to achieve better photos.
Improvements in image stabilization have partially made increasing the ISO less necessary in some circumstances. Then, sensor technology has vastly improved image quality at higher ISOs. In addition, the superior noise reduction in several programs makes low-light photography far more accessible.
It’s common knowledge that as you increase the ISO of the camera, more noise is seen in the photograph. However, it's also a common misconception that increasing ISO causes more noise. It doesn’t.
What Is ISO?
ISO stands for International Organization for Standardization. We see it everywhere as organizations try to find common standards for everything from customer service levels to candles’ sooting behavior. In photography, we can think of it as the camera's sensitivity to light.
Increasing the ISO setting makes the camera's sensor more sensitive, thus allowing it to capture more light in less time. In other words, if you put the ISO up, you can achieve a faster shutter speed or, less commonly, a smaller aperture.
There is a pay-off, however. The higher the ISO, the more likely we are to see noise in the photo.
If I were being pedantic, that’s not strictly accurate. Nevertheless, it is a simple way of understanding it.
Okay, I'll Be Pedantic.
f I don’t write this, someone will complain. Pedants will point out that increasing the ISO doesn’t make the sensor more sensitive, nor does it increase noise.
In the movie Back to the Future, Marty McFly turns up the electric guitar amp to its full volume. Before he strums his guitar and the sound from the massive speakers throws him across the room, you hear a humming. That is noise being generated within the amplifier. If you have a hi-fi at home and turn the volume up full with no music playing, the speakers emit a hissing sound. The same principle applies when we increase the ISO in our cameras. However, we cannot hear it. Instead, we see the noise in the image as graininess.
When increasing the ISO, we are turning the gain on an amplifier inside the camera. We've done that because the original signal was weak (due to insufficient light), and increasing the ISO boosts that signal. There's a drawback. Doing that will also amplify any noise. Therefore, the proportion of noise increases (this is known as the signal-to-noise ratio). Consequently, that noise appears more prominent in the image. I'll explain more about noise shortly.
Understanding the Numbers
If you think about the ISO increasing the sensitivity of the image sensor, the lower the number, the less sensitive it is to light. Higher numbers mean increased sensitivity, but there is a compromise of more noise.
With each step of ISO, you need half the amount of light to achieve the same exposure.
For example, ISO 100 and 1/250 second is the same exposure value as ISO 200 and 1/500 second, ISO 400 and 1/1000 second, and so on.
The Best ISO to Use
Base ISO refers to the lowest ISO settings on a camera at which the sensor can achieve its best signal-to-noise ratio and, consequently, its full dynamic range. Typically, your camera's base ISO has no amplification. In other words, you get the lowest possible noise at this setting.
(It’s worth noting that some cameras have extension ISOs that enable even lower settings, but there is a drop in image quality if you use those.)
Knowing your base ISO is crucial because it allows the camera to produce the highest image quality with minimal noise.
What is your camera's base ISO? It varies from camera to camera. While it is often ISO 100 (e.g. most Canons, Nikons, and Sonys), on some cameras it is ISO 64. Meanwhile, with my OM System OM-1 and other Micro Four Thirds models, it is ISO 200.
How Big Is Your ISO Range?
Some cameras have ISO ranges from 100 to 6,400. Meanwhile, some newer and more advanced models can go much higher. Mine has a range from ISO 80 to ISO 102,400. However, ISO 32,000 and above, and anything below ISO 200, are extension ISOs. These are digitally enhanced ISOs that give you a greater ability to take images at otherwise unobtainable shutter speeds. However, there is an image quality payoff, with dynamic range falling and noise increasing.
ISO’s Impact on Exposure
ISO is one of the three exposure variables, along with aperture and shutter speed, that I wrote about in recent articles. Increasing the ISO usually allows for faster shutter speeds in low-light conditions. However, albeit less commonly, it can also be used to achieve smaller apertures.
ISO Usage
As a rule of thumb, low ISOs (80–200) are ideal for bright conditions and when you want the highest image quality. They also help you achieve long exposures. Meanwhile, medium ISOs (400–800) can be useful for indoor photography or shooting on cloudy days. A high ISO (1,600 and above) is usually necessary for very low-light conditions, such as night photography or indoor sports, when you want to stop the action.
Noise Tests
Whenever I buy a camera, I test it to see how well it performs at different ISOs. I do this both with JPEGs and raw files. The JPEGs are processed within the camera and have noise removed. Raw files rely on you processing them to remove the noise.
What follows are my JPEG tests. These images are "straight out of camera" (SOOC) with no development applied. They were shot in aperture priority mode at f/8, with no exposure compensation. I increased the ISO by 1 stop each time.
I started with the camera's base ISO of 200, at which it performs best. The image is nice and clean, as would be expected.
Next, I doubled the ISO to 400. There's very little difference.
Now, ISO 800. Again, it's a nice, clean image.
Here's an ISO 1,600 SOOC image. You will notice that the blacks are starting to be not quite so deep, and zooming in on the image (click on it to see), there is some visible luminance. However, the photo is perfectly usable.
Here's ISO 3,200. There's very little visible difference between this and ISO 1,600.
This next image was shot at ISO 6,400. Close examination shows some luminance noise, but once more, this image is usable.
Here's ISO 12,800. The image is usable, but the noise is becoming more apparent.
ISO 25,600 is the highest native ISO on my camera. Luminance noise is more visible, but the graininess isn't ugly. I don't ever have a call to shoot at this high an ISO.
Although all the images are usable, if we compare the ISO 200 image (left) with the one shot at ISO 25,600 (right), we see a difference.
Exposing to the Right
There's a good thing about knowing you are turning up an amplifier. If you increase the exposure, you are letting more light into your camera. Therefore, the sensor transmits more electronic signals, helping to drown out the noise. This is known as exposing to the right (ETTR). However, increasing the exposure runs the risk of blowing out the highlights.
Becoming familiar with your histogram is important here. It will help you control your exposure so you are not over-exposing too far. If you are unfamiliar with the histogram, I wrote an article about it four years ago that you can read by clicking here.
In the left-hand image below, at ISO 25,600, I increased the camera's exposure by 0.7 of a stop and then reduced it again in Lightroom. On the right is the same ISO 25,600 image I showed above with no exposure compensation. Making this slight adjustment makes a visible difference to the image, reducing noise and improving the dynamic range.
More About Noise
Noise in digital photography refers to the random variation of brightness or color information in images. It manifests as the unwanted grainy or speckled appearance in photos, and it is usually more noticeable in darker areas. You can see these in the samples above.
There are two types of noise: luminance noise appears as gray graininess, affecting the brightness of pixels. That is usually considered more acceptable than chrominance (also known as chroma, or color) noise, which appears as ugly color speckles and banding. Chrominance noise affects the color of pixels.
High ISO settings are not the only cause of noise in a photo. Longer exposures can introduce noise due to the camera’s sensor heating as electricity flows through it. Also, smaller sensors found in compact cameras and phones tend to produce more noise than the larger sensors in DSLRs and mirrorless cameras.
However, recent advancements in sensor technology have greatly reduced the amount of noise produced. Furthermore, new image processing technologies do an amazing job of removing noise.
Noise Reduction Techniques
Many cameras have built-in noise reduction settings. Some cameras have two settings, one for removing high ISO noise and the other for noise generated during long exposures.
There is some fabulous noise reduction software out there. I think the best is currently found in the recently released DxO PureRAW 5, which does an amazing job of cleaning up an image. It works as a plugin for other programs such as Lightroom, but can also be a stand-alone app.
There are plenty of other programs out there that do a good job, too. ON1 Photo RAW has an effective NoNoise feature. Topaz DeNoise AI is popular and works well. Lightroom also has built-in noise reduction. It's good, but I find using one of the other programs as a plugin gives superior results.
How Do I Change the ISO?
Most cameras have an ISO button. Press that and turn the adjustment dial (sometimes called the command dial). You should see it changing through the viewfinder or on the back LCD screen. Some cameras don’t have a button, and ISO adjustments are made through the menu.
Auto ISO
There are some circumstances where I am photographing flying birds in changing lighting conditions. I use aperture priority because I want to shoot at a wide aperture, enabling a shallow depth of field and a faster shutter. I know I need 1/2,500 second minimum shutter speed, and it is often bright enough where I live to achieve that at my camera's base ISO of 200. However, sometimes the bird is not well lit. In that case, I can set the camera so that 1/2,500 is the minimum shutter speed. However, I don’t want the ISO to go above 12,800, so I limit that too.
When there is insufficient light to achieve 1/2,500 at ISO 12,800, the camera allows the shutter to slow below 1/2,500.
This isn’t the only way of working, and some photographers have other approaches. However, it’s a useful method to experiment with.
Practical Tips
To reiterate, always use the lowest practical ISO setting to minimize noise and achieve the best image quality. If you need to increase the ISO for a faster shutter speed, don’t be frightened to do so. However, ensure proper exposure and maybe consider ETTR to reduce visible noise.
Utilize noise reduction techniques in the camera and post-processing. A good quality noise reduction program makes a lot of difference.
