Introduction to ISO in Photography

One of the three pillars of photography that can dramatically affect the look of your images is camera ISO (the other two being shutter speed and aperture). Like those two settings, ISO controls the brightness of your photos, and it is a crucial setting to use properly if you want to take the best possible images. In this chapter of Photography Basics article, we will explain ISO using simple language and examples so that you can make the most of it for your own photography.

What is ISO?

In very basic terms, ISO is simply a camera setting that will brighten or darken a photo. As you increase your ISO number, your photos will grow progressively brighter. For that reason, ISO is a good tool to help you capture images in dark environments or be more flexible about your aperture and shutter speed settings.

However, raising your ISO has consequences. A photo taken at too high of an ISO will show a lot of grain, also known as noise, and might not be usable. So, brightening a photo via ISO is always a trade-off. You should only raise your ISO when you are unable to brighten the photo via shutter speed or aperture instead (for example, if using a longer shutter speed would cause your subject to be blurry).

Note how much brighter the image gets when ISO is increased from 100 to 1600

Common ISO Values

Every camera has a different range of ISO values (sometimes called ISO speeds) that you can use. A common set is as follows:

ISO 100 (low ISO)

ISO 200

ISO 400

ISO 800

ISO 1600

ISO 3200

ISO 6400 (high ISO)

Quite simply, when you double your ISO speed, you are doubling the brightness of the photo. So, a photo at ISO 400 will be twice brighter than ISO 200, which will be twice brighter than ISO 100.

What is Base ISO?

The lowest native ISO on your camera is your “base ISO”. This is a very important setting, because it gives you the potential to produce the highest image quality, minimizing the visibility of noise as much as possible. Some older DSLRs and a number of modern cameras, such as the Fuji X-T2 have a base ISO of 200, whereas most modern digital cameras have a base ISO of 100. Optimally, you should always try to stick to the base ISO to get the highest image quality. However, it is not always possible to do so, especially when working in low-light conditions.

Side note:

Some cameras have extended “HI” and “LO” values for ISO that might stretch beyond their native range. However, these are completely simulated and lower your image quality. We recommend avoiding them.

Low vs High ISO Noise Visibility

To give an example of two photos taken at different ISO values, take a look at the comparison below. Pay attention to the level of noise (graininess and blotchy colors) in the images:

The difference is clear – the image at ISO 3200 has much more noise than the one at ISO 200 (which I brightened with a long shutter speed instead). This is why you should avoid high ISOs whenever possible, unless conditions require you to use them.

How to Change ISO

Changing your ISO varies from camera to camera. Here are some common ways to change ISO:

  • To start, enter a mode that lets you select the ISO yourself. Get out of Auto mode, and go to ManualShutter PriorityAperture Priority, or Program (we tend to prefer Aperture Priority or Manual).
  • For entry-level DSLRs and mirrorless cameras, you probably need to open a menu (possibly the “quick menu”) and find the section for ISO. Select the value you want, or set it to Auto.
  • For higher-end cameras, there may be a dedicated “ISO” button on the camera. Press it while spinning one of the wheels to change your ISO setting. If you don’t see a button labeled “ISO”, it is still possible that your camera will let you program one to perform this task.
  • Other cameras may have a dedicated wheel that already has various ISO settings marked. This makes things even easier.

Check your camera manual if you still aren’t sure. However, it is worth being very familiar with how to change your ISO setting quickly, since it’s something you will likely be adjusting quite often, especially if you shoot in low light conditions without a tripod or flash.

What ISO Should You Use?

Many photographers understand the basics of ISO, but they aren’t sure which ISO value to actually pick in the field. In practice, there’s a reason why your camera allows such a wide range of ISO settings: Different situations call for different ISOs. Below, we will cover some of the common scenarios you may come across.

When to Use Low ISO

As discussed above, you should always try to stick to the lowest ISO (base ISO) of your camera, which is typically ISO 100 or 200, whenever you can. If there is plenty of light, you are free to use a low ISO and minimize the appearance of noise as much as possible.

Even in dim or dark environments, you still might be able to use a low ISO. For example, if you have your camera mounted on a tripod or sitting completely still on a table. In that case, you can safely use a low ISO and brighten your photo via a long shutter speed instead, since you won’t introduce camera shake. However, keep in mind that if your camera does use a long shutter speed, anything that is moving will look like a ghost:

Oh No! It’s a GHOST ATTACK!

Just kidding, of course! That’s my lovely nephew being the subject of my long exposure test. I set the camera to the lowest ISO to retain the detail, which required a long shutter speed of five seconds in order to capture a bright enough photo. My nephew sat still, while my friend stepped in for a brief moment to introduce the ghost 🙂

When to Use High ISO

Even though it is ideal to use low ISOs, there will be plenty of times when a high ISO is necessary in order to take a good photo in the first place. The simple reason is that you are often fighting against motion blur, and you will need to pick between a sharp photo at a high ISO, or a blurry photo at a low ISO. Take a look at the image below:

NIKON D700 + 300mm f/4 + 1.4x TC @ 420mm, ISO 800, 1/2000, f/5.6

I captured these Black Skimmers at 1/2000th of a second and ISO 800. Here, my camera needed 1/2000th of a second to fully freeze the birds while they were in flight. What would have happened if I had set ISO 100 on my camera instead? I would have needed a shutter speed of 1/250th of a second to capture a bright photo. At that setting, there would have been a lot of unwanted motion blur in the picture, since the birds were moving so fast. In short, I would have ruined the picture.

The bottom line is that you should increase the ISO when there is not enough light for the camera to capture a sharp, bright photo any other way. When I shoot handheld photos indoors without a flash, I always set my ISO to a higher number to capture the moment without introducing blur. Or, when photographing ultra-fast action like in the bird picture above, raising your ISO is often necessary.

On most cameras, there is a setting for Auto ISO, which works great in low-light environments. The beauty of this setting is that you input the maximum ISO you are willing to use, so that the camera does not cross that limit. Personally, if I want to limit the amount of noise in a photo, I will set my maximum ISO to something like ISO 800, 1600, or 3200. The downside is that the camera will start using progressively longer shutter speeds if it reaches these ISO limits, which leads to more motion blur. Everything is a trade-off!

Minimizing Noise and Maximizing Image Quality

Some photographers think that the best way to capture high-quality images is to use Base ISO 100% of the time. However, as demonstrated above, that simply is not true. Sometimes, you’ll be in dark environments when you have no choice but to use a higher ISO.

You should only use base ISO when there is enough light to do so. Don’t try to force ISO 100 in a dark environment, or your photos will come out way too dark. Similarly, if you’re using a fast shutter speed to capture action, it’s essentially the same as taking pictures in a dark environment (since you strictly limit the amount of time your camera sensor is able to capture light). So, for certain types of sports and action photography, a high ISO might be your only option.

To maximize your image quality, here are the four steps you need to follow:

Select the aperture setting that will provide your desired depth of field.

Set your ISO to its base value, and put your shutter speed to whatever setting provides a proper exposure.

If your subject is blurry, progressively raise your ISO and use a faster shutter speed until motion blur disappears.

If your ISO is getting too high and you still have the ability to use a wider aperture, open it up until the ISO gets to a more manageable level, even if it means sacrificing some of your desired depth of field.

That’s all it takes! If you follow these steps, you’ll capture the maximum image quality each time. You’ll find the ideal balance between noise, motion blur, and depth of field.

Common ISO Myths and Misconceptions

ISO has a lot of myths surrounding it, including some that are quite common to hear. In this section, we will quickly address some of those concerns so that you are not misled about this topic in the future.

Is ISO “Sensor Sensitivity”?

This is the most common myth related to ISO. It is something you will see all over the web (and in print). However, although it may help you to think of ISO as “acting like” camera sensor sensitivity, that’s not what it actually does. Instead, digital sensors only have a single sensitivity, regardless of your ISO. It is more accurate to say that ISO is like a mapping to tell your camera how bright the output photo should be, given a particular input exposure.

Is ISO Part of Exposure?

No, ISO is not part of exposure. Shutter Speed and Aperture brighten your photo by physically capturing more light. ISO doesn’t do that; instead, it essentially brightens the photo you already captured. So, photographers don’t consider it to be a component of exposure.

Is Raising ISO Just Like Brightening Your Photo on a Computer?

This is a clever question, but, again, it is simply a misconception. Brightening a photo on your computer can act in many ways like raising your ISO, since it does make noise more visible (and it leads to a brighter image). But the simple difference is that raising your ISO in the camera nearly always provides better image quality than brightening a photo on your computer. In other words, it is better to use ISO 800 when necessary, rather than brightening an ISO 100 photo to a huge degree in post-processing software like Lightroom!