Understanding ISO for beginners in photography.

ISO is one of the fundamentals of photography. Yet, it is probably one of the most misunderstood terms in the world of photography.

The truth is, its meaning varies depending on the context and even the era it is being used.

It works hand in hand with aperture and shutter speed but it doesn’t handle light the same way.

Knowing exactly how ISO works will help you capture images with better quality and avoid beginner mistakes and misconception. 

Is ISO an acronym?

The International Organization of Standardization develops various globally accepted standards. This may come in the form of systems, products, measurements and the one the interest us, film speed standards.

However, it is not an acronym for their organization. I mean, the words themselves translates to IOS right?

It is derived from the word “isos” which means equal. They use it for branding purposes so their name remains the same whatever language or country you are in.

But this bit of knowledge is more like a “nice to know” thing.

The name of the organization itself has little to do with how it works on your camera.

What is ISO?

In film cameras, ISO is a standard system that measures the film’s sensitivity to light. This system was later adopted by digital cameras.

In digital photography, ISO simulates film’s sensitivity but it is not the digital sensor’s sensitivity to light. Instead, it measures the applied “gain” or amplification to the light you have gathered.

It allows you to change the brightness or darkness of your image. But films and sensors apply output brightness in a different way. More on this in the next section.

Anyway, when you push the ISO button, you’ll see numbers like 100, 200, 400, 800, etc.

These numbers will help you quantify the amount of brightening you are applying.

Set of images showing how ISO affects the brightness output.

The higher the ISO setting, the brighter the image gets.

Whenever you double the value, you also double the brightening applied in your image.

How ISO Brightens Your Images:

To better explain it, let’s go back to the era of film cameras.

Before the digital revolution, photographers use films to capture images. These films are labeled with either “ASA or DIN ratings”. Both are ratings to the film’s sensitivity to light. And both systems were later unified to ISO.

A high ASA/DIN rating means the film will be very sensitive to light. This allows you to use faster shutter speed and smaller aperture so you can shoot in low light situations.

But you can’t actually change it on the fly the same way a digital camera does. And this is where the confusion comes in.

Film from a Kodak camera.
Image Credit: Melissa Gagnon

Camera sensor sensitivity does not change just like films do. Normally, a camera’s true ISO sensitivity rating is or close to the base ISO.

It is, however, capable of changing the light output brightness of your gathered light by pumping electricity to the sensor.

This effectively “maps” the light you’ve gathered from shutter speed and aperture and converts it to digital data. This data will then be used to write files in your camera’s memory card.

The existence of digital conversions is one of the key differences that makes it behave differently from film cameras.

I gotta admit. It is intuitive to think of it as sensitivity even for digital cameras which is why a lot of resources defines ISO as such.

Here’s a question. Since my sensor is more “sensitive” to light, I can gather a brighter image to reach proper exposure even with less light, right?

Unfortunately, it isn’t as straightforward as that because…

ISO is Not Part of Exposure:

Unlike aperture and shutter speed, ISO does not physically increase or decrease the amount of light gathered.

Therefore, it is not part of the “light gathering process” or exposure.

Think of it as the volume knob on an FM radio. You can increase its volume as much as you like but if the signal is weak, you’re only going to increase the sound of static noises.

In your camera’s case, the only way to increase that signal is through aperture or shutter speed.

The next time you take a photo, try to get as much as possible light through aperture and shutter speed first before increasing your ISO setting.


Because it affects more than just the brightness of your image…

How Low vs High ISO Settings Affects Your Photos:

Aside from the brightness, ISO also affects the amount of image noise, dynamic range and color accuracy of your images.

It is kind of a drawback for increasing the light output of your exposure.

Image Noise:

The biggest and most noticeable drawback when using high ISO is the amount of image noise.

Image noises are splotches or speckled particles that appear randomly on your photo. Higher ISO values are prone to more noise.

ISO 200 vs 6400 noise comparison.

As you can tell at the image above, setting at 200 looks much cleaner than 6400.

The best practice is to always try to keep your ISO as low as possible if you can.

But don’t just use low value for the sake of it because image noise can appear even at low ISO if your light is lacking.

Remember the signal thingy I’ve mentioned earlier? Get as much light as you can through shutter speed and f-stop settings.

If needed, don’t be afraid to raise ISO. If you gathered a pretty good amount of light, then raising it will not generate too much noise. You’ll get cleaner images getting the correct exposure in-camera than in post-production.

Color Accuracy:

Color accuracy the camera’s capability to show true color representation. Meaning, white should look white, not yellowish or some other color.

Using extremely high ISO can cause a color shift to your image.

ISO 200 vs 12800 color accuracy comparison.

The image I’ve provided above might not be the best example since I’ve got plenty of light coming from the sun.

If you are shooting in low-light this issue might look more severe.

Fortunately, this can easily be fixed through the color temperature slider of Photoshop/Lightroom.

Dynamic Range:

Cameras can only record a finite amount of information even shooting at RAW. Dynamic range is your camera’s capability to record the darkest and brightest tone in your image.

Same as the other two, high ISO tends to reduce the dynamic range depending on your camera’s sensor capability.

Cameras with low native ISO usually has better dynamic range performance.

This dynamic range test video from Dave Morrow is probably the best resource for this topic.

This piece of information can be useful for high dynamic range images, night photography or certain landscape shots.

Personally, I do not mind adding a few steps in my post-processing workflow.

So if I absolutely need to capture a high dynamic range image, I just use auto bracketing and apply exposure stacking in post-production.

Don’t stress out too much in this aspect if you’re just starting out. If you’re constantly checking for image noise, you’ll also take care of this issue in the process by supplying more light to your sensor.

How to change the ISO settings:

The ways to change ISO differ from camera to camera.

You cannot change it when you are in the auto exposure mode. So first, you gotta make sure that you are either on the Manual, shutter priority, aperture priority or Program shooting mode.

Most higher end consumer cameras have a dedicated ISO button usually found at the top along with the dials.

ISO button on Canon 7d

All you need is to press that button then select your desired setting by moving the rear dial left or right.

For entry-level DSLRs or Mirrorless cameras, you may have to go over the camera menu at the back to find the setting.

Some retro style cameras like the Fuji lineup have a dedicated dial with different ISO settings already marked. So all you have to do is move the dial to your desired value.

For all of them, you should also see an option to set it to auto ISO.

ISO Ranges:

ISO ranges differ depending on your digital camera’s model. Let’s take the Canon 7D for example. This camera has a standard ISO from 200 to 6400.

When enabled, you can extend the range from 6400 to 12,800.

Example of ISO ranges on Canon 7D.

However, I will suggest that you avoid using extended ISO, especially on the high end.

Here’s why…

Base, Amplified and Simulated ISO:

How your camera deals with different ISO ratings is what separates digital cameras from film cameras.

For film cameras, you have to change the film roll to change the ISO (ASA/DIN film rating). With digital cameras, you can change it on the fly with just a few steps. 

Digital cameras achieve this by adding voltage or applying software processing.

We can categorize them into 3 things:

  • Base/Native ISO:

    Base ISO is usually the lowest standard setting in your camera. But, it varies depending on your specific camera model.

    This is the setting a certain camera sensor is designed for. Theoretically, your camera will generate the least amount of noise, and the best dynamic range and color fidelity in this setting.


    Because in this setting, the camera uses the least amount of voltage(or none at all) to map out your current ISO settings. You can say that it is the optimal ISO value for your camera.

    A word of caution though: Lighting changes all the time, especially when shooting outdoors.

    We shouldn’t blindly use the base ISO for all our shots. We don’t want to end up with underexposed images that we can’t even save it in post.

  • Amplified ISO:

    These are the ISO ranges where analog amplification is applied. In other words, a certain increase in voltage is applied to the sensor in this range.

    The noise almost always starts to show up on both amplified or simulated ISO. But the noise levels on amplified ISO is less severe than using simulated ISO.

    Actually, it’s perfectly okay to use it. The best practice is to use the native ISO whenever you can but don’t hesitate to bump up your gain if needed.

  • Simulated ISO:

    In this range, your camera uses digital processing to simulate higher ISO values.

    For example, you used an extended value of 12,800. You’ll see that your image is brightened. But your camera actually used ISO 6400 and applied digital processing.

    It is pretty much the same as raising the exposure in software like Photoshop or Lightroom.

    Why do you need to know that?

    In most cases, you will get cleaner images using the standard ISO (Native and Amplified) than using the extended ones.

    I would suggest avoiding these ranges altogether. Except perhaps, the lower end values like 50 or 100 (depending on your camera model).

When to use a low ISO setting:

Ideally, you would want to use your camera’s base ISO as much as you can.

And if your image is underexposed, try to see if you can still get more light through f-stop or shutter speed first before raising your gain settings.

Make the decision based on the depth of field or motion blur you want out of your image.

You can also use gears like tripods, monopods, flash, and reflectors. This will give you more leeway when balancing your exposure.

But of course, if the situation requires it, do not hesitate to raise your ISO setting.

As mentioned earlier, it is better to increase ISO in-camera than in post-production. And don’t forget to avoid the higher end values of your extended ISO.

When to use a high ISO setting:

Not all shooting conditions will be favorable for you. There are times when you really need to bump up your gain…

Here are some scenarios:

Reducing Motion Blur and Freezing the Motion:

Hummingbird shot at high ISO and fast shutter speed

You should have fast enough exposure time to capture a fast-moving object Otherwise, you’ll only get an image with a lot of motion blur.

This is typical when you are shooting birds in flight, car races or any sports.

Because of this, you will have very little light to work with, resulting in dark images. You may be able to use a wider aperture but it will be harder to nail your focus. In this scenario, your only option is to increase your ISO.

Photographing the night sky:

These include photographing the moon, city lights or stars.

You will be working on extremely low light conditions so most of the time, you may be forced to use high ISO.

You might be tempted to just use your tripod and set your camera at long shutter speed. But, you need to be aware that our planet is constantly moving whether you notice it or not.

At worst, you might get a blurry subject due to the earth’s movement. And while it’s not so bad to use long exposure time, you will get a different kind of photo as a result.

Using long lenses without stabilization:

This has a lot to do with your shutter speed and camera shake. The longer the lens, the faster shutter speed is required to cut camera shake. Needless to say, camera shake can cause blurred images.

Unfortunately, if you do not have any sort of stabilization, you will have to use faster shutter speed. You can follow the reciprocal rule and use enough shutter speed to reduce camera shake blur.

In return, this will also darken your image so you’ll have to increase ISO to compensate for that.


ISO can affect quite a lot of factors in your image. Understanding these effects and how it works is crucial for maximum image quality.

Best to avoid extended ISO ranges and don’t just use the base gain for all your shots. There are times that you will be needing high ISO as well. Changing the gain in-camera works better than changing it through photoshop or some other image software.

Hope this article helped you gain confidence in handling your camera. If it did, consider subscribing  to our list get notified whenever we publish posts like this.


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