What is ISO in Photography? [Beginners Guide]

As a beginner, ISO is one of the core concepts you need to understand in photography. It’s one of the crucial settings that affect exposure.

And like aperture and shutter speed, it doesn’t just affect the brightness of your image. It can also influence a lot of other factors in your photos.

It does sound like jargon, but its concept isn’t tough to grasp. Buckle up cause we’re about to learn how ISO works, its effects on your image, and some of the best practices when taking photos.

What is ISO in Photography?

What is ISO in Photography?

What is ISO in Digital Photography?

In digital photography, ISO or “gain” is an applied amplification to the light you have gathered.

Before digital cameras, photographers used films to capture images. These films are labeled with “ASA ratings,” which is the sensitivity of the film to the light.

A high ASA rating means the film will be susceptible to light. This allows you to use faster shutter speed, smaller aperture, or shoot in low light situations.

What is ISO in Digital Photography?

What is ISO in Digital Photography?

Digital cameras don’t use films.

Instead, your camera pumps more electricity to the sensor. This is then converted to digital data that will be used to write files in your camera’s memory card.

The existence of digital conversions is one of the key differences, which makes it behave a little differently from film cameras.

In that sense, “ISO in digital cameras is the simulation of the ASA ratings in films” might be a better description.

How to change the ISO settings:

Depending on your camera, you can this setting pressing the “ISO” button then dialing it up or down.

How to change the ISO settings

How to change the ISO settings

On most consumer cameras, this button is usually found at the top along with the dials.

There is also an option in your camera to set it on Auto ISO mode. You let the camera decide what it thinks the proper ISO settings for your scene.

It’s like aperture or shutter priority mode except that you can use this even if you are in Manual mode.

If you’re just starting, I suggest learning how to shoot in a full manual mode. Ditch the auto settings until you have a better grasp of how your camera works.

This way, you can shoot in any light situations. And of course, this gives you more creative freedom when composing your images.

That said, though, most modern-day camera models are pretty good at guessing the proper exposure settings. You can probably get away with it most of the time. Provided you are shooting in standard lighting.

Stops and Increments:

“Stops” is a term used to quantify each increment in your exposure settings.

Whenever you double the value of your ISO, you are exposing the image one stop higher.

For example, ISO 200 is one stop higher than 100, and 400 is one stop higher than 200, while 400 is two stops higher than 100.

Stops and Increments

Stops and Increments

In your camera, there is a setting whether you want to set each increment to 1/3 of a stop, 1/2, or 1 full stop.

How Digital ISO works:

Like shutter speed and aperture, you can use ISO to control the brightness of your photo. But unlike both, it does not change the actual amount of light you have captured.

It gives you the illusion that you are gathering more light. But in reality, you are boosting the light you have gathered.

Whenever you change your ISO, your camera kind of “maps” the light signal received by your sensor. It outputs the brightness levels depending on your ISO settings.

This affects the brightness and the amount of noise in your image. Higher ISO means a brighter image but more sound.

To explain it further, we’ll need to get a little geeky…

The light’s first point of contact is with your lens. This is where aperture kicks in. It controls the amount of light that passes through the lens.

The light that goes through the lens is then regulated depending on how long your camera’s shutter remains open. This is the exposure time or shutter speed.

At this point, the light accumulation is complete, and the camera sensor will read the light.

​​​​These light signals will then be “mapped,” depending on your ISO settings. This “mapping” is achieved by pumping voltage into the sensor to reflect your current gain setting.

Lastly, these analog signals will be converted to digital data. This digital data will be used to write the images to your memory card.

To simplify this, let us use an analogy…

The microphone analogy:

Think of ISO as a microphone. Except that you can’t turn off the sound completely.

You can amplify the music that is heard by turning the volume up or down.

A barely audible voice can still be amplified to acceptable levels by raising the volume.

Similarly, you can turn the volume down for that loud buddy of yours so it won’t be heard by your neighbors three blocks away.

Either way, you can control the loudness by turning up the volume up or down.

In photography, the sound intensity is the light accumulated from the aperture and shutter speed. And the volume control would be the ISO.

How ISO affects Brightness and Image Noise:

You can brighten your image by increasing your ISO. The higher the gain setting, the brighter the image.

How ISO affects Brightness and Image Noise

How ISO affects Brightness and Image Noise

But, it is not without a drawback. ISO also affects image noise.

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

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

Arguably, it can sometimes have a good effect on your image, like giving it texture or “style.”

But most of the time, it leaves undesirable effects that can distort, soften, or even destroy an otherwise good shot. This is the reason why most photographers try to reduce noise as much as they can.

How ISO Affects the Dynamic Range and Color Accuracy:

Digital cameras aren’t as powerful as our eyes and can only record a finite amount of information. Dynamic range is your camera’s capability to record the darkest and brightest tone in your image.

Admittedly, the loss in dynamic range and color accuracy isn’t that huge for most shooting situations. For most cameras, it is not noticeable at all unless you go at extremely high ISO.

This knowledge is pretty helpful if you plan to shoot a lot of night photography, though.

Higher ISO values lessen the dynamic range of your image.

With that said, some part in your highlights or shadows will be “clipped” if you exceed your camera’s dynamic range. And there’s no getting back the details once a part of your image is clipped.

And yes, even Photoshop can’t save you from it.

How ISO Affects the Dynamic Range and Color Accuracy

How ISO Affects the Dynamic Range and Color Accuracy

Of course, you can compensate by adjusting your shutter speed or aperture. But for many situations, you will continuously have a dilemma on which part of the image you want to save.

Whether you choose to save the highlight or the shadow is entirely up to you. It should be based on the story you want to tell.

Color accuracy may also suffer when you use extremely high ISO value. This is the camera’s capability to show accurate color representation.

For example, a white wall should appear pure white. Not something yellowish or cream color.

Theoretically speaking, using anything other than the base ISO can impact the dynamic range and color accuracy.

But by how much?

First off, it varies depending on your camera’s sensor capability and the available light in your scene. Generally speaking, the difference isn’t too high, even for entry-level cameras.

As long as you don’t go crazy high with your ISO settings, you should be fine.

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 use bracketing and apply exposure stacking in post-production.

For every other shot, I just decide which parts of the image I can’t afford to lose.

I tend to always save the highlights, so usually, I end up with an underexposed image, which is fine since I can still adjust it during post-processing.

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.

And if you fiddle in the camera’s menu, you can extend the ISO, giving it more options. When enabled, you can now select ISO from 100 to 12,800.

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 to adjust the ISO (ASA film rating). With digital cameras, you can change your ISO on the fly with a click of a button.

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

We can categorize them into three things:

– Base/Native ISO

This is the setting a specific camera sensor is designed for.

Theoretically, your camera will generate the least amount of noise and the best dynamic range 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.

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

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

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

– Amplified ISO

These are the ISO ranges where analog amplification is applied. An inevitable increase in voltage is applied to the sensor when using ISO 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.

It’s perfectly okay to use it. The best practice is to use the native ISO whenever possible, 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 ISO value of 12,800. You’ll see that your image is brightened. But your camera 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 ISO.

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

Best practices when adjusting your ISO settings:

As a beginner, it is good to remember that a higher ISO value produces noisier photos.

Noise is always there whether you notice it or not. And remember, ISO only amplifies the natural light you have gathered. So the more you amplify, the more you see the noise in your image.

If you have very little light, to begin with, you’ll have an image with a lot of noise. Try opening bigger aperture or slowing down your shutter speed first before increasing your ISO.

Gathering more light signals means less amplification is required to get proper exposure. And less amplification will render a cleaner image.

Let’s go back to the microphone analogy. You can amplify the sound of your voice by turning up the volume.

But if your voice is faint, you will need to amplify the volume high enough to make the sound understandable.

By doing this, you are also amplifying everything else. This will also amplify the background noises and electrical static noises of your microphone.

If you go too far, you know it won’t be a pleasant experience, don’t you?

So why not speak a little louder so you won’t have to turn up the volume too much? Stop being shy and sing your heart out!

Kidding aside, it is a good practice to use the lowest ISO whenever you can.


While it is a good practice to keep it low, the base ISO is not always the best. You will get a cleaner image using higher ISO in-camera than by doing it in post-production.

So if you need to bump up your ISO to get the proper exposure, by all means, bump it up.

Get the right exposure in-camera. You should be fine as long as you keep your ISO at the native and amplified ISO range.

When to use a low ISO setting:

As a rule of thumb, always try to use the lowest possible ISO value. Always try to see if you can increase your aperture or shutter speed settings first if you lack light.

You can use gears like tripods, monopods, flash, and reflectors, to gather more light.

Ideally, you would want to use your camera’s base ISO. But of course, if the situation requires it, do not hesitate to increase ISO.

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.

BUT, (yes, there’s always a but) there are some scenarios where you have no choice but to increase the ISO.

When to use a high ISO setting:

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

Here are some scenarios:

Reducing Motion Blur and Freezing the Motion:

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.

Reducing Motion Blur and Freezing the Motion

Reducing Motion Blur and Freezing the Motion

Photographing the night sky:

These include photographing the moon, city lights, or stars.

These types of shots are pretty hard to capture if you’re a beginner. That’s because you will be working on shallow light conditions.

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 continuously 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.

Photographing the night sky

Photographing the night sky

Shot at using just enough shutter speed. And compensating with higher ISO.

Shot a plodding shutter speed.

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.

Camera shake can cause blurred images.

To avoid this, you can follow the reciprocal rule and use enough shutter speed to reduce motion blur. Unfortunately, this will also darken your image, so you’ll have to increase ISO to compensate for that.

How to deal with noise in post-production:

As mentioned earlier, image noise isn’t always bad for your image. Too much noise is.

Learning how to make noise reduction is almost always a must if you want a high-quality image.

When dealing with noise in post-production, there are two types to look for:

Luminance Noise:

These are colorless noise that appears randomly in your image. It looks like the noise that you’ll typically get from film cameras. They are called grain in the film days.

They do not look too distracting unless there’s too much of them.

Color Noise:

These are little multi-colored splotches found in your image.

This type of image noise looks terrible. They scream for attention and can ruin your photo.

Generally, you want to avoid color noise at all costs. But having a slight amount of luminance noise is not so bad for your image.

Just keep in mind that excessive amounts can reduce the sharpness of your image.

We’ll be creating a step by step guide on how to make noise reduction. For now, just remember that digital cameras are prone to digital noise at higher ISO.

Five key things to remember about ISO:

  • ISO can help you brighten the image you are trying to capture.
  • But don’t overdo it, or your image will look noisy as hell. Using high gain value can also reduce the dynamic range and color accuracy of your image. Consider adjusting your aperture and shutter speed first.
  • Don’t force it – It is always recommended to use your camera’s base ISO, but there are times when you have to use higher settings.
  • Avoid using the higher end values of your extended ISO. Try to identify which settings are simulated ISO for maximum image quality.
  • Adjusting ISO in-camera can yield cleaner images than brightening in post. So don’t be afraid to increase it when needed.


ISO can affect quite a lot of factors in your image. Understanding its 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 need high ISO as well. You are changing the gain in-camera works better than changing it through photoshop or some other image software.

I hope this article helped you gain confidence in handling your camera. If it did, how about sharing this post with your photography buddies?

Also, don’t forget to get notified about our latest excellent posts!