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ISO settings: What is it, how to use & what does it do

Shubham Davey 0
Reading Time: 14 minutes

Exposing a scene properly is a crucial thing you should do in order to take great photos. ISO settings are one of those three pillars that play an important part in composing a rightly exposed image. However, it is important to use all three to capture that perfect shot, the way it looks to your eyes.

Considering the fact that some of the most beautiful photos are taken in night light. Be it the galaxy view, or the aurora light, or simply a star trail – you name it. Night photography takes a huge part of photography on the whole. Having said that, how do I mention ISO sensitivity playing a huge part in taking clear and noise-free images in night light. I’m sure you are curious & eager to know more about ISO settings, but let’s take it slow and easy. This post is for those who are new to this space and curious to know & learn more about this.

In this post, I will explain the following questions to help you master ISO settings:

  • What is ISO sensitivity & what does it do?
  • How do ISO settings affect your pictures?
  • What is high ISO & Low ISO?
  • Advantages & Disadvantages of high ISO
  • Why & When use high ISO?
  • What ISO settings are ideal? Recommended ISO settings

Are you ready for answers to these questions?

Let’s begin¬†ūüėČ

What is ISO sensitivity

ISO settings

ISO is an acronym for International Standards Organization. A perfect blend of ISO settings along with Aperture and Shutter speed makes a better-composed scene that you can capture it. Each value of ISO settings determines a certain light sensitivity of that scene. ISO settings ranges from 100 to 6400 and beyond, depending on the DSLR you own. Technically, ISO is just the light sensitivity of your DSLR camera. High ISO means high sensitivity and low ISO means low sensitivity. Furthermore, the sensitivity is how reactive the image sensor is to the incoming light.

High ISO vs Low ISO is a big confusion among beginners and to sum the who story of it in one line, it would be something like this:

Lower the ISO settings means your image sensor is less sensitive to the light. And higher the light sensitivity, more digital noise it creates.

Technically, a higher sensitivity to light will enable you DSLR to work better in low light situations but also invite digital noise in your photographs. To take better-lit photos in night light without digital noise? That’s what this post is all about.

How is ISO measured?

ISO is measured as the percentage of brightness or exposure of a particular scene to the image sensor. It’s visually 18% grey hence it’s not visible to the human eye, but the camera software can make out the difference. This doesn’t mean that all the ISO values correspond to fixed brightness levels, it doesn’t work that way. It’s constant 18% whichever ISO mark you operate on.

Consider these settings to better understand ISO measurement concept:

ISO setting: 100

Shutter speed: 1 second,

Aperture: f/1.0 correspond to the fixed brightness “EV 0”.

However, that same brightness level could also be achieved at

ISO setting: 200

Shutter speed: 1/2 second,

Aperture: f/1.0

ISO 400

Shutter speed: 1/4 second,

Aperture: f/1.0

The point is, to take a perfect image, you should keep the balance of the three elements of the exposure triangle. That is, if you go down one stop in shutter speed, increase the ISO by one stop, if you go two stops down in shutter speed, go one stop up in ISO. You see the balance is maintained well, less light getting in more the image sensor becomes sensitive to the image. At a lesser light, the sensitivity remains effective. This way no matter what ISO you operate on you will arrive at the same final EV brightness of 18% grey.

What do ISO settings do to your images?

The ‘What does it do’ part of this question is explainable by an example. Consider you are shooting an indoor marriage scene. The light is bright, there’s a lot of things happening in the scene. You cannot afford to miss any scene as it’s not doable again. What is the best thing to do in this case? Shutter speed around 1/60th to 1/100th of a second, depending on the distance between you and your subject the aperture is a variable.

What about ISO? Indoor, under bright light, the lowest ISO will do. Reason? The light is already bright, you don’t want to let the image sensor react more to the incoming light. Do you? This is the reason lower ISO levels of 50 and even 25 are only in high-end DSLR cameras. The image sensors in such DSLRs(like the canon 5DS R) are capable of shooting on extended ISOs¬†and this makes a huge difference in terms of image quality and the digital noise.

All that the extended ISO do is capture same information of the scene at a comparatively lower digital disturbance. For those who are taking pictures for facebook or Instagram might not find this useful, but for those who are specific for the quality will find it useful for the images with very less noise/disturbance.

How do ISO settings affect a picture

If not completely, you now have a gist of ISO settings and why not, I’ve just scratched the surface. To better understand, why high ISO in the night light is not good, I will explain what happens when you shoot in night light at comparatively high ISO.

It’s not that, low ISO settings do not have digital noise, but the digital noise is much smoother. It doesn’t make it obvious that its present. On the other hand, at high ISO, the grains of noise is so rough that it turns out as if there are pores in the photo itself. It’s that unpleasant to watch. At high ISO, the image sensor works hard to take most of the light and make the photo lit properly. That is the image sensor becomes more sensitive to light and hence the ‘noise’ or the pores turn out to be so rough.

Furthermore, it doesn’t always happen in night light. Digital noise can disturb your photos in daylight also. When you have a darker background or a contrast color background wrt to the subject or your scene. This way it turns out very obvious of its presence.

ISO settings

What is Digital Noise?

It’s any light signal that is not originating from the object in the scene and hence making a rough appearance of random colored lights.

The image sensor is designed to bring out the best from the scene at low ISO, which in most cases is ISO 100. And some high-end DSLRs even have ISO as low as 25, which produce little to no digital noise or grains in the image.

To make it simpler all I can say is ISO affect pictures by changing shutter speed and aperture according to the ISO you have selected. Irrespective of the camera mode, the ISO is independent of it. While you work on High ISO will let you work at higher shutter speed and/or lower aperture. Another way ISO affects your photographs is with colors.


Depending on the white balance mode you are operating in, the light sensitivity will change the color of the actual image. It will give unpleasant look in the images.

Taking photos under bright light at high ISO and at slower shutter will give you over-exposed images. Reason being the high ISO (light sensitivity) slow shutter speed(allowing more light) and the bright light. The bright light and slow shutter speed itself are enough to over-expose an image, to make it worse, you have a high ISO.

Should you leave your ISO settings in ‘Auto mode’?

For newbies, who are taking baby steps in this space, I would recommend using ‘auto mode’ for now. While you experiment by shooting more, failing, experiment even more and fail better, you will get a good hold of the ISO settings and even master it. No doubt, the auto mode reduces time to set it according to the scene; but it also takes the liberty to experiment and take better photos.

Once you are ready to get out of your comfort zone and take control of the ISO sensitivity, you can analyze the scene and decide to go for a certain ISO. Before you know more about this, you should know how the image quality gets affected with increasing ISO settings.

With increasing ISO settings you will:

  1. Have to compromise the fine details in the image
  2. If you enlarge the image for canvas prints or even zoom in, you will find a lot of disturbing noise in the darker portion of the image.

Having said this, you will find a doubt inside you which is,

How to determine best ISO settings for shooting perfect photos

While determining the ISO, I depend on 3 factors:

  • Light
  • Tripod
  • Motion

If the subject is properly lit, the DSLR is on a steady tripod, and the subject isn’t moving much, then a lower ISO is fine. Alternatively, if the subject is in dark or low light, I don’t have a tripod, and my subject is moving a lot, I’d go for higher ISO.

The take here is, that I get to work at faster shutter speed and still get a perfectly lit shot. In case I have a tripod, I can bring the ISO settings to a mid-range depending on the light. A steady tripod will reduce a lot of noise.

Either way, the final image will have a lot of noise. But some shots look beautiful with those grains. For example, the galaxy shot, or a starry night. These noise grains will add the beauty to such images.

Advantage & Disadvantages of various ISO sensitivity levels

If you’ve made this far, you must be curiously searching for perfect ISO settings for conditions you mostly work in. This brings down the question to the fact that you are not in same lighting conditions all the time. Hence there is nothing called perfect ISO settings for all conditions, you can average out the ISO settings. You have to determine it every time you shoot.

Here’s a brief guide that will be helpful for various conditions. What you will find below is ISO to lighting conditions grading and not the otherwise:

Low ISO levels(100-400)


The best-known advantage of using low ISO setting is that you can have smooth, clear and high-quality pictures. The pictures that you take at lower ISO produce better images and comparatively viewable images. The less sensitive your light sensor turn towards light more enhanced the images are produced. Even if you zoom those images, you will not find any grains for the great extent of zoom levels.


Though low ISO gives better picture quality and little to no noise in the images. But the low ISO it has its own problems. Low ISO in low lit conditions does not work well without a tripod. At lower ISO levels, the shutter speed is slower (higher shutter speed) and hence there are high chances that your DSLR may shake and take blurry images.

Furthermore, the lower ISO will limit the wider aperture allowing more light to enter. This again adds on to blurring off the moving objects.

Ideal for: Indoor, better lit, and stationary subjects. If the lighting conditions are fine and you do not have the tripod (which you don’t need in better lit conditions) you can use low ISO settings.

ISO settings
                    ISO: 100, Shutter Speed: 1/30 Aperture: F4.5, Shot on Nikon D3200 by © Shubham Davey

Medium ISO Levels (400-1600)


Medium ISO levels help you get hold of faster shutter speeds and narrower aperture. The results are visibly the same but when it comes to the photo quality for reproduction, medium ISO levels do much better than low ISO levels.

ISO settings
                     ISO: 400, Shutter Speed: 1/30 Aperture: F4.5, Shot on Nikon D3200 by © Shubham Davey


Unlike low ISO, medium level ISO do not produce blurry images unless the light conditions are very poor. Instead, the medium ISO levels tend to saturate colors making it inaccurate. Again, the colors are inaccurate depending on the light conditions. You have to figure out with trial and error method, take photos and see which ISO level gives the best output.

High ISO levels(1600 and beyond)


With high ISO sensitivity, you can operate your DSLR without a tripod in a low light condition. At high ISO, the shutter speed is fast enough to freeze the subject and capture just right amount of light. High ISO comes handy to add HDR effect(to some extent) and mood in black and white images.

ISO settings
ISO: 1600 Shutter Speed: 1/250, Captured in Nikon D3200 by © Shubham Davey

ISO settingsISO: 1600, Shutter Speed: 1/80, Aperture: F4.5. Captured on NIKON D3200 by © Shubham Davey


As you can see in the two example above, high ISO helped me capture the beautiful cake without any shakes (no blur of the flames too)

On the other hand, the macro shot I took to work at faster shutter speed produced a grainy image. It was a windy day, so to capture a perfect shot without a tripod, I had to go for a high ISO.

Recommended ISO Settings

When it comes to working on ISO, it becomes very crucial to understand when and where to use. Ideally, ISO is light dependent and motion of the subject. If your subject is in too bright lighting condition and is not moving much, then the lowest ISO would do.

If the subject is moving a lot and the light condition good then a medium ISO level would do. Furthermore, if the subject is moving a lot and the lighting condition is not that good then a high ISO level is needed. But again, you will have to compromise with the digital noise. It’s an inevitable thing.

High ISO is only useful when you have an immobile subject and poor lighting conditions and you do not have a tripod. Hence a high ISO will do the work for you without a tripod. Other than that, lower ISO will do.

Final thoughts on ISO sensitivity

The image sensor is the most important element in a DSLR. Understanding how it works it will help you take better photos. You would gradually find it easier to get ahead with switching to different ISO settings for different lighting conditions.

Furthermore, you should always keep the basics of ISO in mind. Higher ISO will make the image sensor more reactive to the incoming light. And hence the image sensor will process more light hampering the image for good or bad. High ISO is handy when you don’t have a tripod to keep the DSLR steady. On the other hand, a low ISO will always be helpful.

One thing to keep in mind is that a higher ISO is useful 2-3 out of 10 times. And those times are only when you have to shoot a low light subject without a tripod but noise is unavoidable. Noise is not always painful if you know how to beautify it.

Over to you. What comes to your mind when you¬†hear the word “low light”? How do you tackle it? You up the shutter speed or the ISO? Or both? Let me know in the comment section below. I know I have a lot of information in this post, should you have any doubts, let me know about that in the comment section.

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