ISO in photography

ISO In Photography and How to Use it

Is your camera able to produce good shots even when there is barely any light? Do you understand the role of ISO in photography and how it effects your images?

We are here to help!

What is ISO?

In short, ISO is your cameras sensitivity to light. In particular it is the sensitivity of your cameras digital sensor.

Changing the ISO of  your camera can have a dramatic effect on the look of your photo. Along with shutter speed and aperture the three make up an exposure triangle.  

A standardised set of numbers is used as a scale, like 100, 200 & 400. The lower the number, the less sensitive your film, or digital camera is to light.

In the days of film, you would need to change your roll of film to use a different ISO. With digital cameras we have the distinct advantage of being able to control the ISO of our photos from shot to shot.

As the ISO number doubles, so too does the amount of light being recorded by the camera’s sensor. ISO 400 is twice as sensitive as ISO 200. Just like with shutter speed and aperture, when we double the light to the sensor, we refer to this as one ‘stop’ of light. ISO 400 is one stop brighter than ISO 200.

Imagine we are shooting an image and use the same aperture from shot to shot. For every stop we increase ISO, we can halve the shutter speed that’s required to get the same overall exposure. So in a sense increasing the ISO can allow you to make the shutter close faster. This will produce a sharper image.

You see how all three work in sync in the exposure triangle?

exposure triangle

ISO Noise

If you’ve read the articles about shutter speed and aperture you’ll know there’s always a trade-off to be made when trying to get more light into your camera.

With aperture you get a shallower depth of field as you open up the aperture to let in more light. With shutter speed, as your exposure time increases to let in more light, it becomes harder to get sharp images of moving objects.

There is also a tradeoff for ISO. As you increase the camera’s sensitivity to light, your images get ‘noisier’, sometimes described as ‘grainier’. At the lower values (100-800) the noise is usually impossible to see with your eyes. As you increase the ISO though, you will slowly see more and more noise. Whilst the ISO numbers are standardised, the amount of noise that corresponds to them is not. This means that different cameras produce different amounts of noise at different ISO settings. There are several reasons for this and it is usually the reason one camera body is more expensive than another.

If you compare a point and shoot camera to a DSLR they will display different amounts of noise in their images. This is the case even if the exposures are set on exactly the same settings.

Here are a couple of extreme examples to show you some visible noise.

understanding ISO
ISO in photography

What ISO should I set?

Think about the light available.

Bright lighting, like outdoors in the sunshine, will require a lower ISO. This will of course give a cleaner image with less noise.

Poor lighting, like in a forest under cloudy skies, would require a higher ISO and typically result in noisier images.  

Don’t forget you can always use a tripod though if you want to maintain a low ISO. This will keep your photos noise free. Using a tripod allows you to use a longer shutter speed. This will get precious light to your sensor, rather than having a more sensitive ISO setting. 

We often think of using high ISOs in dark places. However as long as your subject is static, there’s no reason why you can’t shoot at ISO 100 in the dark. So long as you have a tripod.

sunset photography

Love shooting sunsets? Check out this article and use your new ISO knowledge.

Shooting a fast moving subject? We have teamed up with BAPH to bring you more ISO insights.

Where is my ISO setting and how do I use it?

Your ISO setting is a key ingredient of your exposure so it’s displayed prominently on all cameras. On a DSLR you’ll typically find it in the LCD on the top right-hand side of the camera. It will also be displayed beneath the image within the viewfinder. If you are using a point and shoot camera, or a DSLR with liveview, then the aperture setting will usually be displayed somewhere around the extremity of the image on your main LCD. If you can’t see it, press the ‘info’ button to cycle though various on-screen displays until you see all the exposure information.

It is always possible to manually select your ISO in photography. However many people also prefer to have the camera choose a suitable setting. ISO is just as important to your image as aperture and shutter speed but it doesn’t always effect an image as much. This is particularly true if you are shooting in bright conditions.

If you are still in the early stages of understanding shutter speed and aperture you are probably using shutter priority and aperture priority exposure modes. You can certainly simplify things by switching ISO to auto. Usually this is just a case cycling through the ISO settings until you get to the end. Then one more click will probably put it into ‘A’ mode. Refer to your camera’s manual it that doesn’t do the trick!

Even if you do put ISO into auto mode, you should still be very aware of the purpose and effect that it has on your photos.  Cameras don’t always choose the perfect settings when placed in automatic modes. So even then, you should keep an eye on it.

When to use high ISO in photography

A common scenario for using high ISO in photography is when you are shooting poorly lit, indoor areas and don’t want to use a flash. At low ISOs, you’ll struggle to get a fast enough shutter speed to allow sharp photos. If you increase your ISO though, you’ll be able to increase your shutter speed and still maintain the same overall exposure. Increasing your ISO by three stops would allow you to increase your shutter speed by three stops. Pretty simple stuff really.

Another common reason to increase your ISO in photography is to allow you to shoot with a greater depth of field. Perhaps when taking a hand-held landscape photo.  In this case we might increase our ISO by a few stops in order to be able to use a smaller aperture which will give a greater DOF. If you increase your ISO by three stops, you can increase your f-stop by three stops. This will still maintain the same overall exposure.

ISO in photography chart

Note that unlike f-stop and shutter speed, ISO values are never provided in half-stop increments.  Your camera will either allow you to choose ISO in one-stop, or third-stop increments.

Remember: Each step along the full stop scale equates to a doubling (or halving) of the light that reaches your camera’s sensor. In the case of ISO, this means that your camera’s sensitivity to light is doubling with each stop.

The bottom of the chart is where the future of cameras is going. We are not there yet but each year more capabilities are released.

photography iso chart

ISO quality in different cameras

We now know what ISO in photography is and how it affects the noise in our image for a particular camera. There’s a couple of other things that also affect noise.

Generally speaking, the more room a pixel on your sensor has around it, the less noise is generated in your image. This means that a camera with a higher megapixel count will have a noisier image at a given ISO. As long as all the other technology is equal. See, it isn’t all about megapixels!

Your camera’s megapixel count is simply the number of pixels that are on the sensor. The more there are, the closer together they have to be. This is the reason that full-frame cameras tend to be much better at higher ISOs.  They have a much larger sensor (50% larger in fact) in which to spread out their pixels!

On the other hand point-and-shoot cameras have very small sensors so they are really tightly packed together and therefore noisier. If you cram a huge number of megapixels onto a full frame sensor though (Nikon D810 for example), it’s entirely possible that you could end up with them being more tightly packed together than a lesser megapixel count on a camera with a crop APS-C sensor.

NB. The distance between pixels on a camera’s sensor is called pixel pitch and it’s usually expressed in microns, measured from the centre of one pixel, to the centre of an adjacent pixel.

This explains why images at ISO 800 on your point-and-shoot camera look much noisier than ISO 800 images from your DSLR with its much larger sensor.

photography tricks

Cleaning up noise

There’s a number of excellent ways to clean up your images that were shot with higher ISOs. The first is to experiment with in-camera noise reduction.  Settings are specific to your camera and manufacturer. All of them offer options to clean up high ISO noise if you are shooting JPEG.

An even better way to deal with it is to shoot RAW. If your camera allows that. Then process that file using software on your computer. Adobe Lightroom does an incredible job at cleaning up noise.

If you don’t want to buy Lightroom, or pay for Adobe’s Creative Cloud subscription, you can use noise reduction in your camera manufacturer’s editing software. Capture NX for Nikon or Digital Photo Professional from Canon.

ISO in photography is a really important part of the exposure triangle and once you master it you will be able to do a lot more with your images!

A great thing to try is to shoot in a low light setting and try to get some nice Bokeh in to. This article will help you learn all about that!


Leave your thoughts!