Today we’re looking at the third part of the exposure triangle, ISO.

There are three ways your camera can get light for an image

  1. Open the Aperture in the lens – See Beginners Guide to Phtotography part 1 – Aperture
  2. Open the shutter speed – See Beginners Guide to Phtotography part 2 – Shutter Speed
  3. Enhance the available light – this guide.

Aperture and Shutter Speed both control how much light gets into the camera. ISO is a little bit different. ISO controls how sensitive the camera sensor is to light.

If ISO is low, the camera will be less sensitive to light, if ISO is high the camera will be more sensitive to light and the image will be lighter.

ISO is used when there is not enough light, so by increasing the camera’s sensitivity to light, we can work with lower light.

Sounds great right?

But… there’s a downside too.

When ISO is increased, it makes the image lighter, but it also makes the image noisier.

ISO infographic

ISO and Noise

Think about listening to music through a small speaker. When you turn it up full the sound quality deteriorates. Well, it’s the same with an image. When ISO is increased, the image quality deteriorates. Random coloured pixels appear in your images, especially in darker areas. These make your images look grainy and less sharp.

This image was taken on a dark afternoon indoors, away from the window. The ISO is a whopping 12800, which is the second highest option for my camera.You can see the image is very degraded due to the large amount of noise, even though I have applied noise reduction in Lightroom.

Before I reduced the noise, you can see that the image quality is not great.

What ISO setting should you use

For most camera’s, ISO starts at 100 (some start at 50). If you have enough light, use ISO 100 wherever possible, as this will result in no noise (provided your image is correctly exposed).

So if you’re shooting on a sunny day outside, you can use a fast shutter speed and still have enough light in your camera.

ISO is usually the last thing I change when I am choosing my settings. Firstly I’ll set my aperture to get my desired depth of field, then I’ll set my shutter speed high enough to prevent motion blur.

if it’s dark and I do not have enough light, I will try to open my aperture and decrease my shutter speed. I don’t want to decrease my shutter speed too much, or I will get motion blur, so at this point I will increase my ISO.

Don’t be afraid to boost your ISO. Yes, it can introduce noise into your image, but sometimes this is necessary in low light. 

If you need to boost your ISO to get the correct exposure, do it. It’s better than underexposing your image, because when you try to lighten an underexposed image, this will cause noise too. So boost your ISO, that’s what it’s there for. 

What is the Maximum ISO setting I should Use to Avoid Noise?

Different camera’s handle noise differently, some are better at it than others. I sometimes here people say that Nikon handles noise better than Canon, but having only shot Canon, I can’t tell you whether that is the case.

Older and entry level cameras have smaller ISO ranges, up to around 1600, whereas newer and professional level cameras have massive ranges, up to 51200.

Whatever the maxiium ISO for your camera. I recommend sticking to the low and mid range ISOs. At their maximum, whether that’s 1600 or 25600, image quality is very reduced.

Practice using your camera at different ISO levels and see how your camera performs. It’s also about personal taste. How tolerant are you to noise in your images. Personally, I can cope with noise up to around 1600 on my 5d mkii, but I’m usually not happy with anything higher.

It’s helpful to know your camera and your preferences, so you can adjust your settings accordingly. For example, if I am shooting in low light and I need to boost my ISO above 1600, I will usually look for better light, get my speed light or accept that it’s too dark for photos.


Native ISO and Expandable ISO

When you’re shopping for a camera, you’ll sometimes see the ISO listed like this:

ISO Sensitivity: Auto 100-32000, ISO can be expanded to L:50, H1: 51200, H2: 102400

Camera manufactures give two ISO ranges, auto or native ranges, and then an expanded range, which is a lot higher.

Why? Well it may be cynical of me to say, but high ISO sensitivity can be a great selling point for a camera. B

ig numbers look impressive and boost the specs of the camera. The trouble is, often those super high ISO’s make images look a bit rubbish. The noise levels are just too high.

So when you see auto and expandable ISO ranges, take it with a pinch of salt and know that the expandable range probably came from the marketing department. Try to use your auto ISO settings as much as possible as you’ll be far more likely to get a usable image.



How to Reduce Noise in An Image

The best way to reduce noise is an image is to look for better light so you can reduce your ISO. If that’s not possible, Lightroom has a great noise reduction slider that does a great job of reducing noise. Don’t go too nuts with it though, as you also lose sharpness. I tend to increase the luminescence slider to 20 to 30, any higher and the image becomes soft. Lightroom Noise Reduction