ISO

Before we start I want to share this link to ‘Canon Explains Exposure’ this is great to play with and get familiar with how all three settings work together.

So far we have looked at Aperture and Depth of field and also Shutter Speed and Motion. Now let’s take a look at ISO and what part it plays in exposure.

Back when cameras used film, ISO or also referred to as ASA, was used to refer to the sensitivity of the film to light. Lower numbers indicating less sensitivity, for example, ISO 100 would be less sensitive and therefore ideal for sunny or really bright situations, ISO 400 would be more sensitive to light and used mostly for lower light conditions such as indoors. You could also get film with lower than 100 ISO and higher than ISO 400, such as ISO 800, ISO 1600, however, the higher the sensitivity the more “Grain” or nowadays we call it “Noise”. When digital photography came about, the way ISO was measured stayed the same. Meaning that if you dial in ISO 100 it will be less sensitive to light than if you dialed in 200 ISO, each step gets more sensitive 400,800,1600 and so on. Again, just like film, the higher we go with ISO the more noise we see in our image.

For detail, it is best to shoot at the lowest ISO possible, reducing the noise and keeping the image sharp and clear. In some situations, you will need a higher ISO to use certain settings in certain situations, for example, low light environment and you want to freeze motion, this means a fast shutter speed and also means less light getting to the sensor in an already low light situation, so by increasing the ISO we increase the sensitivity of the sensor and can pick up more light more quickly to get a good exposure.

So let’s have a look at a series of images taken with each ISO from 100 to 25600 to see how and when the noise starts to become a problem. For this activity, I am using a Canon EOS 200D and have taken an inside shallow depth of field image and an outside deep depth of field image to compare differences.

In the above images, I believe up to ISO-1600 is not bad, a lower ISO is obviously better but sometimes we just don’t have the light. The camera and subject are still so shutter speed wasn’t an issue in this image, you could just choose a longer exposure rather than sacrificing quality.

In these above images, I chose a deeper depth of field. I believe up to ISO-3200 is ok, there was a slight breeze and plants were moving slightly, if you were happy with a little blurring, a lower ISO and longer shutter speed would still be ok but to freeze motion a higher ISO may be needed to bring shutter speed down. Next, I’ll go back inside to lowlight conditions, I,m going to keep the aperture the same(f/7.1) and shutter speed at a high enough speed to freeze motion(1/80sec) and just adjust the ISO to show the difference.