Photography Basics: Understanding ISO

In Tutorials by Stefano CaioniLeave a Comment

In photography, ISO is one of the three most important settings. Together with aperture and shutter speed it dramatically affects the final look of your pictures. But what is ISO and how to use it?

ISO determines how sensitive your camera is to light. The darker the environment you’re shooting in, the higher the ISO will need to be to make sure you have the right exposure.

But ISO has also the side effect of introducing an insane amount of grain (noise) in your image. Scroll to the end of this article to know in my opinion what modern digital camera with great noise reduction you can buy if you’re an entry level.

How Does ISO Work?

ISO is part of the exposure triangle affecting the brightness and darkness of your photos. If you are in a very dark room, raising the ISO value will allow the camera to capture more light whereas with a low ISO value you will get a really dark image. Very high ISO values will produce noise in your photos so be careful and make sure you don’t rely only on this setting to balance your exposure. As I said before, ISO is only one of three main aspects of photography that will determine your exposure. The other two are Aperture and Shutter Speed. If you’re interested in learning these two settings you can read my articles Understanding Aperture for Beginners and The Ultimate Beginner Guide to Landscape Photography.

History of ISO

The International Organization for Standardization introduced ISO (also called ASA before) in old film cameras as a measurement of the film speed. The higher the “film speed” the higher was the sensitivity of the film to light.

In modern digital cameras, both DSLRs and mirrorless, ISO is an electronic emulation of the same effect. Instead of having to change film in your camera you rotate a dial and select the different ISO numbers available to you. ISO is still today commonly referred by many as changing the sensitivity of your sensor, but technically this is not quite correct.

Yes, ISO does affect the exposure triangle (read next section) allowing your camera to capture more or less light depending on its value, but it doesn’t mechanically change anything inside your camera. For the most curious of you out there, because of how a digital camera is structured internally, a technical definition is that “It electronically amplifies the voltage observed at each pixel position before converting that voltage to a number. The effect of amplifying the gain of the photodetectors in the chip results in more grain in your image.”
It’s as if the light that hits the sensor is not pure light, but amplified light.

ISO and the Exposure Triangle

ISO is part of the exposure triangle in photography. The triangle represents the three elements of exposure and how increasing or decreasing one of them will require changing the other two to obtain a balanced exposure.

ISO and Image Quality (Noise)

You should rely on ISO when with the other two elements of the exposure triangle you can’t obtain the image you want.

In general you should try to stick to your “base ISO” value, in particular if you’re shooting the night sky, where your image has to be has sharp as possible. The base ISO of a camera is the minimum value available and it represents the value with which you can obtain an image with the highest quality and the least amount of noise. The lower the ISO value you use the better your image quality will be. If your camera has extended ISO values such as “LO” and “HI” I recommend avoiding them since they are simulated in-software and can ruin the quality of your picture.

What ISO Should You Use

Different situations will require choosing a different ISO value. At your camera’s base ISO value you’re not adding any gain hence no noise. For this reason for landscape photography you’ll need to shoot at your base value whenever possible. 100 or 200 is the base value of most cameras and some models also go down to 64 or 50. Remember, you don’t want to use the “LO” setting (read above). Sometimes you can’t choose a low ISO since you’re shooting in a darker environment. That’s when depending on the subject of your shooting, you could use a tripod. Using a tripod you can lower the shutter speed, maintaining a low ISO, avoid motion blur and keeping balance in your exposure triangle.

There will be situations though where a higher ISO is unavoidable. For example, if you’re photographing birds, sports or moving subjects in general and you want to avoid motion blur in your image, you can’t set a slow shutter speed. That’s when a higher ISO comes to the rescue. To combat image noise at high ISO values some digital cameras like the Sony a6000 have fantastic noise reduction, that can also be adjusted to keep as much detail as possible in your image. I can’t believe how reasonably priced this camera is on Amazon. For less than $500 you’ll also bring home a 16-50mm lens. You can find it at this link Sony a6000.


Have fun experimenting with different ISO values on the field and see how the brightness of your image will change. Make sure you keep the correct balance in your exposure triangle and feel free to post your questions in the comments below if you need help understanding these concepts.

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