Photography Camera ISO Explained

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ISO is part of the Exposure Triangle along with Aperture and Shutter Speed. ISO affects your camera’s sensitivity to light, but also the amount of Noise/Grain in an image.  In a previous article I explained Aperture and the role it plays in DSLR photography and the Exposure Triangle. Here we will take a close look at understand ISO.

What is ISO?

ISO is basically the level of sensitivity your camera sensor has to the light that is available when you’re shooting. When there is a lot of light available such as direct sun, your camera doesn’t need to be very sensitive to the amount of light available. If you are shooting at night or indoors, your camera will need to be more sensitive to the amount of light available.

The more sensitive your camera is to the light available, the more flexibility you will have in exposing your images correctly in low light situations. However this does introduce another issue, grain/noise.

How ISO Effects Grain and Noise

The lower the ISO Number, the less sensitivity it has to light and the less grain it will have. This is why you will shoot with a lower ISO when using Flash, or shooting in Daylight or wit Studio Lighting conditions.

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When shooting in low light situations, such as indoors or at night, you will need a higher ISO range to get the shot, and to be able to auto focus properly.

Lincoln Memorial Photography by Roberto Blake

Lincoln Memorial Photography by Roberto Blake

What Do ISO Numbers Mean?

Every camera has a base ISO number. This number is the number the camera can shoot at in terms of ISO and produce the sharpest image without introducing noise. For most cameras in the Canon and Sony Alpha series this will be ISO 100, for many entry level Nikon Cameras this will be ISO 200.

In the era of traditional SLR film cameras, ISO had an impact on the speed at which you could shoot. ISO 800 film and up were referred to as “high speed film,” because you could shoot at higher shutter speeds in most situations. Each number in the ISO range doubles the sensitivity to light starting from the base: 100, 200,400, 800, 1600, 3200, and so on.

Potomac River Photography by Roberto Blake

Potomac River Photography by Roberto Blake

If a properly exposed image had the following settings, Shutter Speed 1/500, ISO 400, and Aperture F/4; then changing the ISO to 800, would mean to properly expose the image you’d need to also double the shutter speed to compensate for making the camera twice sensitive to light, or the image would be blown out.

When to Maintain a Lower ISO

You can compensate and not go to higher ISO in low light situations by shooting with a wider Aperture, or if you’re using a tripod or monopod for stabilization you can use a slower shutter speed. You can also use the dragging-the-shutter technique and use a slower shutter speed while using a Flash.

If you are shooting at a low ISO in daylight and the image is still over-exposed and you cannot compensate by adjusting your shutter speed or aperture (due to the look of the shot you want), you can use an ND Filter in order to remove several stops of light and get the shot you need.

High End Cameras and High ISO Ranges

If you are shooting a lot of action and fast moments such as sports or dance, then taking advantage of a higher ISO is a must. But what about grain and the quality of your images? This is where the pro’s advice about making an investment in your camera gear comes into play. High-end cameras like the Canon 5D Mark III or the Nikon D810 (or even the D4s) are made to shoot at the higher ISO ranges without destroying the quality of your images in these situations.

Notice the amount of grain in the image below. While the overall image is still very clear, the shelves have noticeable levels of noise and grain to them.

Photography by Roberto Blake

Photography by Roberto Blake

Portrait photographers can get away with shooting on entry-level camera bodies in controlled lighting or natural lighting situations with still models. But if you want to shoot action and sports, high-end camera equipment and fast lenses are going to be essential to you.

So now you should understand ISO a bit better and how it relates to aperture and shutter speed in the Exposure Triangle. ISO not only effects the overall level of light/exposure regarding your image, but the Noise/Grain as well. It also can directly impact the shutter speed you are able to shoot at to capture a moment.

Mastering the Exposure Triangle is the key to getting out of shooting in Auto modes with your camera, and taking control of your images so they look great right out of the camera, before you take them into Photoshop or Lightroom.

Roberto Blake is a graphic designer helping entrepreneurs and small businesses improve their branding and presentations. He also teaches graphic design and Adobe tutorials through his YouTube channel and community. See for more details.
  • Ian Pack says:

    Interesting piece Roberto, thank you for sharing. As far as I’m aware ISO has no effect on the ability to auto focus in low light. Auto focus fails to work in low light as a result of less than ideal light levels and lack of contrast for which the focus sensors use to determine focus.

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