What is ISO? AKA The Blog Post That Will Put You To Sleep

Let’s break down ISO!  What it is, what it does, and how it affects the outcome of the photos that you take.

Short Explanation:

ISO is one of three points of the Exposure Triangle.  If any of you took a film photography class in high school or college, you’ll remember film speeds – same concept.

ISO is a measure of the sensor’s sensitivity to light.  The higher the number, the more sensitive the sensor is and therefore the less light you need to capture your image.  If you increase your ISO, you can more easily capture an image in a low light situation, however, that comes at a price – the higher the ISO, the more “noise” (visual distortion) you’ll see in your final image.

The lower the number, the less sensitive the sensor is, so you’ll need more light.  The image, however, will be very clear.

ISO explanation and example

Long Explanation:

Boring background:  ISO stands for International Standards Organization, which is one of the three measures of measuring camera sensitivity. It harkens back to the film days when you used to be able to buy film in varying ISO’s depending on the lighting conditions you were working in. The darker the place you were photographing in, the higher the ISO you needed to make photos. The higher the ISO, the more “sensitive” the film was to light.

With the advent of digital photography, the ISO is changeable in your camera in a snap, allowing you to choose exactly how much light reaches your camera’s sensor. No more switching out film when you change lighting conditions! Because this was such a common term with photographers, the name ISO remains today.

(Is your brain numb yet?)

Most DSLR cameras will automatically choose the ISO for you. However, when we are learning how to use our cameras, we really want to take back control over this function.  We didn’t buy our DSLR cameras to just keep shooting on auto, right?

What is an ISO Value?

Digital cameras have ISO values of 100, 200, 400, 800 and 1600 as a standard. Higher end digital cameras can go as high as 409,600 (but you really don’t want to do this)!  Note that these values essentially double every time you go up in ISO, so that means that 800 ISO is twice as sensitive as 400.

How ISO Affects Exposure

We’ve talked before about the Exposure Triangle (ISO, shutter speed and aperture) and how each element impacts each other when we take a photo. When we increase our ISO, we can speed up our shutter (to capture motion) or increase our f/stop (to obtain a larger slice of focus). Let’s talk about a scenario where this would be helpful.

You’re on vacation and in a beautiful cathedral, and it’s dimly lit. You want to take photos, but you don’t want to use flash because you know it will overpower the soft, glowing light in the cathedral. When you expose for the scene, your camera tells you that at ISO 100 you’ll need an exposure time of 1/15th of a second. From our lesson on exposure, we know that the shutter speed of 1/15 is way too slow, and you would need a tripod so that the photo would not come out blurry. You don’t have a tripod, so what can you do? Increase the ISO.  When you increase the ISO to 400, you’ve increased the sensitivity of the light hitting your camera’s sensor by four times. The next camera reading at 400 ISO tells you that the shutter speed will be 1/60th of a second, which is a perfectly acceptable speed to hand-hold your camera without a tripod.

The Downside of Higher ISO

Alas, that increased sensitivity comes at a price.  Whenever you increase the ISO on your camera, it increases the digital noise in your photograph. Noise is roughly equivalent to what film grain was, meaning there will be tiny colored microscopic dots interspersed in the image. While these may not be problematic in smaller photos, it can be noticeable in larger prints, especially in the darker areas of the photo. For that reason, you want to use the lowest ISO you can to reduce the possibility of digital noise.

Now that you understand the basics of ISO, take your camera out in some dimly lit situations and see how raising and lowering the ISO changes the look and feel of the images you create.  Be sure to pull the images onto your computer so you can get a closer look at the noise.

Asleep yet? 🙂

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