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In Photography, What is ISO?

And why should you care?

By Darryl BrooksPublished 3 years ago 5 min read
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Photo by Lina Simonian on Unsplash

The history

Remember film? If you took photographs way back in the dark ages, you remember buying film. It came in a box, probably yellow, but possibly green and it had a big number on it; 100, 200, 400, etc.

These numbers were the ASA speed of the film. ASA stood for the American Standards Association, which set standards for a wide variety of things. The higher the number, the ‘faster’ the film, or the more sensitivity to light. If you accidentally bought some ASA 1600 film (not likely as it was expensive), your images turned out grainy. This was the analog equivalence of digital noise. If you needed to shoot with a faster film, you took one roll out of your camera, possibly losing the rest of it, and put in a fresh roll at the correct speed.

Today, in digital cameras, the sensitivity to light is adjustable in-camera. You do this with a setting called ISO. ISO stands for International Standards Organization. Just like with film, ISO is classified and numbered the same way. On the low end, most cameras operate at ISO 100, the same as the old ASA 100 film. Many newer cameras go lower. On the top end, well, that changes every year. Suffice it to say it is higher than you are likely to need unless you are photographing ghosts in an unlit room.

Modern Use

The speed of the sensor, just like the speed of the film, has always been part of the exposure triangle. The exposure triangle consists of aperture (the size of the hole that allows light in), shutter speed (how long that hole stays open), and ISO, (the sensitivity of the sensor to the light).

As with the other two factors, we measure ISO in stops, and just like the other two, each stop doubles or halves the amount of light. But each factor also affects other components of the image. I will cover in another article the relationship between aperture and shutter speed. In this one, we will focus on ISO.

Again, each ISO setting doubles or halves the amount of light, or in this case, sensitivity to light that hits the sensor. So, ISO 200 is twice as sensitive to light as ISO 100, so you could shoot at a faster shutter speed or a smaller aperture. So why not just crank it up to 64,000 or higher and leave it?

Remember the grain we talked about in film? It’s still here, and now it’s called noise. With each new iteration in camera technology, the noise is getting less, and post-processing software is getting better. But it’s still the fact that the higher the ISO, the noisier the image. It is entirely up to you what is an acceptable level of noise. Some people like the retro look of a noisy black-and-white image.

However you feel about noise, I think it is better to get the image, noisy or not, than miss it, or have it too blurry, because there isn’t enough light.

Sasquatch may disagree.

How do you use it

Most beginners and many hobbyists leave their cameras in some variation of automatic mode. This means the camera will always decide all three factors and change them on each shot as needed. In my opinion, ISO is probably the best reason not to do that. Many cameras and most cellphones, will crank up the ISO before adjusting other factors when the light isn’t good. That’s why most cellphone images look plasticy; too high an ISO coupled with too much noise reduction.

Some professional photographers always shoot in manual mode. They will manually set all three factors and then adjust one or more when the light or situation changes. Personally, I only do this when shooting with strobes or flashes, or in very unusual lighting conditions.

Many photographers, including myself, shoot in either aperture priority or shutter priority. This means you select one of these factors and the camera selects the other. Easy, right? But what about ISO?

Well, unless you select Auto ISO (which I will cover in another article), you select that as well. So in one of these modes, you are actually manually selecting two sides of the exposure triangle and the camera is selecting the third.

So what setting is best? As with almost every question in photography, the answer is, it depends. But usually, you should digital noise, so a lower ISO is best. Rather than fiddling with this setting all day, I tend to set it at once and leave it unless there is a major shift in the light.

No matter which mode you shoot in, you always need to double-check your settings as the light changes. I usually shoot in aperture priority with my ISO set as described below. This means the camera will select the shutter speed. But I check that shutter speed with every shot to make sure it isn’t too slow. If I move into the shadows and the camera drops the shutter speed to less than 1/30th second or so, that’s a problem. In that case, I have to adjust aperture or ISO. Which one? You guessed it; it depends.

On a sunny day outdoors, I usually leave it at ISO 100. Having said that, if the clouds are variable, or I will be in and out of the sun and shade, I may put it at 200, to make sure my shutter speed doesn’t drop too low. With newer cameras, I have no problem leaving it at 400. At 800, you will be introducing a little noise, but not enough to worry about.

If it’s overcast, or I am in the city in the shadow of buildings, I always go with 200 or 400. Inside, it just depends. That’s typically a guessing game and a balance between aperture, shutter speed, and ISO.

Most photographers with any experience are familiar with and know how to use aperture and shutter speed. But ISO is the third part of that triangle and we must take it into account. Learn how to select the best ISO for each situation and raise your photography to a new level.

If you enjoyed this article, please give me a like by clicking the Heart, and if you really liked it, consider dropping me a tip below. Thanks for reading.

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About the Creator

Darryl Brooks

I am a writer with over 16 years of experience and hundreds of articles. I write about photography, productivity, life skills, money management and much more.

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