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Finally Understand What ISO is, and How it Affects Photos

October 28, 2020

I'm Chelsy, a single mom in a small town, who loves photographing weddings, and helping photographers build their own businesses

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When you first get your camera and want to learn how to use it you probably took to the internet.  Because who has time or patients to read a user’s manual?!  Trying to figure out how to use your new camera can be frustrating. There are all these terms like ISO aperture, shutter speed, white balance, exposure compensation, the list goes on By now you may have stumbled over something called the exposure triangle.  

What is the exposure triangle? 

The exposure triangle is made up of three things ISO, Aperture, and Shutter Speed. Today we are going to be focusing on ISO.  For me, this was the tricker one for me to wrap my head around especially when you see most people explaining it simply as how sensitive your camera is to light.  

While technically that is correct, that explanation didn’t really make sense to my very visual brain. I had to reach back into  the filing cabinets of my brain to a photography class I took in 4-H when I was 8.  Now this was back in 1999 so while digital cameras were available they were still very expensive so this was actually a film photography class at a local camera shop in Salina, KS. 

Our instructor was explaining how film worked and what the numbers meant.  Choosing your film is very much like choosing your ISO.  The higher the number the more sensitive your film or your camera is to light.  – Now this doesn’t really help because that’s the same exact explanation you see everywhere else.  

A visual for how ISO works 

The way I learned is you can think of a sheet of paper as your photo if you choose an ISO or a film of 100 you can imagine 100 circles on a page.  Each of these little circles soaks up light.  The more circles there are, the more light the photo soaks up. 

this represents an ISO of 100
This represents an ISO of about 400
This represents an ISO of about 1500
side by side of ISO 100 left and ISO 1500 right

This also helps to visually see how grain in photos happens. 

Camera settings: 1/200 sec f2.8 ISO 1250
Lens: 105mm 2.8

As you get more and more little circles they start to crowd each other, and that crowding causes little distortions in your photo called grain. All the little circles get a little smooshed, and they start to almost overlap. Here is a photo example of what grain looks like if we were to zoom in close.

Camera settings: 1/200 sec f2.8 ISO 1250
Lens: 105mm 2.8

See how on the photo above on the wall there are little specs? That is grain. That is where these circles are squashing up against each other to capture enough light to expose the photo. This photo was taken at a courthouse wedding with very little light.

Why higher ISO?

So why would you ever crank up your ISO to something like 2000?  Well sometimes you are in situations where you need to balance out your exposure triangle with a higher ISO. This can happen when photographing a quick moving subject in a dark setting. You need your shutter speed quick enough to freeze the motion, and your lens is already maxed out on how wide it opens with your aperture, so you bump up your ISO in hopes of not getting too much grain, and having a photo turn out. 

Photography is an art form!

Some photographers love the grainy look, and this is where your own shooting style comes in.  The one thing about photography is you have to know the rules to break the rules, this is true in any art form really! — I think new photographers start to dig into what technically makes a photo correct that they often forget that photography is an art form and it’s okay to break the rules.  But you have to know how the rules work in order to get the photo you are trying to achieve, so you know what to change or adjust. 

DSLR vs Film

One of the beautiful things about DSLR or digital cameras is you can change your ISO whenever you want. On film cameras you set your ISO when you choose what film to use, and you are stuck there for the entire roll of film. 

Whenever I am getting my settings set for a shoot, or to take photos of my kids, I always set my ISO first.  Often I won’t need to change it once I get started, especially if my lighting situation stays consistent.  If however the sun starts to set, or some dark clouds roll in I may have to bump up my ISO.  

Stay tuned for upcoming blog posts all about aperture and shutter speed! 

So did this visualization help you to understand ISO a bit better? Let me know in the comments!

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  1. Very helpful ISO tips, Chelsy. This is applicable to videography as well.

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