When you are juggling Aperture, Shutter and ISO it’s called equivalent exposure. Understand it so you can keep those three balls in the air and get the exposure and creative outcome you want.
Let’s talk about the balancing act called equivalent exposure. Every scene has a certain amount of light in it. 
We have to make the decision. Do we assign that light to the shutter? Or do we assign that light to the aperture? So that is about exposure. How do we get the correct exposure. That’s using the exposure triangle.
In the exposure triangle we have 3 things we are working with.
1. APERTURE
The aperture controls what is in focus, how much depth of field there is. Look at a picture of this cactus. 
I have a really shallow depth of field at f/2.8 and a deep depth of field at f/22. Aperture changes the amount of depth of field in a scene.
2. SHUTTER
What does the shutter do? The shutter captures motion or stops motion. 
The shutter is moving and is about the amount of time the shutter is open. It can be open for a short time or a long time. Because of that movement it creates or stops motion. 
So, something at a half a second like water is going to blur. 
Whereas with 3 seconds it will really blur. 
Versus if you go to 1/4000 of a second that is going to stop sports action. 
Here soccer players are up in the air hitting the ball at 1/4000 of a second is going to stop that motion.
3. ISO
So what does ISO do? ISO is how sensitive your camera sensor is to light. 
100 ISO means that it is not very sensitive so it needs a lot more light. 6400 ISO means it is much more sensitive and it doesn’t need as much light. But the problem is you get noise with sensors. 
When you get up to 6400 it is going to be grainy and noisy and cause a problem.
So there is the aperture, the shutter and ISO. That is our exposure triangle. So now, what is a normal exposure? A normal exposure is when the image has correct highlight and correct shadows. The highlights aren’t too bright. The shadows aren’t too dark.
Look at this example of what a normal exposure is. (f/22, 1.6 sec, 100 ISO) Normal exposure is what we are going for. To find a normal exposure, here we have it at 1/15 sec and f/16. That is a normal exposure.
Equivalent Exposure
Now let’s talk about equivalent exposure. I am going to use my exposure wheel. On the outside ring I have my shutter speeds and on the inside ring I have my apertures. So the first one I have a shutter speed of 1/15th of a second and I have f/16. What this does is every other set on the exposure wheel are correct exposures. 1/30th with f/11, 1/60th at f/8, 1/125th at f/5.6, etc. So how I have my camera set up at f/16 I have deep depth of field and 1/15th of a second. The shutter is dragging. 
So that means the motion in my scene is going to blur. And I am going to have deep depth of field. This gives us the ability to make a decision about motion on the outside of the exposure wheel and depth of field on the inside of the exposure wheel. 
I can have a lot of depth of field or very shallow depth of field. That is called equivalent exposure. There is a look at equivalent exposure using the exposure wheel.
We have a copy of this in our member area you can download. Check it out. It is a great thing to have in your bag to carry with you.
Now let’s go back to some examples using our demonstration right here. My first image is a portrait of a woman. In this portrait I want a shallow depth of field. My concern is not about stopping motion because she is not moving. 
My concern is to get rid of the depth of field. I want a shallow depth of field. So I am going to go from f/16 to f/2.8 at 1/500th of a second. Now I have a shallow depth of field and ability to have beautiful bokeh behind her. I am using a longer lens and that makes it look really nice.
The next is a shot I did of Jodie Sweetin of Fuller House. In this scene we have a kitchen out of control with crazy things happening in the background. I want a deep depth of field so we can see what is going on back there. We want to see the sink and the fire and everything. I don’t want a shallow depth of field. I need more depth of field. So I am going to change the aperture to f/8. That will give me a nice look at the background and yet not give me too much depth of field but enough to be able to see what is going on in the background to give me a nice image. Now my shutter goes to 1/60th of a second. Which is absolutely fine because there is not a lot of motion there. There is a little motion out of the water in the sink. But not so much to create a huge issue and that 1/60th of a second will let that blur a little bit.
The next shot we have here is a sports shot. I need to have a fast, fast shutter. I don’t have enough exposure here. I need to change the ISO. Changing my ISO allows me to go up 1/4000th of a second. And I have to add at least one stop to get f/2.8. So I am going to push my ISO up to 3200 in order to make those settings work. To be able to give myself a fast shutter to freeze the action and f/2.8 to give me a shallow depth of field. I want the people behind the soccer players to go out of focus. Those are the setting I need to I had to go to the ISO bucket to be able to make that happen.
Now as we move from that sports shot to where we want a fast shutter and shallow depth of field, we go to a nice water fall shot by Cheyne Walls. 
We actually have a download shot by Cheyne Walls that you can get over at our store at online courses. Go to TheSlantedLens.com/landscape. Check out that download in the online courses. Anyway, Cheyne likes to shoot with long shutters to blur the water. Because of the stuff in the foreground we need a smaller aperture. We will go up to maybe f/5.6. We have to get rid of all of this exposure. 
Remember we were at ISO 3200. We will dial our ISO back down to 100 ISO. This will get us down to 1/8th of a second with our Shutter. That will give us the beautiful water fall with the blurring water.
Now it is time to apply this information that we have learned to this image we have here in the background with Jerimiyah. 
Let’s get him in here and shoot some shallow depth of field and deep depth of field, motion blur and stopping motion.
Let’s take a look at some other examples of images that were shot and see what the camera settings were.
That concludes our 3 part series on Shutter, Aperture and Equivalent Exposure. I hope you have gained a deeper understanding of the exposure triangle. Now when you get asked questions about what camera setting to use you can think about what you want to accomplish and that will help you decide what your camera settings need to be. 
It gives you the power to know. That is the question I get asked more than anything else, “What should my camera settings be?” Understanding the exposure triangle and understanding the shutter and what it does, aperture and what it does, and equivalent exposure and what it does allows you to decide what camera settings you need for a particular image.
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