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Arriving at the best exposure for a photo is part science and part art. In Foundations of Photography: Exposure, Ben Long helps photographers expand their artistic options by giving them a deep understanding of shutter speed, aperture, ISO, and all other critical exposure practices. This course covers the basic exposure controls provided by all digital SLR cameras, as well as most advanced point-and-shoot models. Learn how to master a camera's metering modes, how to use exposure compensation and bracketing, and much more. By the end of the course, you'll know how to develop an "exposure strategy" that will allow you to effectively employ your exposure knowledge in any shooting situation.
If you have been through the Shutter Priority lesson, this lesson ought to make a lot of sense to you. We are going to talk about aperture priority. In aperture priority, I can select an aperture that I want, and when I meter, the camera will always select a corresponding shutter speed that will give me a good exposure, meaning an exposure that is neither too bright nor too dark. Changing my camera to Aperture Priority mode. If you are not sure how to do that, you ought to check out the Modes lesson. The reason I might take control of aperture is that aperture is how I control depth of field.
And as you have seen, depth of field is simply the measure of how much of my image is in focus. So let's take a look at our scene here. We've got three antique cameras, all at three different depths. So I can choose to shoot these in a lot of different ways. I can have them all in focus, or I can have just some of them in focus. So, the key to shooting shallow depth of field--that is, so that only some of these things will be in focus-- is to use a wide aperture. So I am going to dial my aperture down as far as it will go, to f2.8. Now the max of my aperture is going to vary from lens to lens.
On this lens, I can get it all the way open to F2.8. Now, that means that I am going to have a very shallow depth of field, meaning that after a point, things are going to be out of focus. That does not mean that my depth of field starts here at the end of my lens and maybe it goes to about here, and all of this stuff is in focus and everything after it is out of focus. Depth of field is always measured around the point of focus in your scene. So if I focus right here, and I have got this much depth of field, then only these things will be in focus. If I focus right here, and I have got this much depth of field, then all of these things are in focus.
But if I focus right here with this much depth of field, I can move that depth of field by changing my point of focus. So I could focus here and get this, or I could focus here and get this. So let's take a look at that in action. I am going to start by focusing on the center camera. So it focused. I have got my aperture dialed in to F2.8, and I am going to take the picture. And sure enough, what I have got here is my center camera is in focus, the rear camera is out of focus, the front camera is out of focus. I have got a depth of field of maybe a foot, maybe a little bit longer, and it's centered right in the middle of my scene.
Everything outside of that area to the front and back is out of focus. So now let's try shifting the focus to the front camera. Now I am going to do a little trick here that you haven't actually learned, but you can learn about in the "Foundation of Photography: Lenses" course. I am using only the center autofocus point on my camera. I configured it that way, and so I am setting focus on the front camera. Here again, I have a very shallow depth of field. My depth of field is actually as shallow as it was before, but now it's centered around the front camera, so the back two cameras are out of focus.
Let's try this again, and this time let's focus on the rear camera. Turning the wrong knob on my tripod there. There we go. So I have got that focused, line up my shot, take the picture, and t here we go. The rear camera is in focus, the front two cameras are out of focus. So that's a very simple way of shooting shallow depth of field. Now, let's look at making our depth of field little wider. I am going to change my aperture. I am going to bump it up to F8. That's several stops higher. And what that's going to do is give me a wider depth of field.
That's going to give me a depth of field about this wide. And again, if I am focused on the center, that's going to mean that maybe a little bit of this camera will be in focus, maybe the back end of this camera, and this camera will be on focus. Everything in here will be in focus. Everything out should be soft. So with my focus on the center camera, I take my shot, and sure enough, my center camera is in focus. The front and rear cameras are blurry, but they are not as blurry as they were before. My depth of field has gotten a little wider.
Now, let's say I want everything in focus. To do that, I am going to go up another stop to f11. That should give me a depth of field about this wide. And again, if I were to focus here with depth of field this wide that would mean that this camera would be on focus, and this camera would be on focus, and that one would be out focus. So I am going to be sure in focus on the center, and that should get me all of this. So my aperture is at f11. Again, larger number means smaller aperture, smaller aperture means more depth of field. That's all we are doing here.
Focus on the center, take my shot and sure enough, everything is in focus; all three cameras are in focus. You will also see that the table is sharpening up on the edges because it all fits in my depth of field. So this is the power of depth of field control. I can render some things blurry, some things sharp. This helps me control the viewer's eye. It helps me bring attention to very specific things in my image, which is at the essence of good composition. I do that by changing aperture. Now when you are ready to go out and shoot really deep depth of field or go out and shoot really shallow depth of field in trickier situations, you will need to know a few more things, and we will be covering those later.
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