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To switch the camera into Aperture Priority Mode, is usually a dial on top of the DSLR. So for example, on the Canon camera, we can simply switch it here, from the green square, or wherever it might be, into the AV mode. And AV stands for Aperture Valuation. On the Nikon, it's simply the letter A, A for Aperture Priority. And on the Sony, it's also an A, again an A for Aperture Priority. But what this means, is that you as the photographer are going to choose the aperture for your picture, and the camera is going to automatically choose the shutter speed to go along with it. So let's talk about what an aperture actually is, and what happens to the shutter speed when you change the aperture.
If you look at this lens here, as you're looking through it, as I start to rotate the aperture dial, you'll see that there is a series of leaves inside of the lens that are closing down, those are called the aperture leaves. As I open it back up, they get bigger and bigger. Now, as you can imagine, when it's wide open, a whole lot of light is coming through, the maximum amount of light possible is coming through that lens. As I close it down, we restrict the amount of light coming in, so less light is coming into the lens at once. So first, let's talk about what happens to the shutter speed. When the lens is wide open, when the aperture is at its biggest setting, as much light as possible is coming in.
So that means the shutter has to be open for a less or a shorter amount of time. As we close the lens down, close down the aperture to a smaller hole, less light's coming in at once, so to make it a proper exposure, the shutter's going to have to be open for longer. So if you want to have fast pictures, you generally want to have the lens wide open at it's biggest apperture setting. That's going to give you the fastest shutter speed. If you want to have a slower shutter speed because, for example, lets say you want to have a motion blur in your photo, then you're going to need to close the lens down a little bit to restrict the amount of light coming in.
So one of the other things that changes when you change your aperture, is something called depth of field. That is, how much is in focus. So with a very large aperture, you have a very shallow depth of field. Now, shallow depth of fields means that, if I'm photographing from here pointing this way. Only a very narrow band of information is going to be in focus. So, this is great if you're shooting a portrait, for example, and you want the stuff behind the person you're shooting to be blurry. If you have that large aperture, you going to have a shallow depth of field, and that's going to give you that really nice pleasing view for a portrait. However, if you're shooting something like a landscape and you want to have a whole bunch of stuff to be in focus at once, you want to go the other way. You want to stop the lens down, you have a smaller hole which is going to give you a bigger depth of field.
Now, how do you remember all this? Because we're talking about aperture being bigger and smaller, and these numbers, and what do these all mean. Well, first of all, let's talk about the actual numbers. If you look at this lens again. If I take it down to the smallest setting, at 1.8, that's the number 1.8 on the lens. If we take a look at that, you'll see that that is actually wide open. So the smallest number is giving me the biggest hole. hold on a second. How's that? Well, let's just verify this. I'm going to take this lens now, and go the other direction, all the way down to f 22. And now, let's take a look at it again. And as you can now see, we're looking at the smallest hole, or the smallest aperture that this can make.
So how come a bigger number makes for a smaller hole, and a smaller number makes for bigger hole? Well, it's actually a fraction. It's F over that number. So here's the easiest way to remember this. If you want a small depth of field, choose a small number. If you want a big depth of field, choose a big number. So shallow or small depth of field is a small number. Big broad depth of field is a big number. That's the easiest way to remember that. And if you can keep that in your head, that's all you have to know when it comes to shooting an Aperture Priority. So now, let's talk about a couple of different scenarios where you might use a particular aperture.
What type of an environment you'd be in, or what type of thing you might be shooting. So let's start with the settings. A low number meaning wide open, is something like f 2 or f 2.8 of f 4 maybe. Just depending on the lens that you have. As far as the when and why, generally you're doing that if you have low light. Or if you just want to have really good shallow depth of field. And so that's the result of that. You get that nice shallow depth of field which is great for portraits or anywhere you need a high shutter speed. If we go the other direction the high number, or the stop down, giving us something like f 16 or 22 or 32. Generally we have so much light that we need to restrict it, or we want that really, really big depth of field for things like the scenic shots. So once again depending on what aperture you chose will really depend on the scene that you're shooting.
Portraits generally you want to have that shallow of the field, scenic you want to have a bigger depth of field. Now of course there's no right answer and there's always somewhere in between. So this is something you just have to play with and you get to know your lense and your camera for the type of environment that you're shooting.
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