 So have you ever wondered what it is that makes some images have really blurry backgrounds and others not? In this image you can see, for example, I made a background that's really blurry and in the foreground I've got like a very small area of my photograph that is in focus. The reason I did this is because I wanted to focus on this little fern kind of guy sticking out of the wall of a barn that I saw and for some reason thought that was cool. And how I did this was by setting an aperture that would allow me to do that. So let's first write out aperture and make sure I spell it right. I always misspell this word. And then we're going to take a look so the aperture is the thing that I was manually setting in my camera that allowed me to have this look. But the thing that I'm actually controlling what is actually being changed here is called the depth of field. So depth of field. Now the depth of field is just basically what is in focus. It's a definition of what is acceptably in focus. I think if you look it up it says the range of things in an image that are acceptably in focus beyond a certain focus point. So my focus point is right here and I've said okay. So things in this little area right here are acceptably within focus. So that is my depth of field. Everything outside of that is out of focus. Now this is determined by again the aperture and this image I think I was shooting somewhere around F, somewhere between F 2.8 and maybe F 3.5 somewhere in there. I could maybe go look it up but I'm just looking at it and know what I was shooting anyways. Now I can go and take another look at another photograph that I was going to use as an example for this lesson. And this is my sister and her husband as an engagement photo I took. You can see here that the depth of field is much deeper. So here you can see that the clouds are in focus. They're in focus and in grass it's all the way like really close up to the camera is in focus. Now there you can see there's also pieces of grass that are not in focus like this one right here that's like basically laying on top of the lens. Not in focus so much but as you move back into the photograph things focus in a little bit. And this was the result of a higher F stop. So I shot this photo at around F 8 which means that I had a very deep field of focus which means that there was a big deep area in the photograph that was in focus. So the best way to think about your aperture is to imagine it being a window into your camera. So you've got your window just like a window on a house and you have bigger windows and smaller windows. Now bigger windows have numbers on them like F 1.4 or maybe F 2. Smaller numbers are things like F 8. So that's like a pretty small little window and you can see on this diagram how that works. Now because of the size and because of the way that light travels through lenses and things like that as you move down this ladder or as you move across the scale or whatever you want to say each one of these steps allows half as much light into the camera. So you'd need twice as much time to exhaust that which means longer shutter speeds. That's why this is going to affect our metering lessons and our exposure lessons later on in the course. But the important thing to know is that as you're moving towards F 22, so F 22 is at the very top of this. You can imagine how small that is as you move along. As you move in that direction you're having less light come into the lens but as a result you're seeing more things in focus. So at F 1.4 you know you have a little field of focus like right that, like that. And at F 8 you have a field of focus that's like that. So you have much more in focus and maybe here at F 4 you have a smaller one like this and maybe F 2.8 it's like more like that and it's moving down towards the size right here. So that's you know kind of looking like this maybe if your subject is right here. So that's how that works and just important to remember that amount of light coming in and the focus and how they're related to that number. Here is what it looks like on a real lens. This is actually an old menalta lens back in the day. You could actually just take a look through them and see what the world looks like at F 1.4 or F 22. So this is F 22 over here on the right and this is F 1.4. And you can see the difference just by looking at it how much more light comes through. It's pretty amazing right? Now what effect does this have on your image? This is an example of a very small or a very wide F stop. So a very wide aperture. I think I took this shot at about F 2.8 or so. It's a macro photograph so you're not seeing, you're seeing a pretty extreme version of F stops. This is very close up and the closer that you are to a subject, the shallower your depth of field. So that's just a rule to remember the closer that you are, the shallower the depth of field. That's a good rule to remember. Now you can see I was focused on my finger, my middle finger here and you can see that by the time we move forward to my pointer finger and we move back to my pinky, things are totally out of focus. And actually you can even see the back end of my middle finger is out of focus but the front end is in focus. So that is a razor thin field of focus. My camera is right here, my hand is right here and the field of focus is literally just like right there, really small. Now in the next photograph I decided to take a little bit of a deeper field of focus. So I think I move things up here to F 11 or so. And again we've got the camera, that's a really bad diagram. I've got my hand but this time the field of focus is almost my entire hand. So you can see that it kind of falls out as we're moving past my ring finger here. It starts to fall out a little bit and it also starts to fall out on the front end of my ring finger but you can see here now that the field of focus is much deeper. And this is not, this is a purely a vertical surface. It's a two dimensional surface and actually it's three dimensional if you include this little space in the middle here. This is the actual depth part of the depth of field. But it's just a plane that is going on forever and ever to the left and right and up and down so the horizontal and the vertical axes. But it's not crooked. So it's not like parts of this are, it's not like this for example. It's perpendicular, sorry it's parallel. So here's your sensor or your film. It's parallel to your film. It's not sort of crooked to it in some way. You can affect this with some sorts of tools that you can use for sort of trick photography but generally your depth of field is always going to be parallel to your sensor or your film and it's going to stay that way and it's going to then adjust in depth according to your f-stop. So how does this work? Good question. Well here's our lens. Here's our camera and maybe we'll put a person in front of that. So here we go and they've got maybe a little bush in front of them that we're shooting across and maybe they're standing in front of a house over here and maybe there's another tree over here for example. So you're choosing maybe a 50 millimeter lens that's going to shoot kind of photograph, it's going to kind of look like this right here from above and your focus point is on the face of the person right here. So this is your focus point. Now your focus according if you have a f-stop of maybe like f5.6 which is kind of a very common f-stop is going to be one third in front of the subject and two thirds behind. You're going to have a little bit more space behind and then in front until you get up to higher, until you get to longer lenses and then it evens out to 50-50 but with slightly wider angle lenses it's going to be around one third to two thirds. So that means in front of the subject you might have 30 centimeters of focused area and behind them you'll have about 60 centimeters. Together that's 90 and 30 is one third of 90 and 60 is two thirds of 90. So that's how that would work and as you increase so if you were to move up to f11 this one third to third relationship would stay the same but the lines that would define that would move back and forward. So it would move forward by one third and it would move back by two thirds and it would the focus with the focus point staying here on the face of your subject as long as they're not moving. Things that affect this are the length of your lens. So your zoom, so focal length, sometimes called your zoom. And you're also going to have your f-stop obviously is going to affect that also your distance to your subject. So the distance to the subject is really important in this equation. The closer that they move to you the shallower the depth of field and that has partially to do with this one third, two third relationship because as you're moving closer it's going to pancake down and it has a little bit to do with the way that your lens does that. But as that subject moves further away this is going to naturally deepen. So f5.6 looks totally different when the subject is three meters away from you as compared to them being 30 centimeters away from you. When they're 30 centimeters away from you you're going to have a really, really razor thin field of focus so it's going to be very shallow. And if they're farther away you're going to see more and more things are going to be in focus. So just another important note. What does this mean and what does this look like on a lens? Well a lot of times older lenses are going to have something that looks like this. One of my favorite things about using old lenses. You have this, here's your selector that tells you what f-stop you're at. So in this lens we're on f11. And here is your focus point sort of indicator. And right on this lens right now it's at probably about 1.5 meters. Now if you're at f11 which we're at right now, things between 1 meter and about 2 meters are going to be in focus. And if you move out to f16 it's going to be a little more and if you move out to f22 it's even a little bit more. So in some ways using these older lenses is actually almost easier to tell what's going to be in focus and what's not. It's partially why I use them and why I like them so much. Here is an example of macro photography and how extreme f-stops look and I'm sorry depth of field looks in macro photography. Macro photography just means you're taking photographs of small things or you're zooming in very closely on big things. It's photography that's happening at close range. And here you can see I zoomed in on salt, I salt and pepper are our salt shaker, assistant helper, photographer, people. They show up in some of our videos. And you can see here I zoomed in on salt, I and I've taken a photograph and you can see what happens to light coming from the background. It's amazing. It's what I love about depth of field. You can see the light is just turning into these big huge chunks. You can see, you can even see them here. You got just one big little piece of orange, orange. And this collar is just like three, let's basically just like three dots of light. Whereas here you can see all the detail of that. It's a very fine detail. The background is thrown completely out of focus. So this is also an example of distance being important in your depth of field. How do you use this in daily photography? Well, here's an example of using it to isolate a subject. I use my depth of field to isolate subjects all the time. Here I'm at a concert and taking a photo of my friend Sam. And, you know, I just wanted to have him and not all the other stuff in the background in focus. You can also take a look at similar photos that are taken from a little bit further away. So here, this is kind of a focal length that I really like. It's around maybe about 150. And this was taken at 5.6. Here you can see that I wanted to have a background where you can see a little bit that they're in the city. And you can see that they're being filmed by this film crew here. But I didn't want necessarily want all that to be in focus because I wanted the photo to concentrate on them. So here you can see their faces really clearly. You can see that there is a guy walking in the background bikes and that they're on a street. But you can't see all the detail. And I like that. So that is something you can do with wider f-stops, with longer zooms where you're not really far away from them. So here I was maybe two meters away. This is also a very common setup for when you're shooting sports photography. A lot of, you know, just imagine if you was playing basketball right now or something. You'd have a really nice looking photograph from that. Here is an example of f-stops being used in landscape or your depth of field being used in landscape. I've got f11 turned on right now. And you can see that I've zoomed. Actually, I'm not focused at infinity. My focus point is probably maybe around like five meters or so. And at f11 that gives me everything between infinity and probably about, I don't know, maybe like one meter or something like that. So you can see that everything from here all the way back to the edge of the earth is totally in focus. And I really like that. That's one great f-stop. f11 is really great for shooting landscapes. One f-stop I would not use for shooting landscapes is f22. A lot of people think, wow, that'll give me really deep field of focus. But actually, just in f22, everything is out of focus. So I would just say it has to do with the way lenses work and just so just don't use f22 for landscapes. All right, so that was your lesson about depth of field and about aperture. You have more questions or you'd like to learn more, check out alversity.org.