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Lesson Info

Depth of Field

So let's talk about the Depth of Field that is created by the aperture. We're going to open up this aperture to 1. and this is an example of a 1.4 shot, and you can see these red hash marks over on the right side indicating the front edge and the back edge of focus. And as we stop our lens down at f/2, we're going to get a little bit more Depth of Field. And as we continue to stop our aperture down our Depth of Field continues to grow not by much on each individual change of the aperture but slowly it is getting larger and larger. You'll notice the numbers down at the bottom of the ruler are becoming more and more in focus. And so we're going to stop our Aperture all the way down to f/ so we get as much Depth of Field as possible. So this is the maximum amount of Depth of Field in this particular scenario. And when I first learned about this, I was really puzzled. Why does forcing light through a really small opening cause it to be more in-focus. And it doesn't make a lot of intuitive ...

sense, so let me try and explain it visually. So, we have our sensor. We're going to go with a really simple lens system here. And we have a white dot on this black disc. It's a really really small white dot. And if our lens is focused perfectly light travels through the lens onto the sensor and is represented by exactly a white dot on that sensor. Now, we have the same lens, the same sensor, but our subject is now a little bit closer to the lens and it's not quite focused correctly and that causes that white dot to become a big white blob on the sensor and the resulting photograph is this big white blob in the middle, so it's out of focus here. Now, normally if you said "I want to get this in focus", you'd just move the subject back a little bit, or you move the lens, or you move the sensor. But let's just say that you can't move anything. Alright? So we have the same subject, the same lens, same sensor but we're going to force the light through a smaller opening. That cone, that angle of view is different, and we now have a smaller blur on the sensor which means the resulting blur is a little bit less. And if we take this to extremes we force that light through an extremely small opening the resulting point of light on our sensor is going to be so small that it's going to look essentially the same as the single dot above that is in focus. So if we can stop our aperture down far enough everything will be in focus. And this is the principle which pinhole cameras work on. There's a whole thing called pinhole cameras, it's a shoebox in many cases, with just a pinhole put in there, and a piece of film, and if you leave it outside long enough, give it enough light, it'll create an image without a lens. The problem is that when you close your aperture down that far you're not letting in much light and you've got to let that aperture stay open for a long period of time, a long shutter speed in order to create an image. This is why f/22 gives more things in Depth of Field than f/1.4. And so just in review, 1. very shallow Depth of Field. We're focusing on the seven, and then we have a little bit in front and a little bit behind that's in focus. Notice the numbers at the bottom of that photo there, how out of focus there. They're so out of focus you can't read them at all. We stop our aperture down to 5.6. We're going to get more Depth of Field compared to the shot at 1. And that's going to stretch a little bit nearer and a little bit further away from our focusing point. And when we go to f/22, at least on this lens, that's the maximum Depth of Field that we can get, focused at exactly the same point. Our Depth of Field is going to stretch a little bit further in front and a little bit further behind. Depth of Field is clearly controlled by the aperture setting on your camera. However, Depth of Field gets a little bit more confusing because it is also controlled by the focal length of our lens If you remember back to our focal lengths those telephoto lenses having shallow Depth of Field. In this example, I'm shooting with a 50 mm lens at f/8 and I get a little bit of Depth of Field. Still at f/8 but with a different wide angle lens I get more Depth of Field and it's just because I'm using a wide angle lens. Wide angle lenses tend to have things more in focus than telephoto lenses. So something that you'll always be dealing with is wide angle lenses will give you a greater Depth of Field and telephoto lenses will give you a shallower Depth of Field. Examples, of a wide angle shot versus a telephoto shot. Now, it is possible to shoot wide-angle and shallow Depth of Field, and it's possible to shoot telephoto with lots of Depth of Field it's just the range that you're in is a little different of what you can do. So it is also controlled, Depth of Field, by how close you are to your subject. So in this case, I am still focused on the seven, but I was moving the camera one, two, and three feet away. I'm going to magnify the images so that we can see them all equally. And notice the Depth of Field of the one foot shot. Notice how shallow that Depth of Field is. We have just a few millimeters in focus in that case. This is going to be the constant challenge for anybody that is in macrophotography. So when you do macrophotography like this, you can see subjects in the background are way, way out of focus, and even just some of these little leaves and part of the stem that's a little bit closer are out of focus. You get very, very tiny Depth of Field when you are focused up very very close in macrophotography. So the three factors that are controlling the Depth of Field is your aperture setting, the focal length of the lens, and the shooting distance. So all of these things are controlling, and they're kind of pushing and pulling whether you have more Depth of Field or less Depth of Field. And it is time to talk about equivalence again because we have different sensors, different lenses, and the equivalence. So we have three lenses here: 50, 35, and 25. They all have the same aperture on them. They all have the same angle of view, but they do not have the same Depth of Field. So while these lenses do give you a similar angle of view they work under the same lighting conditions, they let in the same amount of light at the 1.4 aperture, your shutter speeds and apertures are going to end up being the same but the resulting photos are going to be a little bit different. So this is a concept that's recently come about that we call Equivalent Aperture. So let's pull up some photos here. So these photos, these three photos, were shot with three different cameras and three different lenses. And if you look in the background, there's a red bush in the background and you'll notice that the blurriness of that red bush in the background up in the upper left hand side is more out of focus with the 50 mm 1.4 lens. And that's because it's a 50 mm lens and over on the right it's a 25 mm lens. The lower the number, the more things tend to look in focus. And so what will happen is someone will say, "I have a 25 mm f/1.4 lens and it is the equivalent of a 50 mm 1.4 lens," and somebody from the equivalence police will jump in and they'll say "it's not the same!" Because, well, it's the same angle of view, it lets in the same amount of light for the same shutter speed and Aperture but it's not the same Depth of Field. It's a little different on the Depth of Field. So we have to stop the 50 mm down to f/ to look like the 35. So we have to actually stop the 50 down to 2. to this setting. So this is a Micro Four Thirds camera with a 25 mm lens. It's a 1.4 aperture and it has the equivalent aperture of 2.8 'cause the Depth of Field looks like a 2.8. And so it's a subtle distinction that nerdy photographers love to argue about. So just be aware, be forewarned, there's some landmines out there if you say "I have this lens and it's exactly the same." And so you're going to get a little bit more Depth of Field on your images if you're using the Micro Four Thirds system compared to full-frame, or if you're using a crop sensor like the 1.5 compared to the full frame. So let's look at it with a telephoto lens. 300, 200, and 150. These are all equivalent focal lengths. They're very very similar in their angle of view that they see. Here we are with an example from Micro Four Thirds a 1.5 crop in a full frame, they're all shot at 5.6 and you can clearly see that tree in the background has a different level of sharpness to it depending on which system we're using and it's because the 300 mm lens will render a shallower Depth of Field at 5. than a 150 lens will be at 5. and so if you like that shallow Depth of Field look you're at an advantage when you have a larger size sensor. We can stop the lens down to f/8, stop it down at f/11 and there it gets pretty similar. So the 150 lens, it is a 5. but it's kind of Depth of Field wise it has an equivalent aperture to f/11. But as far as letting in light, they both set at 5. you're gonna end up at the same shutter speeds. So once again these are equivalent focal lengths. They let in the same amount of light as far as the aperture of 1.4. So they have the low light ability. You can work in the same lighting environments with all three of these. Same focal length means they'll have the same Depth of Field and these do not have the same focal length so they will not have the same Depth of Field. It's just kind of different. How important is this? Well, it depends on how much you use different systems and how much you're going to be referring and talking to other people who use different systems. At this point, I know a lot of people are getting a little confused. I've actually had some people in my class just "what's the best aperture? Just tell me a number and I will set it, and we'll be done with it, and we can move onto the next section." Anyone feel like that in here? So what's the best aperture? And this is where I say "we're not done, I'm not giving you that number. We're going little deeper." There's one more thing that you need to know about and that has to do with image sharpness. So I did a little test shot and I wanted to see the sharpness difference between shooting at different apertures. And these subjects are all at the same distance so we're not worried about Depth of Field right now. We're just worried about image sharpness. So look at these pairs of images shot at different apertures, and try to judge which one is the sharpest and which one is the least sharp. If you had to choose one aperture that would give you the sharpest photos, take a look at those and let's do a hand raising by the whole group. Who would choose f/22? Who thinks that's the sharpest? Who thinks f/11 is the sharpest? Who thinks 5.6 is the sharpest? How about 2.8? How 'bout 1.4? Okay, so we have a lot of people around 5. and so what's going on here is there's two things going on The first thing is that lenses in general are sharpest in the middle of the frame. And so everything down here is always going to be a little less sharp than what's in the middle of the frame. Now, the one that is the worst, can we agree that this is terrible down here? This is terrible because one, it's off to the side of the frame. And second, we shot it at 1.4. Now, we do know, because we've already gone through this, is that you get more Depth of Field and so more will be in focus, foreground/background but that's not what we're talking about here. We're just talking about pure sharpness. Lenses are supposed to be perfectly sharp wide open. They're supposed to be. They're not, but they're supposed to be. And so a lens has got some imperfections and you're going to see them here, and as you stop the lens down you are going to hide those imperfections. It's going to mask any sort of little problems that it has with the sharpness because of that little bit of extra Depth of Field and so lenses wide open tend not to be very sharp. They're not as sharp as they are if you stop them down. Now, as you stop them down and you go too far what happens is that you're forcing light through a really tiny opening and you have a problem called diffraction and it scatters the light a little bit and it's not as sharp. And so what ends up happening is that apertures in the middle of the range are the sharpest. Now what exact aperture is that? Well it depends on the exact lens. If your lens goes from 1.4 to f/22, f/5.6 is about the middle of the range. Now it might be a 4, or it might be f/8, it depends on the exact lens. Now if your lens starts at f/4, it's no longer 5.6, it's maybe f/11 where it's the sharpest. And so what you need to do is just kind of click back and forth, see what the range is on your lens, and go towards the middle of that range, if you wanted the absolute sharpest setting for that particular aperture. So that does have an impact on the overall sharpness. Now, how much of this will you see in your final photograph? Depends on exactly which lens and how big a magnifier you get out to look at your images. So our apertures. Why are we going to choose a particular aperture on our lens? Well, one reason would be for technical reasons. Lighting reasons that we want to let in less light or we want to let in more light. The other reason would be aesthetics, we want to have a lot of things in focus, we want to have a very shallow Depth of Field, or we're just trying to maximize the sharpness. So let's take a look at some photos. 1.4, very very shallow Depth of Field. This is some Cuban cigars, and I'm choosing an aperture of 1. not for technical reasons, but for aesthetic reasons. I wanted a really shallow Depth of Field look in this shot so that the background is really, really blurry, and your eyes really go to the ends of the cigars and focuses your attention there. So you can use this as a storytelling tool where you want your viewers to look when you're shooting the photo or when they're looking at the photo. Let's drop this down to f/2.0. Completely different scenario here. And so I'm in another carpet shop and I'm shooting some carpets, and they're mostly flat. Now I'm shooting it at 2. because it's fairly dark in this particular room and this isn't perfect because you can notice this one in the foreground here. It's a little bit out of focus and the one over here on the left that's a little out of focus as well and this is just the best that I could do handheld. Then I'm choosing 2 not so much for aesthetics reasons but for technical reasons. I needed to let light in. So there's a variety of reasons why you're going to choose a particular aperture. 2.8, another handheld situation. I'm in a low light situation. I wanted to make sure the foreground was in focus so that you could see this. And I'm mostly choosing 2.8 just because it's dark in there. Going back, I think I'd kind of like to shoot it at 4, or 5.6, but I'd probably need a tripod which in this situation just was not possible. It was one of those fast moving situations. F/4, I'm getting a little bit more Depth of Field but because I'm so close in, it's still falling out of focus here because I'm so close in. And remember one of the things that affects Depth of Field is how close you are to your subject. 5.6, a little more middle of the range. This is where my lens, or at least this lens, is at it's sharpest. These are really sharp apertures, and I don't need more Depth of Field. Setting this lens to f/ does not help the situation in any way. What happens if we set it to f/22? Really small opening, we let in less light, we're going to get more diffraction. What happens if we set it to 1.4? Well the lens is not as sharp as it is at 5. so we're choosing the sharpest setting because we can because it's a very flat subject. So f/8, this is really not that different than the previous photo. This is certainly not a flat subject but relatively speaking this is a flat subject because it's so far away and the distance between from me and the closest thing and the furthest thing is not that big a difference. And so it is a relatively flat subject. I'm going to choose the sharpest aperture settings I can. When I get to f/11, I'm usually needing a bit more Depth of Field. I have subjects that are a little bit closer, subjects that are a little bit farther away, especially in relationship from one to the other. And so that's when I'm starting to add that Depth of Field. I don't have anything super close in front of the lens. There's nothing 10 feet in front of the lens in this case. Here, something is within 10 feet in front of the lens. This is relatively close. This is maybe 2, or 3 feet in front of the lens. And I want to hold focus from that foreground cross to the background as well, and that's what I'm stopping down to f/16. And then when I get it really extreme, when subject is super close to the lens, like over on the left side, this slot canyon is inches away from the front of the lens, and when I need to hold focus from there into the background is when I'm at f/22. And so sometimes I'm choosing aperture because that's the look that I want, and sometimes I'm kind of forced into do it and I need it for technical reasons. Alright here's a question for somebody. "With what type of subject does aperture not matter?" I'm going to see if we've got somebody who can answer this. Where does the aperture aesthetically not matter? I would think maybe landscape because it's so far off in the distance that more's going to be in focus. It's hard for me to say that's wrong. That wasn't really the answer I was looking for. Does anyone else have an answer? Pass the mic over. My guess would be architecture. Architecture? That might get a little closer to the right answer. The answer that I had Kenna, does the Internet want to chime in? Yes, there's always that delay, but ColoradoMel says "flat subject". Okay, so that's specifically what I was looking for. A flat subject. And so remember if we shoot something that's flat just imagine we're shooting the front of this giant TV screen, and our camera's out in front of it, we don't need any Depth of Field. Everything's the same distance relatively speaking from the camera. And so if you were talking about architecture as far as the front of a building that would be exactly right. And so, for instance, if you have a friend who does paintings, and they paint a picture and they said, "you're a photographer. Come over here and take a picture of this because I want to put it up on my website." That's a flat subject. And you don't need any Depth of Field and so that's when you start thinking about "okay what's the sharpest aperture on my lens?" Not where do I get the most Depth of Field. And so flat subjects are kind of special subjects when you get to shoot them because that gives you a little bit more freedom in where you get to set the aperture. So your next learning project is to do your own Depth of Field test. So once again there'll be an accompanied video so you can watch me doing Depth of Field test, but this will show you where you get the subject in the foreground and the background shooting different apertures and you get to see how much Depth of Field you get with a particular lens. Now there's some fun variables that you can add into this. You can run to the old test and do it on different lenses or you can just change exactly how close you are to your foreground subject. Because most good photographers are able to walk into a situation and say "yeah I think I'm going to need f/11 here," just because they have experience. They may have the app on their phone, but they don't need to pull out their phone they just know from experience, "with this lens standing over here, it looks like I'm probably at 2.8 is what I want to do." And so this becomes an immediate intrinsic thing. It'd be the analogy if somebody said, "it's 40 degrees outside," and you think about, "what do I need to wear when it's 40 degrees?" You immediately know, "well I'm probably going to want this shirt, maybe this coat, and maybe I'll take that hat." And when they say it's 70, it completely changes your outlook. And so this is one of the things that you want to be very familiar with, and able to make those quick decisions on.