Depth of Field (DOF)
So depth of field is gonna be changed by, and adjusted, by changing the aperture on your lens. And so in this example, you can see at 1. we are getting very, very shallow depth of field. The red lines indicate the front edge and the back edge of focus. And so we have very shallow depth of field at this point. As we stop our lens down we're gonna get a bit more depth of field. It's not a huge difference. But it's a bit more with each step along the way. And each lens is gonna have it's own little setup as far as how much depth of field you get in here. And so this is for a 50 millimeter lens that you're seeing as this, in this example here. And the most amount of depth of field we'll be able to get this with particular lens is stop down at f22, where we have a very large great depth of field in this lens. Now, I know when I first learned about this and thought about it, it's like, you're pushing light through a smaller opening why do we get more depth of field? It doesn't make logical s...
ense. I don't see how that works. And so, it's a difficult thing to try to explain. But let me try to explain it with visuals. 'Cause I always use visuals. All right. So we're gonna simplify things here. And we have an object, a lens, and a sensor. As light travels from that little white spot through the lens onto our sensor, if our lens is on the right spot and all things are focused properly, we're gonna get a white spot on our sensor that properly indicates what that object is. Now, if we have the same lens and the same sensor but we move our object closer and it's not properly focused what happens is that it's designed to be focused at a different spot and our sensor is not there. And you'll notice on the sensor, we're getting this big cone of light. And what it is, is it's a big blob of out of focus light indicating that one spot that we were trying to sharply photograph. So if we can't move the lens of the object or the sensor what we can do is we can force the light through a smaller aperture. When we force that aperture to be smaller at the lens, the cone of light on the sensor becomes a little bit smaller. And if we take this to extremes, we take those apertures and we force it down really, really small the light hitting the sensor is gonna be just about the same size as it would be if it was in focus. And so we can force something that is out of focus to be pretty much in focus. In fact, this is the principal on which pinhole cameras work. They don't have any lenses. You poke a little pinhole in the camera. You let in a lot of light. Sometimes it takes hours of sunlight to get in there to get an image. And basically everything is in focus because it's coming through that really, really small opening. So, it's easy to get in focus images through really small openings. But that's really challenging 'cause you're not letting much light into the camera. And so we're gonna have a little bit of a conflict as we get into letting in more light versus sharply focused light. All right. So reviewing. We can open up the aperture to 1. to get shallow depth of field. We'll set it to 5.6 in this case for kind of a medium amount of depth of field. And well stop it down to the smallest opening on this lens here 22, to get our maximum depth of field. And so well be making these adjustments depending on what we photographers want to have in our photograph. Do we want everything in focus? Or do we wanna draw attention to one thing, have it in focus, and nothing else in focus? So depth of field is controlled by the aperture setting. Now to make things really fun and exciting and complicated, it's also gonna be affected by the focal length of the lens and the shooting distance. So there's actually three different things that are gonna throw you off in how much depth of field you're going to get. So as an example of depth of field controlled by focal length if we look at a 50 millimeter lens at f8, how much do we get in focus? When we shoot this exact same subject, yes it looks a little different, but when we shoot the same subject from the same distance, we're gonna get more depth of field with a 28 millimeter lens at f8. And so, if we look a the photo on the left pretty much everything is in sharp focus. Over on the right hand side, some of the pigeons in the foreground are not in focus because with a 50 millimeter lens we're not gonna get as much depth of field at f8. And so what aperture you need to accomplish something will vary from lens to lens depending on what you are doing. One general standard is true, and that is with wide lenses, you're gonna tend to get great depth of field. And with telephoto lenses you're gonna tend to get shallow depth of field. Now you can kind of fight this, and go upstream and try to get shallow depth of field with wide angle. And there's some things that you can barely do. And there's some things that you can do with telephoto lenses to stop 'em down to get everything in focus. But, just on their own, wide angle lenses tend to give you lots of things in focus. Telephoto lenses are gonna tend to blur out backgrounds and things that are not right where you focused. It's also affected by how close you are to your subject. And so in this case, I'm photographing subject from three, two, and one feet away. And what I'll do is I will magnify all the results so that you can see 'em all equally. And you will notice here how shallow the depth of field is when you get down to one foot. And this is gonna be something that is hugely important to anyone who is interested in getting into macro photography. Depth of field is gonna be a major challenge for the rest of your life if you're into macro-photography. There's a few solutions out there, and we're gonna talk about some of those as we go through the different sections of this class. But when you shoot macro lenses, depth of field is a challenge. You're gonna get shallow depth of field even stopping down to 22 in some cases. You're gonna get really shallow depth of field when you're using a macro lens. So it's controlled by aperture settings, focal length, and shooting distance. So, kind of going back to some of the talk we had before about lenses. All right? We have equivalent focal length lenses. We've looked at this slide before. These are all equivalent angles of view. They're the same aperture. But you're going to get different depth of field on them because they are using different lenses here. And so, depends on the lens you have. It depends on the aperture you have. And so in this example, I am shooting with the equivalent angle of view. They're all at 1.4. But if you look on the left side of each of those photographs, the area that's out of focus, you'll notice that it's more out of focus with the 50 millimeter 1.4. And that is because a 50 millimeter lens is a more telephoto lens and you're gonna get a shallower depth of field. If I stop that 50 millimeter lens down to f2, then it starts to be a little bit closer. And actually at 2.8, now all of these lenses are giving us a pretty similar depth of field. But I've had to change the aperture on these because they're different focal lengths because they're on different sensors. And so there's a lot of implications. You got this, so you end up with this, so you end up with that. And so, even though we're letting in the same amount of light we're getting a different amount of depth of field because they are different lenses. Doing this again with a 300, 200, and 150 lens. We've seen this before but it's important to see I think. Shooting a subject. How out of focus is that background going to be? Even though you're shooting at 5. on these three different systems, you're going to get a shallow depth of field on the full frame. And it's not because you're shooting with a full frame camera. It's because your lens is of a longer focal length. That's what really matters. And so, in some ways, depth of field is not affected by sensor size. Not directly. It's directly affected by the focal length of the lens that is actually on there. If you want that shallow depth of field with a 4/3rd sensor, yeah, just stick a 300 millimeter 5.6 lens on here, and you'll get that shallow depth of field. You're gonna get a different angle of view along with that. But depth of field is directly associated with the lens. Not necessarily the sensor. And if you want to get more depth of field we have to stop the 300 down to about f to make 'em look pretty similar to the 200 at f and the 150 at 5.6. And so, these combinations right here, they have the same aperture, so they have the same ability to work under low light conditions. If they had the same focal length, they would have the same depth of field. But because they have different focal lengths, they have different depth of field. Now I imagine at this point in the class, there's some people who are getting a little confused. And they might be just saying, okay, why don't you just give me a number. Tell me what number to set on my camera and I'll just leave it locked in there at the best aperture. Well there is a little bit more to talk about. And, I wanna show you a photo. And I want you to help judge sharpness. And so I want you to see what you think is the sharpest crops from this frame. And I'm gonna be showing you some crops from an image shot at 1.4, 2.8, 5.6, 11, and f22. And you'll see a crop from the middle of the frame. And the corner of the frame. And so, let's see, I need somebody in the audience here to volunteer as to what they think the sharpest aperture is. And so. Let's get the microphone to somebody who is, who would like to say what they think is the sharpest aperture. Who would like to volunteer an answer? What is the, what is the sharpest aperture to you?
It's like an eyesight test. But I think it's 11.
11 for you. Okay. What would be the worst?
1.4. Yeah. It looks pretty bad. Especially this one of the little lens down here. Now that looks bad because lenses tend to be sharper in the middle and less sharp to the corners. It's difficult to make a perfect lens. And lenses, all lenses, are imperfect in some degree. And they tend to get worse as you get over to the corner. But at 1.4 this lens is supposed to be perfect. But if there is a flaw in a lens you're going to see it pretty easily at 1.4. Now when you stop the aperture down, it's gonna give you a little bit more depth of field. And it's gonna disguise any sort of problems that that lens has. And when you stop it down to 2.8 and 5.6 and f11, it's gonna continue to disguise and hide those problems that the lens might have in any imperfection that it has. But if you go too far, we end up with another problem called diffraction. And so for the lenses that you own think about the range that you have in the apertures. And if it goes from 1.4 to 22, the sharpest aperture is somewhere near the middle. Maybe around 5.6. Now if you have a lens that goes from f down to let's say f the sharpest aperture is gonna be more around the f11 mark. Now this does vary from lens to lens. Depends on a few other peculiar things. But, in general, it's the middle of the range. And so you don't wanna shoot it wide open. You don't wanna shot it very closed. If you want the sharpness. The sharpest point on the lens. Now, clarify just for a moment. The sharpest part of the lens is different than depth of field. Depth of field is how much is in focus in front and behind the lens. I'm talking about just on a single plane, one object, how sharp is it? It varies according to what aperture you shoot it at. So, why are we gonna choose a specific aperture? Well there are technical reasons. We need to let in less light, so we stop the aperture down. We need to let in more light, so we're gonna open the aperture up. But sometimes it's for aesthetic reasons. We wanna maximize the depth of field to have a lot in focus. We can maximize the sharpness like we just talked about there. In the middle aperture range. Or we can go with shallow depth of field and really open up the aperture. And so those are the things that are gonna motivate us. And as you can see, when we have kind of artistic and technical things on opposite sides of the spectrum there's gonna be a battle where you technically need to do something but artistically you wanna do something different. And so that's where we have to play around with a lot of the controls of the camera to get the affect that we want. So let's start taking a look at some photos at different apertures. And see what kind of motivated me to shoot these types of pictures. All right. So 1.4. I don't often have a lens with me that goes down to 1.4. That's a fast lens. Usually a prime, well it's always prime lens that I know of. And so it's kind of limited in what it does. But it allows you to shoot with really shallow depth of field. And so I'm able to focus in on this persons hands. And you can really see it amongst everything else. And it's, your eyes are really down to it. So I'm doing this for artistic reasons. I don't technically have to do it in this particular case. Now, in this particular case, I do technically need to do it in some ways because it's really low light in here. And I'm trying to let some light in. And 1.4 is a really handy lens to have if you shoot under low light conditions. All right. Another example of I do want to shoot with shallow depth of field. I want your eyes to go to a particular part of the frame. And I can force your eyes to do that by putting that part in focus and leaving the other parts out of focus. In this case, low light conditions. And I'm trying to get enough light from the stars to register on the sensor. And so I'm choosing 2. I could have chosen a different aperture to have more depth of field but in this case I really didn't need more depth of field. I needed light gathering ability from this lens. Now, one of the things to note is that the tree is in focus and the stars in the background are in focus. Now I did just talk about 2. being fairly shallow depth of field and the distance from that tree to the stars is what I've known is a fairly large distance. All right. But it's not the actual distance that matters. It's the relative distance between the subjects. And that tree is relatively far away from me. And the stars, well, they're just a little bit farther away. And so when I focus on the tree, the stars are close enough to being in focus. And it partly has to do with the fact that this is a wide angle lens. And so that's the other factor. Things tend to be in focus with a wide angle lens when it's further away. It tends to be in focus. And so it doesn't really matter that I'm at f2. I'm still getting lots of depth of field because of those two other factors. Moving up to 2.8. Fairly fast aperture for a long lens. We're able to focus on our subject and blur the background out. It's not so blurry you can't tell where we are. But you get those kind of hints. And that soft background is a nice thing to have kind of as a secondary subject in your photograph. In a dark environment, it's really nice to have the 2.8 lens. And this is probably one of the biggest handicaps for people who have purchased kind of starter kit on cameras. You know that 18 to 55. Having a lens that gets down faster than 2. can be really beneficial in a lot of situations. And so, usually for people who have the 18 to and the 55 to 200 kit lens, I recommend getting a 50 1. or 35 f2. Something in a fast normal range so that you can shoot under low light conditions. Shooting at f4. It's the maximum aperture I have on some of my biggest lenses. And I'm able to get relatively shallow depth of field at f because I'm using a really long telephoto lens. And a long telephoto lens at f is gonna render shallow depth of field. But notice how much depth of field I get in this shot compared to the next one. Pretty much everything is in focus here. And the big difference is I'm using a wide angle lens. Wide angle lenses tend to have a lot of focus. And so, f4 means something very different for different types of lenses. And so, you gotta know a lot of these numbers to really get an understanding of what's going on in a particular photograph. 5.6 is the maximum aperture on some lenses. But in this case it's a macro lens. And it's just a couple stops in from it's maximum aperture at 2.8. And I'm choosing that for sharpness reasons. Because it just tends to be sharper here than 2.8. I don't need 22 'cause I don't want as many things in the background in focus. So I kind of want moderate depth of field. But I really wanted great sharpness. In this case I was wanting just a little bit more depth of field. An environmental portrait. I wanted the chairs. Didn't want 'em in perfect focus. But I wanted 'em in a little bit more focus than something wide open. In this case, kind of everything is far away from me. And so I don't need a lot of depth of field. And most lenses are gonna be really sharp at f8. There was a photographic saying, and I think it came from National Geographic, on how do you take a great photo. And the answer is, f8 and be there. And so f8 is just this good, neutral aperture. That's just really good for a lot of stuff. It's not gonna give you super shallow depth of field. Or maximum depth of field. But it's a nice in between aperture. And so if you wanna think about a really good aperture f8 is a nice prime one for that middle of the range. And so when you're photographing relatively flat subjects where you don't need a lot of depth of field, and going with shallow depth of field doesn't really give you any significant advantage, that middle f8, sometimes f11 range, is a good place to be. And so I shoot a lot of my photographs at f8, f11. And so, f11, I just need a little bit more depth of field. Long telephoto lens but there's great distance between the foreground and the background here. And so for close up photography here, you'll notice that a few of the weeds in the foreground are not tac sharp. F11 with a macro lens very close up, still doesn't give you very much depth of field. And the driving force on depth of field in this picture in my mind, is how close I am to the subject. Remember there's three different things. There's the aperture you choose. The lens you choose. And then how far away you are from your subject. And each one of those will play a strong or weak factor in how much depth of field you're going to get. When I start setting f you know I'm wanting more depth of field. I typically don't wanna go down there because there's a little bit less sharpness there. But if I need depth of field, I'm not afraid about making the steps necessary to make that happen. Even at 16 here, you can see the background is starting to go out of focus pretty quickly because this is a macro lens. We're very close to our subject. F22, I am getting desperate for more depth of field. I want things in the foreground in focus. I want things in the background in focus. But sometimes I'm choosing f22 for shutter speed reasons. I wanna slow that, I wanna let as little light as possible in through the aperture so I can set a really long shutter speed. So I can get down to 30 seconds. And so sometimes I'm doing it for depth of field. In this case it works for both things. I get my depth of field and my longer shutter speed. I get my cake and eat it too. And that's really nice. All right. Let's see if anybody can answer this question. With what type of subject does aperture, your depth of field, not matter? There is a type of subject. Let's get the microphone up here.
Something that's really flat or all in one plane.
Very good. I think she gets a bonus point. (laughing) And you know what, we're gonna give a bonus point to team b. (crowd cheering) 'Cause we got that right. And so if you are photographing something flat, which does happen from time to time. Your friend just painted a painting and they said, "Hey, could you document this? I wanna put it up on my website." And you go over there. And it's on a flat easel. You're gonna shoot that straight on. And you don't need depth of field for that. You set you aperture to the middle, which is often f8, f11, somewhere in there, and you're gonna get the sharpest setting on your particular lens. All right. It is time for your learning projects workbook. To go out and do your own depth of field test on your own lenses. And so I recommend doing this with your wide angle lenses, your normal, your telephotos. Do it a couple different cases. You're gonna need your tripod 'cause you wanna make sure that you can shoot at all different shutter speeds. And you're gonna probably need things in the foreground and in the background so that you can see how much depth of field you're gonna get in there. But I think that's a good thing to know because most experienced photographers when they walk into a situation, and they're gonna come up with a certain type of shot, I can, f11, 16, yeah, we're probably 11 or 16. They're probably just in their minds, they're narrowing it down to one or two options. And that's it. They're not going, well, it could be an f1.4 or maybe a 22. I don't know. They, you get to know these things with experience. And so the more you use your equipment, the more you do these little tests, the better you'll be at understanding what you need to do when you get the real situation where you might have a time crunch and there isn't a lot of time for playing around and oh, let's do some testing. No. Get in. Get your shot. Get done. And get out of there. And so, it's good to know your equipment ahead of time.