Aperture and Depth of Field
Our next section is on aperature and this is the third part of the ISO and shutter speeds that we had talked about earlier. This is the third element for controlling light coming in the camera. So let's dive into it. So the aperture is the opening through which light travels, so how much light can get in through the lens. And it's a term that is commonly misused in the photography world, because people will look at your lens and they'll say, oh, what aperture lens do you have? And what they really meant to say is what's the maximum aperture to your lens. That's what photographers are obsessed about in many cases. And so in this particular example we have a 50 millimeter 1.4 lens and so this is the 1:1.4, which actually means one over 1. and this is describing how much light is coming in for this particular focal length. Now there is a physical device in the lens that opens and closes and so this is the f-stop diaphragm, there's a number of iris different terms that can be used for cont...
rolling how big or small it is. So there's kind of two separate ideas. One is what's the maximum aperture and then there's the one that opens and closes. So with the one that opens and closes, often known as the f-stop, it's the ratio of the focal length to the lens to the entrance pupil. It's how big the opening is, okay? And so this is one of the more important graphics you wanna remember in this class, because there's a lot of things in photography, we deal with a lot of fractions and numbers are the exact opposite of what you would expect. 22 is the larger of numbers, but it's the smaller opening. 1.4 is the smaller number, but it's the bigger of openings. And that's because these are all fraction numbers here as well. So let's take our lens and let's close it down. So as we change the aperture on our lenses we are reducing the amount of light. And with each one of these settings we're letting in half as much light. And as we go in the other direction we're letting in twice as much light as before. And it's not that big of difference as you visually see it right there, but that's the affect of letting in either twice or half as much light with each one of these settings. And so these settings are very important and you're gonna be working with these very closely in the world of photography according to what you're trying to do in a particular case. So if we go from a number like 5.6 to f/ we are opening up our aperture, because it's getting larger. And it's gonna let in twice as much light from 5.6 to four. When we go from 5.6 to f/8 we're stopping down and we're letting in half as much light. Now if you saw the previous two sections on ISO and shutter speeds you'll know something feels a little bit different here. We're not doubling numbers to get twice as much light. The numbers work on a different scale here and it's because of the way geometry works. And if you have a circle and you wanna have twice as much space in that circle you just need to make it a little bit bigger, because all that area around the outside adds in as much space as the whole inside of that circle. And so that's why there's a relatively small difference in visual size, but it is twice as much space difference and twice as much light that can get through. So these numbers are not as easy to memorize, but they are important that you get to know them and become very familiar with them, because you're gonna be working with these on a regular basis. So aperture, beyond controlling the amount of light, are also gonna control and have an impact on our depth of field, how much is in focus. So let's go ahead and take our aperture and open it up all the way to its maximum opening and you can see the photograph on the right is showing us our depth of field. We get to see how much is in focus. And so you can see right around that seven and 29 mark you got a couple of red hash lines, which indicate the front edge and the back edge of what is in focus. And so when you shoot with a 1.4 lens you tend to get very shallow depth of field. So let's go ahead and start changing this lens and change the photographs as well. And you'll notice that those hash marks move a little bit every time we change that aperture. And so at any one given aperture to the next it's not the biggest difference in the world, but it does tend to accumulate and make for a bigger difference from one end to the other. So as we're closing our aperture down to f/16 and we are getting greater depth of field and we're seeing more of our subject in focus from the front to the background. Now different lenses will have different maximum and minimum openings and so these numbers will change according to the lens that you have. And so if you don't like what your camera is doing it's not the camera, it's the lens that's doing this. And so you can choose different lenses that have different capabilities. So choosing the aperture gets to be a little big complicated, because there's a number of competing factors going on here. First off, there's the technical side of things where you're trying to let in more light or less light, oftentimes to balance out where the shutter speed is or maybe where the ISO is set. But on the other side of things the aesthetics. Do you want a lot of things to be in focus? Or do you want just a few things to be in focus? And something that we're not gonna get into in this class, but it is something I do go into in other more in-depth classes, is the maximum sharpness is different than maximum depth of field. Sharpness just deals with how sharp is one object. Depth of field deals with how much of the field is in focus. And lenses tend to be at their best, their optical best, towards the middle of the range. But the problem I have with that is a lot of the fun stuff with really shallow or really great depth of field is on the extremes. And so I am a person who uses all the apertures, because there's different reasons for it. And so you might be wondering, if you are brand new to photography, do you want everything in focus? Or do you only want a little bit in focus? And that would be a good beginner question, because it's not something we deal with with our own eyes and it depends on the story you're trying to tell. So let's look at some photos and go through reasons why I might have chosen one aperture versus another aperture. We're gonna start with 1.4, a very shallow depth of field. And so you can see the eye is in focus and just a bit of the face is in focus. And whatever is going on in that background you really have no idea what's going on. And so as a storyteller I'm able to have my viewer, which is all of you, really focus your eyes on a very particular place and other distracting elements in the background are all just blown into oblivion you might say in the blur. And so it's for narrowing in and showing a particular thing that's in focus. In this case I chosen 2.0 for a very different reason. I chose 2.0 because it let in a lot of light and it's obviously a very dark scene. And in this case depth of field is not really an issue at all. At 1.4, this might seem a little confusing, 1.4 things were very shallow depth of field and now the tree is in focus and the stars are in focus and last I checked those stars were a long way from that tree. And so I'm not getting shallow depth of field here, and that's because there's a couple of different things that affect depth of field and one of them is how close you are to your subject. In the previous photo there was a young child very close to the lens and you will get shallower depth of field there. In this case the tree is probably 30, 40, 50 feet away and I tend to get more depth of field there. And I'm choosing f/2 here primarily because I needed to let in a lot of light, not because it had shallow depth of field, which was the case with 1.4. And so in this case I chose 2. for a couple of different reasons. Number one, I like the lions, the background was kind of interesting, but I didn't want it to be too sharp and distracting of your attention. And so aesthetically I wanted it to be shallow depth of field, but also I was concerned about my shutter speed, 'cause I'm in one of those Land Rover vehicles and it's moving around, 'cause there's other people photographing in there. And they might be moving as well themselves. And so I wanted a shutter speed that was fast enough to stop that sort of action, which meant that I needed an aperture of 2. and as a bonus I got shallow depth of field, which is what I wanted. Now you'll find photographers are very fickle and right in the next moment they're gonna like, no, I want the trees sharp and focused in the background. And that's part of the great thing about photography, it's up to personal interpretation. What is the story that you are trying to tell? The next aperture, f/4. In this case I had some conflicting problems. Number one, I have a lot of people moving around and so I needed a fast enough shutter speed to stop their motion, but I also had people that were close to me and people that were further away from me and I wanted them all to be in focus. By choosing a wide angle lens, which tends to have more depth of field, and an aperture of f/4, which in theory doesn't have much depth of field, but with a wide angle lens f/4 focused at 15 or 20 feet away does give you a fair bit of depth of field. And so it's gonna be impossible to memorize this out of the gate without going out and getting some practice, because an experienced photographer will just look at a scene like this and go, I think I need this aperture. And somebody who's brand new to photography would, I have no idea. And so this is why you need to get out there and you need to practice. But once you start playing around with it it's pretty simple. Like if I said, it's 40 degrees out, would you know what type of clothes to wear? Is that hot or cold? Well, I suppose that depends on if you're Fahrenheit or Celsius. And so it depends on where you're getting that information you would immediately know, okay, well this is probably what will get me close to the mark and then you start making fine tune adjustments from there. At 5.6 is getting more to the middle of the range here and so it's not important to get super shallow depth of field, because they have a wall behind it and that wall is not gonna be out of focus, 'cause it's too close to where they are. I suppose I could've thrown the chairs more out of focus by shooting at 2.8. But this is also where lenses are a little bit sharper, in the 5.6, f/8, f/11 range. And so if there's not something else I'm particularly trying to do I'll probably generally leave it more towards the middle of the range. The sharpest aperture for most general lenses is gonna be f/8. There's a great famous old saying on how do you take a great photograph? F/8 and be there. It's just a nice, middle aperture that's gonna give you a sharp image from it. And so in this case this is another subject that I think is noteworthy in a particular way that you need to kind of remember. I talked about this in shutter speeds. There's a special type of subject you need to be aware of and that is a subject that doesn't move. When it comes to aperture you need to be aware of flat subjects or subjects that are essentially flat. This is definitely not flat, but it is essentially flat. Because the difference between what is closest and furthest from the camera isn't much more than a few inches. And so it's a relatively narrow area that we're focusing on and so by shooting this at f/22, which gives us greater depth of field, it's not gonna help this photo out in any way. In fact, at f/22 the camera is not quite as sharp as it is at f/8. And if I focus, or if I set the aperture to 1. I'm not gonna really blur out any of the other elements in here. And so this is a sensible place for that photograph to be. As I get to f/11, 16, and you're gonna notice I need more depth of field. There's subjects that are at further distances. The close up buildings are still pretty far away, but those other buildings in the background are very far away and this is a telephoto lens, which tends to have a little bit less depth of field, and so I'm choosing f/11 to get all of these buildings in pretty sharp focus. I changed to f/16 rather than f/11 in this case, because the subjects are closer to me. The closer something is to you the shallower depth of field you're likely to get, which means I need to stop down a little bit further to get that depth of field to keep everything in sharp focus. I don't mind stopping down to f/22, I prefer not to do it, because my lens is not as sharp here, but if I need to do it because I really want that foreground in focus, because I wanted you to see the textures on that mud in there, 'cause I think it's an interesting play of light in there, as well as the fortress in the background. I wanted your eyes to be able to roll over the whole photograph and have everything in focus. That was the type of story that I was trying to tell in this type of photograph. And so you're choosing apertures to determine what you want your image to look like and what you want your story to be. And so there is no rule as to where things need to be with the aperture, but you are often choosing the aperture also for other reasons. Like I needed to shoot with this shutter speed, it forced me into shooting with this aperture. But it is something that you definitely wanna make a deliberate choice on. Now I will mention, I don't have anything up on screen, but beyond these numbers there are also in between numbers. So you can go between eight and 11, but there's actually a nine and a 10 setting in there as well and that's perfectly fine setting those third stops if you're trying to split differences you might say.
So I shoot a lot of food at a restaurant, so darker lighting, but close up. So a lower aperture setting?
For a lower aperture you're gonna need that for the low light, correct. You're gonna need it for handheld, 'cause they probably don't allow you to put a tripod up on top of the table.
But what I get to think about when I'm thinking about food photography like that is am I photographing my plate of food like this or straight down? Because when I photograph a plate of food straight down it's a relatively flat subject. And that's a lot easier to do with a shallow depth of field, unless I wanna focus on one, the baked potato over here, but I want the other stuff in the background, the vegetables in the background to be blurry. So it kind of depends on do you want everything in focus or not? The easiest way to get everything is because you have a flat subject is to shoot straight down. But if you really wanna highlight a decorative cupcake or something like that, you put that closest to you, you get right in close on that, and all the water glass and the silverware in the background goes into a nice, soft, out of focus area.
All right, we have an online question, John. This is from Ted, who says, so again, how much does distance have to do with depth of field? And I'm presuming it's distance to whatever your subject matter is.
Right, and so we're trying to keep this relatively compact in this class here. And we can get carried away, because there is a rabbit hole. And so your depth of field is controlled by your aperture, your focal length, and the distance between you and your subject. And so all of those have an impact and to be honest with you, aperture probably has the least amount of impact on how much depth of field you're going to get. Telephoto lenses have shallow depth of field, wide angle lenses have great depth of field. When you get close to something you get shallower depth of field. As things are further away you get more depth of field. And the aperture is just kind of a third way, but it's the primary way that we're talking about, but it's kind of a third way of controlling how much is in focus. And so there's many variables in there. Now realize that just because you want something you may not get it. Is that a shock? (everyone laughs) You might say, well, I wanna shoot with this telephoto lens of this macro caterpillar right in front of me and I want everything in focus from here to everything in the background. Just 'cause you want it doesn't mean that you can get it. And so you may want shallow depth of field in some cases where you're using a wide angle lens and no, you're not gonna get it. We're dealing with the physics of optics, which goes into a whole 'nother rabbit hole, as I say. But this is enough to get you going for now.
Right, thank you. Oh, we do have one more, great.
Yes, and the question is what is the relationship between camera focus and depth of field? Because sometimes when you take pictures there are instructions, oh, you need to set your camera focus on infinity or on this specific setting. In everything you described it sounds like there is a correlation here between depth of field, aperture, and camera focus.
Right, and so the two of them are kind of confusing and some people are not really sure, because what we're talking about is how much is in focus. And from the camera's perspective it's gonna be like this, how much in the foreground and background, but getting that focusing point set is a great leading question, 'cause that's gonna be the next section we get to, but it's also very important. And it depends on the type of photograph. I hate to promote one of my other classes, but I have another class here that's the long version of this called the Fundamentals of Photography. And in that class, it's so fun, I show you out of focus photos and I have you judge why they're out of focus. And some cases it's because you didn't have enough depth of field, in some cases it's because you didn't focus in the right spot. And they'll have a different look to them and they'll have a different solution to fixing that type of problem. And so the first thing is what's the most important thing you wanna focus on? And then how many other things do you want in focus or close to being in focus from there.