Depth of Field
All right, so the apertures control how much light they let in, but they also control the depth of field. So let's talk about depth of field here. Let's start with an aperture of 1.4. In this example we have very shallow depth of field. The red hash marks on the right hand side, that indicates the front edge and the back edge of what is in focus, and everything else on this yardstick is out of focus. Let's go ahead and stop our apertures down, and with each aperture setting down we get a little more depth of field. The depth of field grows in front and in back of that area that we focused at, which is right about the seven inch mark on that ruler. As we stop our aperture down, now we have much greater depth of field. Even though nothing else in the lens has changed other than just changing that aperture. The apertures that you're gonna be dealing with in most parts of photography is gonna be f1.4 to f22. Why are you going to choose one aperture over the other? What's the best one? Well...
technically, you could choose a small one to let in less light if you have too much light coming in your camera. If you need to let in more light you can open it up to a smaller number like 1.4 or 2.0. But we're also gonna have the aesthetic reasons. For maximum depth of field we're gonna close it down to the f16, f22 range. If we want shallow depth of field, so our subject is in focus, but everything else is out of focus, then we're gonna need to open it up to 1.4 or 2.0. Let's take a look at some photos, and figure out why we use different apertures to take these photos. This photo was taken with a 1.4 aperture, and what I wanted to show you was just a little hint of something in sharp focus, but I wanted blur everything else, so that your eyes go exactly to what's sharp in focus. One of the ways, and we'll talk a little bit about this when we start getting into the composition section, is what're your eyes naturally wanna look at? We wanna look at things that are in focus. We don't wanna look at things that are out of focus, but every picture is a story and it's part of the story. It's just a less important part of that story. 2.0, and so in dark situations, if I wanted to shoot star shots at night, I would wanna a fast lens that lets in a lot of light, because I need to have a shutter speed that is fast enough to stop the star movement. So having a 2.0 aperture is something that you would very commonly use in a very dark environment. Little side note here. I don't know what the name of this tree is, but if I had to name it I would call it Pixar. Has anyone see the logo for Pixar with the lamp that's kinda looking around? 2.8, all right, so this is a really popular aperture to be shooting people in portraits, because you can have the person in focus, but other elements in the foreground or behind them out of focus so that your eyes go right to the subject. So, if you know where you wanna draw your viewers attention a 2.8 aperture can be very helpful in many cases. Closing down to f4. We don't have much depth of field here, but we have a little bit, so we can see one object that's in focus, and we can see something going on in the background and it's not totally, totally blurry, but we can see a little bit of what's going on, so it's a secondary subject. It's not quite as important as our main subject that is in focus. 5.6, here I don't need f22. I don't need a lot of depth of field, because it's a relatively flat subject. Pretty much everything is about the same distance from the camera. So shooting this at 1.4, if I had to, I could, but f5.6 is a nice middle place to be. These apertures are very, very sharp. You get very sharp photos from these middle apertures in general. Now, f8 depends on which lens you have, but this is kind of the middle of the range. Where in this case, this is a challenging photo to take, because the subjects are moving, so shutter speed wise you need to keep a relatively fast shutter to stop their motion, if you don't want too much blur. But you have subjects that are close to you and very far away from you. So you need lots of depth of field. Well, in this particular case, f8 was kinda that middle ground where it let in enough light that I could chose a fast shutter speed, or a fast enough shutter speed, but it also gave me enough depth of field that subjects in the foreground and subjects in the distance are both in focus. There is a famous old saying in photography, and I think it might've come from a National Geographic photographer where somebody asked this person, how do you take a great photo? He said, "f8 and be there." So, it's just a good middle aperture to use. When I get down to f I'm starting to want a little more depth of field. Which means I have subjects in the foreground and the background that really need to be held in focus. If it's not too close to the camera I can choose f11. That building on the left side is maybe 50 or 60 feet away. It's not right on top of me. Going down to f16. Okay, I'm really needing depth of field here, and so now I have subjects that are getting pretty close to the camera, as well as things that are pretty far away that I also wanna hold in focus. When I close down to f22 I'm getting desperate. I need lots of depth of field. This is in a slot canyon, and these walls are literally inches from the front lens. They're about eight to 10 inches from the lens of the camera. In that case, I need lots of depth of field, because it goes back down there a ways, and I want it all to be held in sharp focus. So, choosing the right aperture can be very important. You have to have kind of a little judge of what you're doing. There's another factor that we don't have a lot of time to get into, and that is that your lens determines a little bit of how much depth of field you're going to get. The wide angle lenses, those landscape lenses tend to give you more depth of field. Those telephoto lenses give you a shallower depth of field. So I encourage everyone at home or here in the studio to go home and just try different shots using your lens at different zoom settings and the same aperture to see how those images are going to look. With experience you will be able to walk into a situation, asses the scene, figure out what lens you're gonna use, and then you have to kind of figure out what aperture is appropriate for what you wanna do. But the first thing is knowing what you wanna do. Do you want shallow depth of field? Do you want lots of depth of field or something in between?
So I'm wondering, like how does this work, 'cause you'd think if you were letting in more light with a 1.4 f-stop more would be in focus, 'cause it's capturing more of it. Then how does it work that you have a greater depth of field with f22. I always get it confused, 'cause I always think, oh it's more wide open, so you're getting more of the image. How does that work?
Yeah, no, actually, all the light is passing through the lens, and by opening up a small opening it forces all the light through a small opening, and it changes the angle that it's coming in. I feel totally naked right now, because I don't have visuals to show you how this is working. Usually there's a graphic that we need to keep things nice and short here. So, it has to do with the changing of the angle rays in there. For the most part it just does it. You can't change it. It's just the way it is, and so by closing down those small apertures we do get more depth of field, and it comes with implications.
I always like to think about the pinhole camera, and how the pinhole is sort of the smallest, smallest that you could potentially have and everything's in focus.
Yeah, that's a good way to think about it.
Okay, so a couple of questions we have. Don Shanks says, on the example shot for 2.0, there was a well lit tree in the foreground, the moon in the background, and also we could see the faint stars. Could you explain how you expose that picture. He says, "Mine always comes out "with the moon washing everything else out."
Okay, so we're getting into a side topic. Of course, I like to throw a few extra tricks in there that we're not actually talking about. I was using a handheld light to illuminate the tree. All right, so it wasn't a flash, it was a flashlight. It was just a light. I just painted the tree with my handheld flashlight during about a 15 second exposure. The moon is completely overexposed, so it has no detail on it. I was just shooting with a shutter speed, an exposure that I determined through a little bit of practice right then and there. Going, I'll try this and I'll try that, try that. Love digital, being able to see those results right away. So that was just through a little trial and error. That's just a little bit of elbow grease, getting your workout back in, running and try it again till you get it right.
Thank you and just for clarification for Diane Kisner who says, "I'm a little confused still." Her lens says it's a 14 to 42 millimeter, and then it says one colon, 3.5 to 5.6.
Can you, in terms of f-stops, how does that relate?
Right, so zoom lenses will have an aperture for the wide angle end and an aperture for the telephoto end. It really depends on the lens. For instance, I have a lens here that is a zoom lens and it zooms form 18 to 55, and it's too far for the camera, but I'll read it off here for you. It says one colon, so that just means it's a fraction. 2.8-4, which means that the wide angle setting, the maximum aperture is 2.8. At the telephoto setting it's at four. In between, it's in between, it varies. There's a lot of these lenses. This is the way that you make the smallest, least expensive lenses. That's the easiest way to make a lens is that when it has a variable aperture on it. Some lenses, like this, this is a 24 to 70, but its maximum aperture is just 2.8. Now, it doesn't mean that's the only aperture, because we can close it down to 4 and 5.6 and so forth, but whether I'm at 24 or 70 it's at 2.8. With that lens that they're talking about you can get a lens like this. For instance, it sounds like they're on an Olympus or a Panasonic system, and so this is a 12 to 40, 2.8. So this is an available option for your camera if you want to let in more light, and have it be consistently fast at both the wide angle and the telephoto end, but it's bigger, it's heavier, and it's more money. So it's available, but it comes at a price.
Okay, this is from Yvonne. What would you choose first when you take a photo, ISO or aperture?
I would probably choose the aperture first to see where that put me in place of shutter speed, because if you remember going back to the ISO. Why do you raise the ISO? It's because you need a faster shutter speed. Don't raise your ISO until you know what shutter speed that you need. Now, as you get more experienced in the world of photography you may know going into a situation through experience, okay, I'm going back into this stadium, I know I need sixteen hundred, but for a new photographers, for people entering in new encounters I always like trying to teach, how can I get the best photos? ISO 100 and then you raise it up as need be from there. So ISO is usually philosophically, it's the last thing you wanna change.