字幕表 動画を再生する 英語字幕をプリント DAN: All right. Everybody, welcome back to another week of exploring digital media. This is our second lecture here in the cinema. And this week we're going to be talking about framing composition and lens basics. And we'll actually tackle this in the reverse order today. We're going to start with lenses. So let's dive right in. We have two typical types of lenses. We have prime lenses and zoom lenses. And who wants to give me a quick definition? What's the difference? Yeah. AUDIENCE: A prime lens is a fixed focal length, and a zoom will have a range from 70 to 200 [INAUDIBLE].. DAN: OK. Yeah. So we have a fixed focal length on one, which means you can't zoom. Right? And a zoom lens or a variable focal length lens can zoom. Which means you can literally crank a ring on the lens and the image other enlarges or gets farther away. Right? All right. Great. Prime lenses. Construction is pretty simple. Inside we have a couple of lens element groups that when you turn the focus ring, some of them move, bring your image into focus or out of focus. And a zoom lens is a bit more complicated. As we look at this cross section here you've got a couple different lens groupings that move to either zoom your image in or zoom it out. And also change your focus. But I mean, look how complicated this thing is. Look how many lenses we have and how many moving parts there are. It's pretty crazy when you actually look at it. But why might we choose one or the other? Let's talk about some pros and cons. When would you want to have a simple prime lens or a zoom lens? Who's got some use cases for me? And zoom, feel free to-- if you're in the distant audience feel free to chime in as well. Yeah. AUDIENCE: I guess you would use a zoom lens if you want to be able to respond to the [INAUDIBLE].. DAN: OK. So when you want to respond quickly. OK so maybe you don't know what's going to happen. You're covering an event or and you need the versatility. Yeah. That makes sense. How about an argument for a prime lens? Yeah. AUDIENCE: When you want to isolate your subjects with a shallow depth of field. DAN: Oh. A shallow depth of field. OK. But can you not have a shallow depth of field on a zoom lens? AUDIENCE: You can if you zoom all the way up to 200. DAN: OK. AUDIENCE: [INAUDIBLE] aperture. DAN: So maybe there are some tricks to getting a shallow depth of field with the zoom lens. But maybe it's easier on the prime lens? Is that always the case? AUDIENCE: No. But [INAUDIBLE]. DAN: Not necessarily. So there's something in a zoom lens' construction that might make it easier to have a shallow depth of field. And we're going to talk more about what that means a little bit next week when we talk about exposure. Anybody have anything else? How about our zoom audience? Somebody give me a benefit of a prime lens over a zoom lens. Just open your mic up and start talking. Yeah. AUDIENCE: Say it again, Alex. DAN: Go ahead. AUDIENCE: I think maybe prime lenses let in more light basically. DAN: Let in more light. So prime lenses tend to be faster. Right? They actually let more light down the barrel of the lens, which means you get better low-light performance. All right. Great. AUDIENCE: Prime lenses are lighter. DAN: Prime lenses are lighter. All right. So the physicality of the lens is much smaller. Easier to move around. If you're going to carry a camera with you maybe you're taking a prime lens with you. Exactly. Right? So They're also-- they tend to be cheaper because the construction is simpler. We said faster. I like to put forced creativity here because with the zoom lens people stand in one place and will just zoom in or out to get the shot that they want. But it really forces you to get creative. You have to actually get closer to your subject or farther away. So I think that it's a really handy way as a starting photographer to challenge yourself to build a more complicated frame. They're lighter. There's less to break. So if you have to replace it, it's cheaper. And zoom lenses tend to be more expensive. They're slower as far as how much light comes down the barrel of the lens. But you do get that versatility. Right? If you're going to cover an event it's much easier to have a zoom lens so that you can snap in or snap out, depending on what's happening with the action. Or even if you don't want to carry a bunch of lenses with you. Let's say you're going out to shoot in nature and you just don't want to carry three lenses with you so that you have the options. A zoom lens will give all those to you. All right. So there are three categories that we define lenses in. Either a wide-angle lens. a normal lens, or a telephoto lens. Are the three typical ways that we define these. The three categories of lenses. And so let's first just think about what we see with our human eye. OK? So we have a peripheral vision of about 180 degrees which is pretty wide. But we can't focus on everything in our peripheral vision at once. The area that we actually can kind of focus on is called your foveal vision and it's about 40 degrees wide. Which is pretty narrow when you think about it. So a camera lens all have different fields of view. And they're typically marked with this marking over here that is something in millimeters. So the lens on screen here is a 50-millimeter lens and it has a field of view of 46 degrees. And I have a little asterisk down here that's on a full-frame 35-millimeter sensor. And we'll get to what that means in a second. And we measure this diagonally on the image. So diagonally across an image. And I do sneak pictures of my kids into my slides. From corner to corner we have a 46 degree of view. And that's just kind of interesting. It's not the reason that a normal lens is called-- or a 50-millimeter lens is a normal lens on a full-frame sensor. But it's just interesting that the degree of view that you see-- that you can pay attention to in any detail is similar to what a normal lens is. But really a normal lens defines the spatial relationships between objects, whether things are distorted and pushed farther away-- or compressed in on top of each other. A normal lens has the same properties of what your human eye sees. So again, a normal lens on a full-frame sensor is about 50-millimeter will just give you a typical spatial relationship between objects that you see down your lens. All right. So a telephoto lens is anything that's zoomed in. And I have pictured here prime lenses but certainly, zoom lenses or telephoto as well. This is an 85-millimeter lens, which has a field of view on a full-frame camera of about 28 degrees. So we're really narrowing down our field of view at this point. Whereas the wide-angle lens is the opposite. Right? So a 35-millimeter will give us about 63 degrees for the field of view. So which you might choose depends on what story you're going to go tell. How much of an area do you need to see? We've talked about what categories we have lenses in. Let's now play a game where we can actually look at images and describe what qualities we see in these. So we'll play a little game called wide, normal, or telephoto. All right. And how we play this is, I'm going to put up an image. And you're going to tell me, what do you think? Are we looking at a wide-angle, a normal, or a telephoto? So someone in the audience here. Yes. AUDIENCE: Wide. DAN: This is a wide-angle lens. Why do you say that? AUDIENCE: Because of the distortion with the ducks are closer to the front element of the lens. And you can see a lot of the background as well. DAN: OK. So I'm hearing that we have a lot of distortion in the lens. Right? So what is it that is distorted in this image? AUDIENCE: The beak and the duck's head because that's not how the ducks look. DAN: OK. So this isn't quite how a duck looks. Right? This is kind of a wild looking image. Right? And it's the distance in this image that's spread out. Right? Like we're elongating the ducks nose because we're so close to it. Right? And the distance behind it is really-- things spread out and get really far away. Even though these ducks aren't that big. Right? The trees presumably aren't as far away as they might seem in this image. Right? AUDIENCE: Right. DAN: Very good. And so this it's actually a very wide-angle lens. The 35-millimeter equivalent is 7.2 millimeters. So that's a very wide-angle lens. How about this one? Oh, crap. I left it up there. Spoiler. Why [? done with a ?] telephoto? I'll just stand over here. Somebody else. Ian, what do you think? AUDIENCE: I don't know. If you look at the width of the road and how it gets smaller and the background-- the difference between proximity and sort of the expansiveness of the space. I'd say it's probably a little bit wider. Maybe would be my guess. DAN: So you are correct. This is another very wide-angle lens. The equivalent is 11.9 millimeters. Another road. So similar to what we just looked at. Does this one feel different than the wide-angle lens we just saw? Anyone, AUDIENCE: Yes. DAN: Right. Yes, Dan. It does. It looks quite a bit different. Right? So instead of the road being wide up front as Ian said, and narrowing off very quickly, it's almost the same shape all the way down. And what is further away in the image feels much closer. Right? So we're probably looking at a-- AUDIENCE: [INAUDIBLE]. DAN: --or even a telephoto lens in this case. I jumped right over normal lens and went right to telephoto. So this image has a 135-millimeter lens on it. This image does. So this is actually a telephoto lens. And things-- we're looking at a compression of space. Whereas the wide-angle lens distorted and exaggerated distance. A telephoto lens does the opposite. It compresses space. How about this one?