Lessons

Lesson Info

Focal Length

We're gonna be getting into one of my favorite aspects of this whole class. And that is dealing with the lens. And so obviously very critical factor. And with our interchangeable lenses when you change the lens, you're basically changing the camera. You have a whole new camera to work with. So let's get in and talk about the lens. Have a lot of things to talk about in here. And, lot of important sections. We'll start with focal length. And then we'll get into the depth of field parts later on. And we do have lots of quizzes for you out there. We're gonna be, in studio audience, we're gonna be awarding a lot of points today. So there's gonna be a big change in the point board here today I think. But it's a good chance for all of you at home to really test to see if you've really learned what we're teaching in this class. All right. Let's get started on the focal length. Now with lenses, there are some primary characteristics when I am purchasing or choosing a lens to use, generally numb...

er one is the angle of view. What am I gonna see from side to side? That's the main reason we're choosing one lens over the other. But we're also choosing a lens for its light gathering ability. If we work under low light conditions we're gonna need a particular type of lens. And with that aperture, the light gathering ability, it's also gonna determine how much depth of field we can get from the lens. And so that is the main reason we're gonna buy one lens or choose another lens for a particular purpose. But there is a lot of other things to consider. And I don't know that I would base a lens purchase on it but it's something I would wanna be aware of. And these go into the secondary characteristics. The first of these is image quality. That's right, image quality is actually a secondary consideration on many lenses for most people. But there's a lot of different things that go into image quality. It's not just simply a number or one attribute. And we're gonna take a look at all the different little things that go into image quality. Beyond that, there's a lot of physical things. The size and the weight of the lens. Does it use filters? What types of filters? All sorts of other things that are gonna separate an inexpensive lens from a very expensive lens. And we're gonna go through a lot of these to talk about what's important and what to pay attention to on these lenses. So when you take a look at a lens, lens on your camera perhaps, it's gonna have two really important numbers. Number one is the focal length. As an example it might be an 18 to 55. Or it might be a 50 millimeter lens. And the other really important number is the maximum aperture. This is how much light it can let in at its maximum opening. And that's really a standard for how good that lens is under low light conditions and how versatile it can be for a variety of types of reasons. And so we're gonna talk about both of these. But we're gonna separate 'em. And talk about one. And then well talk about the other. And then well get it all together and talk about both of them eventually. So first off, focal length. It's the distance from the nodal point to the image plane. And we don't have to, we're not gonna get too deep into the technical talk here. It's basically from the front of the lens to the back of the lens. And there's a little bit of play on that. It's not exactly that. But it's pretty close to that. And that's why a 50 millimeter lens is relatively small. And a 400 millimeter lens is relatively big. Is that, because that nodal point is out there further. Now we can't go very far in talking about lenses without refreshing a little bit about what we talked about on sensor size in the previous class. And that is because focal length and angle of view are very much related to sensor size. And so let me take you through another illustration to show it to you in a slightly different way. If we have a lens, and it really doesn't matter what lens it is, but any lens, lights gonna come through that lens, and an image is gonna be projected onto that sensor. The round image has just enough area to cover that sensor area, and that's how we get our image. We can take a copy of that lens, that exact same lens, and we can put it on a camera that has a smaller size sensor. What happens? Well light goes through the lens. And nothing changes about that. It produces the same size image circle. It's just that we have a smaller sensor in there. And so it's grabbing a slightly different, narrower angle of view. It's kind of the same picture but not quite. It's not exactly the same. And so we have the exact same lens but we have a different sensor and a different result from that. And so focal length is not the same thing as angle of view. It might have been better if we had decided in the photographic world to just call lenses by what angle of view you see from them. But that would vary according to what camera you put them on 'cause they have different size sensors. And so it gets little complicated 'cause there's different factors involved here. Now there are many companies like Nikon and Canon and Sony that make lenses that are specifically designed for the smaller framed sensors. And sometimes those lenses are a little bit less money. 'Cause they're a little bit simpler to design 'cause they don't have to design as big of image circle on it. And, they have special names. Canon called 'em EF-S. Nikon calls 'em, DX. And so forth. Now in some cases you're able to take those lenses and put them onto a full frame camera. It doesn't turn out too well because they don't produce a large enough image circle to cover the corners. And Nikon, you can put the smaller frame lenses on the full frame body, and it will allow you to shoot. And in some cases, it'll automatically just crop in, if you want, so that you don't see those vignetting dark corners. Now if you have a 24 megapixel camera that's gonna reduce you down to maybe 14 or 16 megapixels. So there's kind of a, not really a good thing to do. Canon said, you know, this is just a bad idea. And they produced a different mount so that you can't even mount those lenses onto the full frame Canon cameras. And so, you can technically do it in some cases but I wouldn't recommend it because you're not getting really good quality results from it. For a long time, the 50 millimeter lens had held kind of a special, notable place for photographers 'cause it's the normal lens. And a lot of times, I remember when my dad bought a camera, he was looking around to see which 50 millimeter lens he could get 'cause he wanted to get the fastest one for the money. And that's what cameras came with. 50 millimeter lenses. They were small. Practical. And not too expensive. So when you put a 50 millimeter lens on a full frame camera, you're gonna get what's considered a normal angle of view. And that's not to say that it's the same angle of view you see with your eyes. But as far as the perspective and size relationship of objects you're pointed at it's normal. It's about 40 degrees from side to side. If we take that same 50 millimeter lens and we put it on one of our 1.5 crop cameras, which there's lot of 'em out there, you're gonna get a little bit narrow angle of view of 27 degrees. If you have a 4/3rds camera, you put a 50 millimeter lens on that you're gonna get yourself a 20 degree angle of view. And so that is simply because we have smaller size sensors but the same size lens going back and forth. So nowadays, the normal lens is still the 50, but on the crop frame it's around a 35. And for the micro 4/3rds system, it's gonna be about a 25 millimeter lens. And what I have to admit is very unfair in the modern world, and I don't like things that are unfair, and that is is the fact that the gold standard for what we're gonna talk about in this class as well as everyone else out there is based on full frame cameras. And I have a question for our audience here. Just raise your hand, who owns a full frame camera? Raise your hand up. Okay. So we got one, two, three. We got four out of about 16 people. So one quarter of our audience owns full frame cameras. You guys are in the minority. All right? They can outvote you. They could just start saying that this crop frame camera, who has about a 1.5 crop frame camera? Okay. That's many more. That's almost the other half of the, double, about eight of them there. So far more people in my classes, and far more people out shooting photos, with this interchangeable lens cameras, have about a 1.5 crop frame sensor in their camera. That's the most common. But, 35 millimeter film was the most common. And that's why when photographers like myself, or someone who writes a book, or posts blog, or make a video, and they talk about angle of view and lenses, they're almost always talking about full frame gear. It's also what a lot of the professionals use who write those books and make those videos and write those blogs and so forth and so that's kind of the standard. And so it's, the onus is on you to kind of do that math to figure out, okay, he's talking about that, but I have this. And so you're gonna have to do that little math yourself. All right. So these are what we call equivalent focal length. They're gonna give you equivalent angles of view. So if we have three photographers with these three systems and three different lenses, they're gonna be taking basically the same photo when it comes to angle of view. And so that's gonna be with a wide angle lens. You wanna decent wide angle lens. You might need a 28. You might need a 17. Or you might need a 14. Depending on which system you're using. And so you always have to be relating things back to what's relevant to you with the system that you use. If you're looking for a pretty good telephoto lens it might be a 300. Or a 200. Or just a 150. All of these are gonna see about the same angle of view. Now there are two major categories of lenses. We have prime lenses. And zoom lenses. So prime 50 millimeter is your normal lens. And then as we get to lower numbers we have wide angle lenses, like a 35. And then eventually we start calling them ultra wides at about 20 millimeters. Telephotos. And then once we get to we throw the super in there and they get to call 'em super telephotos at this point. And there are a lot of zoom lenses because they are very practical and easy to use in a lot of cases. And they're gonna range the full gamete from ultra wide to super telephoto as well. Now a lot of people are always questioning well should I get a zoom lens or should I get a prime lens? What's best? Well, they both have their place and their purpose. I see zooms as incredibly versatile. You don't have to change lenses. You have all the intermediate focal lengths on them. When you're not totally sure about what you're going to be doing, and that's okay to be not sure about what you're doing, every time I go traveling, I don't know what I'm gonna be doing that day. That's the whole fun of traveling is it's gonna be something new. I could be shooting a portrait. Or a landscape. Or an agricultural shot. Or an architectural shot. You don't know what you're gonna be doing. And so zoom lenses are very, very practical. But when you really do know what you're doing, you're gonna be going to the basketball game, you're gonna be shooting a portrait in your studio, or at the park, and you know exactly the type of result that you wanna get and you have some control over the situation, that's when the prime lenses really get to be very, very handy. They're also really good when you just know that you wanna simplify things. There's a lot of times I'd been walking the streets of some foreign city and just have a 50 millimeter lens on. And my brain just starts, okay, I'm not gonna think about what I can or can't shoot with a 15 millimeter lens or a 400, my brain just starts focusing in on what can I do with what I have. And it's a fun way to narrow yourself down. Just say, let's do this one thing and let's do it right. And it's just good practice for photographers to limit themselves in that way.