The Fresnel Lens
I want to talk to you about this. This is a fraternal lens spelled F R E S E L Fresno but it's pronounced funnel. It is a lens that was created by a Frenchman Mr final and he did this many hundreds of years ago to help lighthouses built gigantic lenses that were highly efficient but not very heavy. And these lenses are now used all the time in photography, but specifically with constant lights because they are really amazing. And so what I want to do first is sort of talk to you about what final did to create this wacky shape here and why it is important. And so I have an animation that will sort of help you understand what final did to create this lens. Final discovered that there was a way to make a very large and heavy lens much thinner and lighter. He created his lens based on a simple principle. If a ray of light travels from a more dense medium, like glass through a less dense medium like air and back into the more dense medium and the boundaries on either side of the less dense ...
medium are parallel to each other. Then an interesting thing happens when a ray of light enters the less dense medium, it will get bent away from the angle of entry. But when it leaves, the less dense medium, it will get bent back to the same angle as it had When it entered. This means that a ray of light will enter and exit at the exact same angle and that means that you can cut a parallel sided hole in the lens and it won't change how the lens behaves and that's what for an L. Did He cut a parallel sided strip out of the middle of a lens and he realized if he could cut one strip, he could cut too and if he could cut to he could cut three. He just kept cutting parallel sided strips until he'd removed as much of the lens as possible. This meant that the lens was a lot lighter but it was also very weak. The solution was to move the pieces together to create a solid piece of glass. Once that was done for NELL had created a much thinner and lighter lens, but it still behaved exactly the same as the thick and large lens. Later, the lens was refined by simply removing one side and making that side flat. The lens still behaves the same way. It's just more efficient. All right. So you can see that that little animation mimics the shape of this lens and on the back side here, that's actually flat. We can't really see that. But that's flat on that side. And the cool thing is because this lens is so thin because of the less dense medium that was worthy, wasn't it? But the less dense medium means that instead of passing through a huge piece of glass that's essentially a big magnifying glass, it passes light passes through a very thin piece of glass but it behaves the same. And so you get these really amazing facts from a lens that is light and thin and highly efficient. So that's a lot of technical mumbo jumbo. Let's see what this thing can actually do. So Theresa is going to come out and what we're gonna do here is I am going to have you go back sort of in the center, Hannah, I'm gonna give you this lens so that I forgot to tell you I'm going to do that. So we're gonna do is I have a Fresnel lens on this force of 500. I'm gonna turn this guy on and here we go. So you can see behind Theresa we have this big circle and so of course this is a circular light. It's gonna have a circular pattern and the thing to note is the transition. This is the thing that's important. So we have a transition that starts over here and goes all the way to the hot spot and then transitions out. And that is a smooth transition. It's very, very uh soft. So it's a very soft smooth transition which means that I can move this light and play with the edge of that light to get some really interesting effects. The other thing that we can do with a final lens is we can zoom it in when we zoom it in. Notice that we get a really small focused light. So Teresa, I'm gonna have you step over here just for a second. So when Teresa steps out of the light, take two more steps left please. Um you'll see that over here. We still have that smooth transition area on that light. So it's just a shorter transition, but it's still a seamless transition. It's hard to see where that transition starts or stops. It's pretty amazing. So Theresa, we're gonna have you go back and be on your mark there again. So I'm gonna put this light on Theresa's face and I have it zoomed in as tight as possible. So this is uh projecting light right on Theresa's face. It's like a spotlight. Now we've also discovered that this uh Fornell lens not only has a smooth transition and an even distribution of light, but it gives us the most punch possible for our constant light. So we're getting all that light. Remember when we did the test to see which ones were brightest? All of them with the final were the brightest. So let's look at the quality of light that we get from this lens. So what we're gonna do here is we're going to zoom in really close to Teresa's face. Now we have a really sharp shadow here, we have really, really hard light. It's beautiful light but we have a hard shadow underneath Teresa's chin. So what we're gonna do next is we are going to zoom out the frontal. So we're going to zoom this guy out. So it is giving us even illumination over a much wider area and I want you to guess what it's going to happen. Don't zoom in yet. We're gonna guess what that does for the quality of light on Theresa's face, right down, scribble a note, do something. What's your guess? Let me show you what it does. So we go close to Teresa, nothing. The quality of light does not change. So the light is hard light. If we're zoomed out it's hard light if resumed in, it doesn't change. The only thing that changes is how much light is being distributed and the luminosity, how bright that light is these. For now lights are fantastic for covering large areas with an even distribution of light. And because the light is hard and beautiful, we can create some really amazing portraits. So again, let's go really tight on Theresa's face. You can see that by moving the light to the side. We can give some high contrast. This is going to be great for black and white photos. We could zoom it in to restrict where the light is falling. We can do all kinds of things to shape this light and we'll get hard light that is really beautiful to play with. We're gonna do some of that as we get into our later sessions. And so thank you so much Teresa what we're gonna do later and we're almost there. So we're gonna be creating all kinds of lighting setups and playing with different like modifiers to show you exactly how to take the principles that we've shown you and put them into practice to create stunning portraits. So we're gonna do that coming up next.