Before we start designing systems in optic studio, let's take a moment to look at a typical relatively complex optical system, and understand what the components are. What I show you here is a camera, would be fairly typical for a prosumer or professional camera. It's a single lens reflex camera. That means, that there's a single imaging lens. It either sends the image to a display chip or up to the the eye of a user. This particular camera has rather, rudely been sawed completely in half. And that allows us to see a cross-section of the internal parts of the camera. And that cross-section view is actually fairly typical of what we'll look at in optical design code. So, what do we see? Well, we see lenses. These are the lenses that make up the main objective of the camera. Here's the front surface. And then there's some glass. You can see there's an internal boundary and a second glass that's been epoxied to the first. You can tell these are different glasses because you can see they look a little different elsewhere like these ones down here. You can definitely see that these are two different glasses. So, one of the things we've learned from this, is to use multiple glasses. Each lens is got a curvature. It's got some diameter. It's how big is the lens. It's made of a certain glass. It may have an air space to the next lens. And these are the kinds of descriptors we need to put into an optical design code to understand it. This camera also has a mirror here. This is on a mechanical actuator. So, it can flip out of the way to actually send the light to the detector chip or can come back here send the light up through a prism, through some more lenses and out to the user's eye. Right here, is an iris. This is like the iris of your eye, it opens and closes. This is the aperture stop of the camera. If you've ever used a camera, you know that this is a manual camera, like this. This is the way you control, among other things, how much light gets into the system. There's also knobs up here that you twist and it can change the distance between these elements. So, all of these are features that might be in a typical optical design. And they seem a little daunting. There's a lot of pieces there and lot of bits laid up in free space. So, how do we simplify this? Well, the first way we do that is we note, that essentially, all optical systems start with light coming off an object here, the center of the object, traveling in a straight line, we hit the center of these lenses. And by center, I mean, the rotational axis of symmetry. And that line continues right on to the image plane. So, this is going to be what we call the optical axis. It's a ruler or a number line, and we're going to lay out parts sequentially along that axis. In the case of these lenses, we notice that each lens can be specified by where it intersects the axis at its position, what's its radius of curvature and how big it is, and finally what glass comes after, what is it made of. In some cases, the material that comes after the surface might be air. And that's enough, as matter of fact, to pretty much lay out the system. And the assumption is, that we could just make a table, which starts with the front surface, goes through the whole system, includes the aperture stop, and finally gets to an image plane. And that will bound the optical system, will start from an object and with an image, and in between, will be a list of surfaces, specified as I described. So, how do we model such a system then is we imagine that the object is made up of a bunch of emitters that emit spherical waves. I've shown one of those here as a fan of rays, which represent the course, if they come from a point, a single spherical wave. And now, each ray, when it intersects a surface, is refracted by Snell's law, is traced all the way through the system, until it gets to the image. And then we can analyze things about that image from a convergence of rays at that image point. That's what the program will do for us. Now, here's a different configuration of that same optical system. The mirror, now we imagine, is down. The light is sent up through a prism and on through an eye, a cornea and onto a retina. Being able to analyze alternate configurations is an important part of optical design. Another classic alternate configuration would be if we change some of the spaces of these elements to refocus the system where it changes magnification. So, that's something we'll find in the program. You notice now that the optical access isn't really a straight line and it doesn't really go through the axis of rotational symmetry of this prism. But actually, these are just folds. We're just bending this axis, send it right here, gets right back to being on the axis of rotation of these lenses. So, we can put into such a program coordinate breaks and mirrors, and prisms. But generally, the idea that we hit lenses or other optical elements sequentially, and we can describe them sequentially from object up to image, will be the core of the program.
