Hi, I'm going to show you how to draw a principal ray diagram and make deductions from it for the situation when an object is placed inside the focal point of a biconebex lens. So I've got this biconebex lens that has focal point on each side and I'm happening to place the object or the source of the light inside the focal point. So what happens when we do that? Of course, you can go to equations and make calculations as well, but it's also good to be able to visualize what happens using a principal ray diagram. So the first one I typically do is draw p-ray and the p-ray needs to be parallel to this line connecting these two dots. So I draw a ray coming off the top of the person's head. Of course, an infinite number of rays come off the top of the person's head. We're choosing the one that happens to go this direction. And instead of having two small refractions, we just draw one big refraction and show it going towards the focal point on the other side. That's what parallel rays do. If the rays come in, ray or rays come in parallel to the principal axis, then they converge to the focal point on the other side. That's the definition of the focal point. Okay, so there's that ray. And then I can also draw an f-ray. So f-ray goes through the focal point and comes out parallel. But if I were to follow that very literally, then I would have a ray going this way and that never hits the lens. So what you do for that, the situation when the object is inside the focal point for a bi-convex lens, is you line up the focal point and the source of light. And instead of going this way towards the focal point, I'm going to go away from the focal point. So as if it had come from the focal point, even though the light never went there. So I draw a line up like this. That's my f-ray. And then f-rays, coming from the focal point, go out parallel to what the principal axis. So I draw a horizontal line coming out from the lens. Okay. And then the third ray would go through the center of the lens. And so, and that one passes through more or less NMP. So I locate the very center of the lens and I pass through that. Like this, more or less NMP, the very slight deviation as it goes in and out. But basically straight. Okay. Now you may notice that this lens, in this particular situation, has not made the light rays converge to a single point where we can locate the image. The light rays, although the angles they make with respect to each other aren't quite as big. So they've been bent towards each other a bit. They haven't been bent enough in order to make it converge to a point on the other side. So instead of converging over here, what we do is imagine our self is an observer on this side, where would these three light rays appear to have originated from? And so I draw dotted lines backwards from where the rays appear to have originated from. Okay. So this isn't where the light went. It's where the outgoing rays appear to have come from. So the odd line for the p-ray and then for the center ray, I also draw a dotted line. Okay. And it looks like I did not too bad. So I have located the image for the top of the person's head. It will be right there and then extrapolating to the rest of the person's body. I would get something like this. Okay. And so what can I say about this image? So here's our image. We've located it. It is virtual because I have dotted lines going there where the light rays appear to have originated from to an observer over here rather than where the light rays actually converge. That makes it a virtual image. Looks like it is upright and it is bigger. Okay. So if you have a little bit vague, certainly if you want a precise magnification, you measure it compared the two and then see take the ratio of the image height to the object height and then you have your have a bit more exact magnification. By convention, this image distance is going to be negative. So if I measure the distance from the image to the center of the lens, I wouldn't just throw that in as the image distance. It is actually going to be a negative number by convention when you have this type of situation. Okay. So that's how you deal with an object inside the focal point for a bicone vex lens. Thanks for watching.