Focusing a spot light

- [Instructor] With the spotlight still selected, let's just set up it's basic exposure. We can do that from the Channel box or the Attribute Editor. In the Attribute Editor, it will be found in the Arnold section. So I can close Object Display and open up Arnold, and here's the Exposure. Set that to a value of 14. Remember, this is going to be daylight, so it needs to be very bright. Let's test the attributes to see how they work. Move the light over to the floor, in the corner.

With it still selected in the Channel box, set Translate X to 300, press tab to go to Translate Y, set that to -50, press tab and set Translate Z to 50 and press enter. Now, in the perspective view, with that light still selected, press the f key to frame it and let's get a rendering of this. Go into the Arnold menu and choose Render. If you don't see the perspective shape you may need to select it from the pull down list here.

So we can frame that up in the perspective view with the keyboard shortcuts. Let's start playing around with these attributes over here. In the Arnold section, we have a Radius attribute. That's the size of the light source. Currently it's a point light source, because it has a radius of 0. Let's increase that radius up to 10. It didn't' have much effect here, but what it does is it softens the illumination and the shadows.

We need to have a really large radius, in this case. Let's set it to a value of 100. Now we can see it's a bit softer. The effect we want to achieve here, once again, is a collimated beam, or parallel rays of light. The first step in that process is to have a cone angle of 0, or as near 0 as we can get. If we drag this slider all the way over, we can only go down to .006. I'll just set it to .01, and we have virtually no light in our rendering now.

That's because we have a very narrow cone angle and we've not yet defined a lens radius. The icon in the viewport has turned into an arrow. Let's play around with lens radius. Scroll down a bit, and we have lens radius, and that is literally the size of the lens. We need a large size, in this case. So let's set it to a value of 20 centimeters. Finally, in order to see this effect, we'll need to disable Normalize.

There we have it; it's parallel rays of light, or a collimated beam. It's a pretty good approximation of daylight. Now let's set it up so that we can control the size of the lens radius with the radius of the NURBS circle. To do that we'll select a lens first. You do that in the top view. Getting close. Select the NURB circle or lens object. In the channel box, select the makeNurbCircle input node.

Then open up the Connection Editor. Windows, General Editors, Connection Editor. On the left we should see makeNurbCircle1. We need to load the spotlight's shape node into the right side of the Connection Editor. To do that, let's open up the Outliner. From the toolbox, click on the Outliner button. In the Outliner, under Display, enable Shapes, and then scroll down.

We're looking for light_key_spot. Open that up and then select light_key_spotShape. The shape node's selected, then click on Reload Right, in the Connection Editor. To make the connection, on the left select radius, and scroll down to the very bottom, on the right, and select aiLensRadius. Now that connection's been made, the radius of the NURB circle is driving the lens radius of the spotlight.

We can turn the Outliner display back to no Shapes. Close the Outliner and the Connection Editor. Reselect the lens. And either in the Attribute Editor or the Channel box, we can go to the NURB circle node and play around with the radius. As we increase the radius in the attribute editor, we see that the collimated beam is becoming larger. Set the radius of the circle to 65 centimeters. Increasing the radius also reduces the total amount of illumination.

So let's go into the light parameters once again. Select the spotlight. In the lights shape node, increase the radius. Here it us; we'll set that to a value of 300. Now we've got really bright daylight. Now we're ready to focus the light. Let's look at the camera view. In the Arnold RenderView, click on the pull down list and choose cameraShape1. With that light still selected, go to the Channel box. Select Translate X and set that to a value of 260.

Press Tab. Translate Y, 72. Press Tab. Translate Z, 208. Press Tab. Rotation in X, -13. Press Tab. And rotate Y 58 degrees. Now we've got the light focused exactly where we want it in the shot. The position of the light needs to take a lens radius into account. We can see that if we select the light in the top view. With that light selected, let's move it in it's object space.

Double click on the Move tool. In the tool settings, set the Axis Orientation to Object. Close the tool settings and move the light object, in it's object Z axis. If we move the light back so that the circle intersects with the wall, we can see that it's cropping in the RenderView, and that's a shadow being cast by the wall. Although the light's pivot point is inside the room, parts of the lens are actually behind the wall.

So we just need to take the lens radius into account. That's another reason why it's a good idea to build a rig like this, so we have a visual indicator of the size of the lens. We can move that back with the Z key. Let's set the Roundness to a value of 0. Now we've got a square, as if it were a square window. Change up the color of the sun. Go up to the top and click on the color swatch and set the mode to RGB 0 to 1.0.

Set the green value to .962. Press Tab and set the blue value to .95 and press Enter. Now it's just got a little bit of orange to it. Finally, increase the quality by setting the Samples up to a value of 5. And that's how to use a spotlight to emulate natural daylight, specifically using the lens radius to create a collimated beam, or parallel rays of light.