Blender Cycles: How to make a Rainbow

Hi everybody. Today I'm going to show you how to make a rainbow with blender and cycles. I discussed this subject in this blenderartist thread.

I will take this scene from blendswap (made by @Prebeo Animation Studios) to test my stuff.

I want to include a rainbow in this scene, on the left hand side.

This is what I see when I open the file:

As you can see the background of the scene is a plane with a texture image. I will set my rainbow just before the background. (note about the background: As I want the render to be realistic, I have flipped the background image file. This is because of the rainbow must be in the opposite side of the sun. See the thread above for further details about a realistic rainbow by @CarlG)

This are the steps to create my rainbow mesh:

1. Set the cursor on the background plain (press Shift + S >> Cursor to Selected)

2. Add a circle mesh (Add >> Mesh >> Circle)

3. Rotate the circle 90 degrees along the X axis (press  R X 90)

4. Scale it to see the circle better (press S and drag your mouse)

5. Edit your circle and extrude it (press E, and Enter)

6. Scale you new vertexes inside the circle (press S and drag your mouse)

7. Grab your rainbow mesh just a bit in front of the background, along the Y axis.

8. Locate it in a realistic position, on the opposite side of the sun and in an angle around 42 degrees.

9. Add a Subsurf modifier to smooth the shape

Now it's time to setup your rainbow material. As I need to set my texture along the mesh, I will use UV unwraping. In particular I have unwraping my rainbow mesh with Follow Active Quads >> Even option. Previously you must select all your vertexes.

This is the node setup I have used:

And this the texture options. Pay attention to the texture mapping (go to Properties >> Texture Button >> Mapping ):

The rainbow is finished. If you render the scene you will get the following:

EDIT: I have modified the scene changing the position of the sun, to get a more realistic render (the sun must be in the opposite place to the rainbow).

Hope you enjoy it!

Bye