Using the Barndoor Light Filter (AiBarndoor)

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Barn doors are opaque moving panels attached to the sides of a light's opening. They are typically used in theatrical and film lighting for additional control over the shape of the light beam. This tutorial shows you how to use the Barndoor light filter and demonstrates various settings.

The Barndoor light filter introduces four barn door flaps. Each barn door flap has three parameters. The first two parameters position the two ends of the flap across the face of the light. The third parameter (Edge) controls the softness of the edge. This light filter can only be used with spot lights.

Barndoor light filter attributes

 

The following steps explain in more detail how to use barndoors.

 

  • Create a spot light and a polygon plane. Point the spotlight at the plane. Increase the cone angle so that you can see the effect of the light. Press 7 (Lighting>Use All Lights) and enable High-Quality Rendering, to better visualize the spotlight in the viewport.

 

  • In the attribute editor for the spotlight, scroll down to Arnold and under Light Filters, click on Add. A menu containing various Arnold light filters should appear. Click on Barndoor and then click Add. This will automatically make a connection between the spotlight and the Barndoor filter. You should now be able to see it in the Light Filter list. Double click on it to see its attributes in the attribute editor.

Create Ai Barndoor in Arnold attributes of Spotlight

 

  • Before we start adjusting some of the barn door flaps, create a Preset in the attribute editor for the barn door and call it Ai Barndoor_default. You will then be able to go back to the default preset values of the Ai Barndoor. This will make it easier for testing the various values. Create an IPR render of your render camera.

Create a default preset for the Ai Barndoor

 

  • Increase the Top Left value to 0.2. You should notice that the Top flap of the barn door is now clipping the effect of the spot light.

Top Left

 

  • Increase the Top Right to 0.2 to match the Top Left value. Notice that the barn door effect is more prominent. A value of 1.0 for both Top Left and Right would completely obscure the spotlight, and we would not see any visible light effect.

Top Right

 

  • Now that we are happy with the position of the Top flap, let us increase the Top Edge slightly to 0.05. Notice how it softens the effect of the top barn door. Now we can repeat this effect for the Bottom flap.

Top Edge

 

  • The bottom values, however, start from 1.0. To position them equally to the top flap reduce the Bottom Left and Bottom Right values to 0.8. Use the same value that we used for the Bottom edge, that we used for the Top Edge 0.05.

Bottom Left and Right

 

  • We now want to square off the Right edge of our spotlight. Repeat the above steps for the right barn door at the bottom.

Right Barndoor

 

  • We can control how much light appears on the left side of the screen using the left barn door. Increase the Left Top and Bottom values to 0.2. To pull the light in even more, we could increase these values even further. However, we do not want a hard edge. Instead, we can increase the Left Edge to 0.1. This has the effect of gently graduating the light as it falls off.

Increase the Left Edge to soften the left side of the light

 

  • Now that we are happy with how the Ai Barndoors look, we can save a Preset for it in the Attribute Editor, so that we can use it for future projects.

 

 

That concludes this tutorial on how to use the Ai Barndoor filter with a spotlight.

 

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