DOF alpha channel weirdness

[Adam Trachtenberg]

Yes, unfortunately the built-in DOF effect does not work with alpha. There are some plugins that can handle alpha (ZBlur, Endophin), and there’s a workaround to produce a depth map that can be used for dof in post:

“apply a 100% white material to all your objects (and switch out any colour in objects with alpha maps to 100% white but leave the alpha channels unchanged), add in an omni light and make the light a child of your render camera. zero out the position and rotation values so it is centered on your render camera. set the omni light to no shadows, click the ambient illumination check box and then adjust the fall-off using the light fall-off parameters (use linear fall-off). render. because this method makes most sense when you are using alpha maps you will have to use best AA to avoid jagged edges on your alpha maps.

–Simon Wicker

P.S. Shademaster says no AA for depth pass

Place an Omni light at the camera position. Check Ambient Illumination and uncheck Diffuse and Specular. Turn off shadows and all other lights. Set the Falloff to Linear and the distance to the farthest thing away you want depth defined at 100% at. You can pull out the control handle on the light in the viewport interactively. Turn off all textures and render. To get depth maps where the foreground blurs just move the Omni Light to the center of focus and adjust the falloff. You can also play with Inverse Square and other falloffs to get more focused or different falloffs on the depth map. Whether they have any correlation to real lenses I am not sure..

HTH
Randy”

[Casey Baugess]

I know this is an old thread, but I have had this same problem. I found another workaround that seems to be working for me. If you just use object buffers, you can create the alpha channel in AE with luma mattes.