Andrew Kramer’s tutorial on Depth of Field for After Effects 7

[Andrew Kramer]

You need to “precompose” so the Lens Blur effects sees the “flattened” version of the gradient. If you don’t precompose the Lens Blur sees the layer color without the gradient effect.

The eye is essentially the on off switch however the data from a layer that isn’t visible is still available to other layers through effects in order to sample the values from the layer without actually seeing the layer.

So in the case of the Lens blur effect, the lens blur needs to use the gradient to figure out where the focal point is, but the visual need of the gradient isn’t needed.

Andrew