Bitmap Source Module User's Manual

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When rays are emitted from the bitmap, we want them to go toward the optical system. To ensure
that this happens, we must provide a target to the Bitmap Source Module to use for aiming rays.
This is similar to importance sampling in TracePro. Switch back to TracePro to verify that front of the lens is at about z = 8mm and has a radius of about 50mm. Imagine a circular plane target at the front of the lens, with radius equal to 50mm and located z = 8mm. This is the plane from which rays in the source file will be launched. The Bitmap Source Module will trace rays from the bitmap to this target plane, and store the directions and locations of the rays in the source file at this plane.
Therefore it is important that the target plane not be embedded in any geometry. This is in contrast to importance sampling in TracePro, in which importance sampling targets are often embedded in
the model.