Is this always the case for the chief ray? Meaning, does any ray passing through the center of the lens continue outward in the same direction? If so, it seems like that would be an easier ray to trace, conceptually, than the parallel rays (although of course you would still have to trace at least one of them to compute an intersection). Or does this just happen in this particular case? Are there cases when the chief ray wouldn't behave like this?
I believe so. The ray doesn't change direction if it passes through the midpoint of the lens. That said, I think it would be better to trace both the parallel and focal ray then use the chief ray to make sure all 3 points intersect at the same point.