There are 2 other ways to simulate this. 1, place turrets on the tips of each boom, with the normals aimed towards the centerpoint. Then, use a (proposed SCP) modification of the fire-beam sexp, which allows the weapon to be simply fired, but not at a target. The weapon is fired directly down its normal. Then, create a weapon with the desired effect, but a range so it terminates at the focal point and timed by mission events to fire just before the main gun fires. The problem there is that it restricts the firing of that weapon to be event trigger only. The 2nd is a bit trickier. It would use either a co-ordinate system in the weapon tables, or the turret info in the ships table (which would be better). It would render a certain weapon effect (visual only, no dammage) originating from the designated point co-ordinate (requires trial and error to get accurately) and terminating at the turret fire-point. There would need to be figures to indicate how soon prior to the main turret firing (or perhaps before the main beam-glow starts), the effect should begin. You'd also need to designate a mini beam-glow for each focusing weapon effect.
