I LOVE the idea of swapping out lenses by the way
I like this idea, however, I also think that the gun should be fun to shoot, and be fun to play against.
Because of this, I support the idea of the "sweet spot" to of the light beam at some certain range--not too close, and not too far.
This would make the gun a joy to shoot, as, depending on the range, the way the gunner shoots at enemies will differ. In the "sweet spot" the gunner will want to drag the beam across the enemy ship to stack lots of fire damage on as many components as possible.
Outside or inside of that effective range, the gunner will want to hold his aim on one component at a time in order to apply fire stacks effectively.
I'd also like to add that there should be a visual indicator on the light beam indicating the gun's "sweet spot" (maybe the beam is brighter, or a slightly different hue). This would help captains keep them within effective range, and gunners to be able to identify how the gun works in an intuitive manner. Furthermore, it will help enemy captains know what is going on, and help them realize where that gun is most deadly, and hopefully maneuver in/out of range.