[Skoob]

Some additional thoughts:

1) There's a scene early in Episode IV where troopers are boarding Leia's blockade runner, trying to move quickly, and one junior grade walks straight into a bulkhead, whacking his head hard. Having tried on a full-size helmet replica from the 501st, I can say that the visibility is very poor, as the field of view of those little transparent eyepieces is narrow. The helmets don't come with a transparent HUD like Iron Man's. We shouldn't be surprised to learn that hundreds if not thousands of troopers are killed every year from stupid falls off narrow battle station catwalks and gangplanks. (And if the Emperor landed on a heap of them at the end of his final plunge in Episode VI, they may have broken his fall, and he may have survived. Imagine the stink! Peuuuh.) Anyway, I agree: the most obvious explanation is that troopers have lousy aim because they can hardly see out of those helmets.

2) If the Empire is on its last legs, standards for recruitment and training may be lowered. Troopers may not know how to maintain and sight and operate their firearms properly. Our heroes must know how to adjust and test-fire their guns.

3) Troopers seem awkward and clumsy generally. Those suits of armor are hot and heavy. Troopers may simply be experienced and exhausted. If they have to move fast, they may even have trouble catching their breath and hyperventilate. If our heroes keep them running long enough, many may simply faint!

4) Trooper health may be affected by other things, like innoculations, or space-sickness, or bad food at the imperial cafeteria.

5) Troopers may also be sick of bad working conditions and intimidation by their commander and simply want the fighting to be over, so may pretend to fight by shooting in the enemy's general direction while actually rooting for the other side. Refusal to wear the helmet might be one indication of readiness to join the Rebellion.

Rgds