As seen in the end of halo reach (lone wolf) your helmet gets cracked in gameplay and it desrupts noble six’s vision.
Since Emile carved a skull onto his helmet and master chiefs was cracked by locke, how come they can still see clearly through their visers?
Emile most likely is relying on various sensors and cameras in the armor to see instead of direct vision (like a VR headset if it’s generating an environment that matches the location where you actually are).
Chief’s vision would probably have been affected by the cracked helmet, but it may have been compensated for by the other visual systems still working like what I described for Emile.
The more simple but less interesting explanation for Chief would be that his vision was affected by the cracked visor, but they just didn’t put that in our view on screen, because it would have been obnoxious to deal with for the rest of the game.
Noble 6 was punched really, really hard.
A lot of Spartan helmet have little or even not viser at all. Sadly, the only explanation is that it’s a game and no every detail can be realistic