Binoculars

Binoculars are a magnifying device universally used by the United Nations Space Command. They're often equipped with a stand to keep the device steady.

Use
Binoculars are generally used to observe the battlefield, gather data and locate enemies. Marine sniper teams have spotters with binoculars to observe and locate targets for the sniper. The UNSC binoculars have a digital display, which shows the temperature, as well as the distance to the target.

MJOLNIR Armor
MJOLNIR Mk VI is the first armor to have Binocular system in-game, though it's been stated in the novels that the earlier versions had one as well. The armor's binoculars are a 3-4x scope set, linked to the helmet's visor. The MJOLNIR armor's binocular system featured in Halo 3 has the same radius as the one in Halo 2. The only difference is that it's more detailed and that it shows distance to the target.

Trivia

 * The Binocular prop appears frequently in Halo 2.
 * The Sangheili Combat Harness also has a binocular system. Otherwise similar to the MJOLNIR's binoculars, it has a slightly different visor shape.