This can be done by centering the binoculars over your weapon and using them as a scope. For this to work the weapon and binoculars must be aligned correctly.

When you have successfully completed the game veteran interviews with Sgt. John D. 'Bud' Hawk, Gordon Boulton and Sgt. Stan Markut will become unlocked.

At the chapter select screen, hold down select and press Right x2, Left x2, Square x2