Luke's ocular device has a single objective (the part you see out of). But when we see what he sees, the view shows the double objective of common binoculars. Compare this to the view through the Hoth trooper's identical device, which shows a single rectangular image.
Rogue 2 radios to the rebel base that he found "them," even though he only sees Han. Luke might still be missing for all he knows. Unless by "them" he meant Han and the Tauntaun.
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