The HoloLens field of view issue has been preoccupying Microsoft for some time, and they have been exploring a number of solutions, which tend to show up in their patent filings.

As Microsoft writes:

This discussion relates to complementary augmented reality. An augmented reality experience can include both real world and computer-generated content. For example, head-mounted displays (HMDs) (e.g., HMD devices), such as optically see-through (OST) augmented reality glasses (e.g., OST displays), are capable of overlaying computer-generated spatially-registered content onto a real world scene.

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