German gunsights and shift+f1

[IceFire]

Your field of view doesn't change. The eye point does and you could argue that it does make visibility from those cockpits worse... But the actual field of view doesn't change by hitting Shift F1. Exception: Aircraft equipped with telescopic sights.

Practically speaking, since German and Japanese types had offset gun sights, you do need at least two views shifting the eye point between something neutral for flying and looking through the sight for shooting. In most other planes it just changes the eye point so you can see a different set of gauges/visibility out the back.