I'm trying to learn a little bit more about how huds in military planes are able to get their info projected onto "infinity" (whatever distance is enough, like 10 meters or so??) so that pilots don't have to refocus constantly on looking between the outside world and the information on the HUD. Consumer-grade huds available on cars doesn't care for this, which I think it's outrageously dangerous. Often this automobile huds have their focal length right at the windshield... So even with collimating lenses I don't quite get how is this achieved (note: I'm not a physics student, just a concerned mind)...
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This might help - How can a lens collimate an image instead of just a point of light? – mmesser314 Dec 12 '23 at 00:50
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So basically, a collimated image can be perceived as in focus at whatever distance the pilot looks at, since the rays are parallel, is that it? – Satamanster Dec 23 '23 at 18:36
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It is like looking at a very distant object. Light from each point on such an object are very near parallel. Objects outside the cockpit are typically distant, so the HUD is in focus at the same time they are. Also typical eyes are relaxed when focused at infinity. – mmesser314 Dec 23 '23 at 19:22