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Simple HUD optics design can be described with below image.

hud sample

(source : http://www.mikesflightdeck.com/hud/head_up_displays.html)

As you can see, if combiner and colimating lens(after fold mirror) aligned to the center, i think view point(eye pupil) can see colimating lens(after fold mirror) according to the re-reflecting rays by combiner(another expression mirror reflection).

explain image

Simple test with a couple Beam splitter as shown below image

bs1 bs2 bs3

As above, we can see colimating lens(small b.s) at the big b.s(combiner).

Here are my questions:

  1. To avoid those problems, should the ray have to be tilt(combiner, source ray's incident angle) obliquely to avoid re-reflecting ray. I think using this solution is a normal way. how can I remove above problem(re-reflecting ray) in HUD optics?

  2. it just idea, can I solve the problem with using polarization?(PBS or wave-plate)


Additional Example

i think it seems to look like this

enter image description here <- like this

enter image description here <- not like this

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  • $\begingroup$ What's wrong with apertures and baffles? $\endgroup$ – CuriousOne Jul 1 '15 at 2:05
  • $\begingroup$ @CuriousOne Case by my test, aperture is 10mm(no stop just B.S size)and no baffle(if using baffles, also seem together) $\endgroup$ – jun lee Jul 1 '15 at 4:19

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