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Topic: a bit technical question regarding retro reflective screens
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Joined: Jun 18, 2019
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I was wondering how much Gain you would get if the video projection beam was coming out towards a retro reflective screen nearly exactly from your eye position.
In my own home theatre the projector is on a tripod rather than mounted on a wall and the screen is a 120'' retroreflective one. I've always noticed when I crouch to grab something from the floor (the beer), the image gets so bright when my eye is amost in the same angle of incidence as the projection lens that the light dazzles me.

But the question of just how much Gain you get at that angle come to my head when I saw this:
https://www.youtube.com/watch?v=XPOgLt_73cY

To summarize the video it's a head-worn, very compact dual projector which directs the projection beam with special optics (a polarizer and QWP) to the screen and back to your eyes. So I'd guess you could expect very bright images even if the source LED wasn't very bright in this. Is 5.0 gain a reasonable estimate?
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Joined: Mar 28, 2005
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Not sure how I missed this, but all screen surfaces should list their gain structure as well as their half angle.

Basically every major manufacturer has dumped their retro reflective screen materials completely. They almost all used to have them, but projector technology has evolved since the turn of the century quite a bit. Especially in terms of brightness.

That said, any manufacturer making a glass beaded retro reflective screen should still have performed their own in-house measurements of how much gain the material provides.

This matters because if you want a 5.0 gain screen, then that's actually what you need to shop for, it's not something that should be assumed. The amount of reflectivity is going to vary from material to material. Some may sit around 2.5, others may go to 6.0. The higher the gain, the lower the quality will likely be overall. That is, you can't get even gain across the entire screen surface and common issues include hot-spotting, poor image brightness uniformity, speckling/shimmering, and very poor off axis viewing.

For these reasons, the big three (DaLite/Draper/Stewart) have all dropped their retro reflective screen surfaces.

This was a review of the Da-Lite high power 2.8 screen from a decade ago:
https://www.projectorcentral.com/da-lite_high_power_screen_review.htm
[Edited by AV_Integrated on Aug 26, 2019 at 8:39 AM]
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