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Thread: ultra short throw video projectors and their "lenses"

  1. #1
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    Default ultra short throw video projectors and their "lenses"

    Has anybody here had a chance to work with these ultra short-throw video projectors? They all seem to follow the same design which is a regular lens followed with a curved mirror that enlarges the projection and shoots it back. https://www.youtube.com/results?sear...row+projectors
    Panasonic has also made some "ultra short throw lenses" for their high power projectors with swappable lenses and by the looks of it it just contains the same type of mirror inside. https://www.youtube.com/watch?v=_nlo2X518lY

    I'm curious what shape the mirror is and how it works if anyone knows. There are many DIY videos on youtube about making projections bigger by the use of a mirror but its just a regular flat mirror and all that does is increase the path length between the porjector and surface.

    First I would like to know if there's anything different about the lenses which come before the curved mirror.
    Second point of interest is the mirror itself. For DIY projects can anything like that be sourced from anywhere?
    And why is there a mirror instead of extra lenses to begin with? I know and experienced that fisheye lenses at such extreme values produce quite an amount of chromatic aberration but as far as I know mirrors reflect different wavelengths at different angles as well, so what is the benefit of using a mirror which every company seems to be using?

    PS. This is not for a laser related project but a hobby project using pico video projector plus accelerometer plus drone. Had good results with ordinary short throw pico projectors and fisheye lenses but need a bit wider projections still and with less chromatic aberration if possible so this is why I'm interested about these lens and mirrors inside the ultra short-throw projectors and what advantages it can have. So far only found a pico projector with such mirror by Sony but its not really that compact for my use case so probably need to mod one with my own mirror. I understand smaller picos are very dim for big projections but for my project it is enough if it is at least noticeable in pitch dark setting, don't need anything more than that.

    This is slightly unusual offtopic discussion but many of you seem rather tech savvy in many areas so hope so will find interest in this thing I'm working on.
    Last edited by mxandy; 08-28-2017 at 11:51.

  2. #2
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    Something like this?
    https://www.pinterest.com/pin/159244536798675898
    Or more like this?
    https://youtu.be/Wqq4-XC5f8U?t=193
    Metallic reflection does not have chromatic aberration. It can still have spherical though. That's a lot easier to precompensate in the image.
    I think the intermediate lenses may be doing that so you can get from a flat plane projection to a spherical collimated one.
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  3. #3
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    Not sure what you linked to is related because I didn't see the result (what was actually done).
    The USF (ultra short throw) projectors im talking about have a curved convex mirrors which allows to project very big from a very short distane compared to regular video projectors. The projection bounces off the mirror to a regular flat projection screen. Downside is the zoom is fixed size. What you linked seemed to use concave mirrors instead. And if I need a small mirror for a drone I don't think I can stuff a vacuum motor to use mylar so I need to find a ready mirror shaped like that or think of something else I think.

  4. #4
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    Concave mirror will do the same job as convex, it'll just flip the image. Easily corrected in settings/software.
    Frikkin Lasers
    http://www.frikkinlasers.co.uk

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  5. #5
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    Yes, good point, althoughwith concave mirror there will be a point where the projection beam can become an eye hazard.

    These are the off the shelf options I found but none seemed to fit the job. If you have any other idea let me know please.

    1) surveillance mirrors (half dome or quad dome), good but are too large to fit on a drone and used with a pico video projector
    2) wide angle circular street mirrors, not usable for the same reason
    3) small (few inches) wide angle mirror attachements for car and motorcycle side mirrors.
    Not sure what the problem is with these but the reflected projection is extremely blurry and can't be fixed. The magnification is about 20% so the issue is not theprojection being magnified too much. Maybe its the material used as reflector?

  6. #6
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    Mylar a form and a vacuum.....

  7. #7
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    Like I said that probably wont work as i cant put a vacuum on a drone

  8. #8
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    Like I said that probably wont work as i cant put a vacuum on a drone
    ... but you could "pre-fab" the concave foil-mirror with hardening/curing some epoxy on the back side and cut a piece to fit on your drone

    Viktor

  9. #9
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    VDX, you might be onto something here

    has anyone tried thermoforming mylar? That could be a more accurate and quicker way for prototyping various mirror shapes.
    any ideas why the mirrors I got blurred the reflections too much? What usually causes that? The mirrors look pretty smooth and reflective so my only guess is chrome reflective properties is to blame?

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