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Inverse Square Law and The Projection Of An Image

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  • 30-11-2016 4:56pm
    #1
    Malpaisian
    Registered Users Posts: 136 ✭✭


    I'm just curious. Can anyone tell me if the inverse square law applies to the relationship between the size of a projected image and the distance between the projector and the screen?
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    #2
    mikhail
    Registered Users Posts: 3,863 ✭✭✭mikhail


    No, it doesn't.

    A projector is a magnifying, inverting imaging system. It obeys the thin lens formula: 1/d1 + 1/d2 = 1/f.

    A system like that has magnification d2/d1, which is linear with increasing d2 - the distance to the screen.

    The inverse square law applies to the light after it's left the lens, but you're adjusting the system so it's in focus, so it's not what you want when you compare different systems in focus.


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    #3
    Bit cynical
    Registered Users Posts: 2,338 ✭✭✭Bit cynical


    A square law rather than an inverse square law applies. Double the distance and the area of the image is quadrupled; treble the distance and the area increases by a factor of 9 (because 3² = 9).


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    #4
    Malpaisian
    Registered Users Posts: 136 ✭✭Malpaisian


    Thanks guys!


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