(Projector) How does the probe know?

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  • #138520

    asdfage wegagag
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    Hi Gurus>

    When measuring a projector screen, how does the probe know how bright it actually is in nits when it doesn’t know its distance/angle from the screen?

    #138524

    Vincent
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    Calibrite Display Pro HL on Amazon  
    Disclosure: As an Amazon Associate I earn from qualifying purchases.

    #138527

    asdfage wegagag
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    Thx vincent,  does that mean, as long as the circle is not outside of the screen, it will always read the correct brightness? Or do we have to input a calculated number somewhere.

    #138531

    Vincent
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    Did you read the PDF?

    #138532

    asdfage wegagag
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    I did read it vincent, but the nuances escape me.

    So I have the circle, but what happens if I tilt the meter a bit or if it’s very far back. It does not say anything about the distance, will the reading be correct at a distance?

    #138543

    Vincent
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    So I have the circle, but what happens if I tilt the meter a bit or if it’s very far back. It does not say anything about the distance, will the reading be correct at a distance?

    As you move the probe circle diameter changes… make sure patch size covers it. And if you don’t it will measure ofther light than your patch.

    If you tilt it check if it covers the patch: draw a schema & apply tigonometry: 2 angles in that drawing.

    • This reply was modified 11 months, 2 weeks ago by Vincent.
    #138547

    asdfage wegagag
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    Thanks for explaining that Vincent. If I have the circle, and now it’s an oval, the reading will still be correct?  Would off axis be more susceptible to other light that’s reflecting in the room?

    Would it help if I figure out the circle, then blacked out the light around it with some matte black material.  Or is measuring as is better take into account the complete system, which includes some of the light bouncing around.

    #138549

    Vincent
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    […]… make sure patch size covers it. And if you don’t it will measure ofther light than your patch.

    #138568

    asdfage wegagag
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    Vincent, Excuse my poor drawing of my last question. It involves patch size, but also reflections+ambient. Should the patch size be the whole screen or make it smaller, or should it be big, but then matte-d out on the sides.

    Would an oval be worse now because I’ve tilted it, and is it getting more stray light because the area is bigger than a circle would’ve been at perpendicular? Stray light from the rest of the image/patch/etc red line.  Blue line is the patch in the oval.

    Also, should the angle match where my head would be facing the screen to take into account any off axis response of the screen material?

    View post on imgur.com

    #138571

    Vincent
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    Vincent, Excuse my poor drawing of my last question. It involves patch size, but also reflections+ambient. Should the patch size be the whole screen or make it smaller, or should it be big, but then matte-d out on the sides.

    Patch bigger than viewing angle, do the maths, that’s all.

    Would an oval be worse now because I’ve tilted it, and is it getting more stray light because the area is bigger than a circle would’ve been at perpendicular? Stray light from the rest of the image/patch/etc red line.  Blue line is the patch in the oval.

    Also, should the angle match where my head would be facing the screen to take into account any off axis response of the screen material?

    Tilted it will get less light than in the direction of the normal vector from the wall  and your eyes will get less light too if they are in the same position… so what is the problem?

    Make sure you do not measure outside patch and taht’s all.

    • This reply was modified 11 months, 1 week ago by Vincent.
    #138592

    asdfage wegagag
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    Ok, thanks for the clarification Vincent. Sorry for my noober questions.

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