Basic questions about projectors

Discussion in 'Displays' started by Stephen Bort, Jul 19, 2004.

  1. Stephen Bort

    Stephen Bort Agent

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    Howdy, folks, have been nosing around here and projectorcentral, and still have a few questions that I hope you can answer for me.

    1) When they say that a projector runs at 36 db, is that a sound reading right next to the projector? Or from a set distance away? If a projector is four feet above your head, is the sound particularly annoying?

    2) I’m guessing that most people have their projectors set up so that some keystone correction is necessary. I’ve heard that the extreme is 30%, but what is considered a normal angle? Is 25% too much on an entry level projector? Is 15% too much?

    3) Is the only way to adjust the size of the image to move the projector further or closer to the screen? Is there a way to make a 90” projection and “squeeze” it down to 60” to increase resolution? (In other words, will an entry level ($1500 or so) projector look better the smaller the image gets?)

    Thanks!
     
  2. Christpher_S

    Christpher_S Stunt Coordinator

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    I'm very new to projectors but I've been reading constantly for a couple weeks now so I'll try question number 3.

    Most projectors seem to have an optical zoom to give you a range of image sizes for a given throw, or distance to the screen. Many I've been looking at have a range of 2 to 4
    feet difference in throw for a given image size. Check out the link below for an example.

    http://www.infocus.com/service/softw...site_region=1&

    To go a smaller image means that the projected size of the pixals end up being smaller and the image looks better. What I'm learning is that most of it comes down to viewing distance from the screen and image size. A smaller image, or viewing from farther away, have pretty much the same end result. With both, there is going to be a point where you can't no longer detect a difference in image quality. One thing to consider though is that your image will get brighter as you make the image smaller and it could get so bright as to be unpleasant with some projectors.

    Also remember that image quality also means the ability to accurately reproduce colors and black levels. I believe image size and viewing distance aren't going to have as much effect in these cases unless your going to extremes. Though brightness and contrast seem to be pretty tightly coupled.

    Anyone, feel free to correct me if I got something wrong.

    -Chris
     
  3. Stephen Bort

    Stephen Bort Agent

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    Thank for your reply. Anyone else?
     
  4. ChrisWiggles

    ChrisWiggles Producer

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    I don't exactly know what you mean by this, but this is not particularly the case. On/off contrast is not really correlated to lumen output.
     
  5. Christpher_S

    Christpher_S Stunt Coordinator

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    Would you mind explaining a little more about what a projector does differently to make one better at a particular viewing angle than another? I had the impression that viewing angle quality is determined almost entirely by screen gain and projector brightness. Maybe we mean different things by viewing angle? It sounds a little like you are using the term to mean the multiple of the screen size your seating distance is equal to. I'm not arguing with you, by the way. Just trying to understand what I've missed in my studies. [​IMG]


    Thanks,
    Chris
     
  6. ChrisWiggles

    ChrisWiggles Producer

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    Ah, you're right. Apologize for the confusion.

    You understood viewing angle to mean more the viewing cone, i.e. the angle off-center, which can be problematic with high-gain screens for instance.

    I mean the size of the angle from where you sit to the screen edges, because this ratio of screen size to seating distance is perceptually similar (brightness issues aside). We can't compare 80 inch wide screens as the same if you are sitting at 2x screen width, and I'm at 1.5x width. My viewing angle would be larger, so my perceived screen size would be larger. Viewing angle is just an easy way to speak in common terms.

    So when I mean that better projectors will support larger viewing angles, I mean that you can either sit closer, or run a larger screen, hence your "angle" of view to the screen is larger: it takes up more of your vision, and things are bigger, absolute screen size is not really the issue here. I run a relatively high-end CRT projector which throws a very smooth picture, so for me, even the highest end DLPs have a screen door that becomes objectionable at viewing distances much less than 2x screen width. Even lower resolution projectors mean that this is an artifact that I can see even at very small viewing angles (large distance to the screen). So a higher quality projector can not only resolve things better, but can also support much "larger" screen sizes in the sense of larger viewing angles.

    I hope that makes a little more sense without too much of my usual rambling [​IMG]
     

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