Contrast Ratio on projectors

Discussion in 'Archived Threads 2001-2004' started by Leo Kerr, Jul 3, 2001.

  1. Leo Kerr

    Leo Kerr Screenwriter

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    How much is enough?
    Most projector resources will talk about a number of features and what they actually mean (Lumens, ANSI Lumens, real versus interpolated resolution... et cetera.)
    But none that I've seen actually talk about "what is a reasonable contrast ratio"?
    I know that the Digital Cinema people want 15 foot-Lamberts coming off of the screen, with an ANSI contrast ratio greater than or equal to 1000:1.
    I know that "full on/off" contrast ratios are usually in the neighborhood of twice the ANSI ratio.
    But for home theater use, in a dark environment, what is a minimum acceptable number? 200:1 (ANSI!)?
    Higher? Lower?
    This has been one of the bugbears in my persuit of a projector. I've seen a lot of good and very expensive projectors. But in my room, I don't need 5000 ANSI lumens. And I don't need a projector the size of a Volkswagon. And in my area, it seems very hard to find anyone demoing FPTV setups. (And I am morally opposed to RPTVs.)
    Leo Kerr
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  2. Nathan_H

    Nathan_H Stunt Coordinator

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    Projectorcentral.com has some interesting discussions of this topic. It sounds like even at 400:1, you'll have a tough time getting both white whites and black blacks, but that many people find that ratio acceptable. On the other hand, it sounds like more than 800:1 is overkill, when considering price/performance issues.
     
  3. Sean M

    Sean M Stunt Coordinator

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    Higher ANSI contrast ratios, particularly in digital projectors, lend the picture more snap and depth. Blacks will appear to be black in brightly lit, high contrast scenes. They are not, however, good indicators of overall black level. The overall black level of the projector is the best indicator of how the projectr will deal with low contrast, or dark scenes. Dark scenes are the torture test of any digital projector. If all you want to watch is Toy Story or other brightly lit material (sports comes to mind), then you don't need to worry about black level.
    The best way to determine the black level of a projector is to divide its Full On/Off Contrast ratio by its Lumen output. This will give you the minimum light output of a projector (a value I have heard referred to as the K of the projector). As an example, take the Sanyo XP-21N projector, it has a 2500 ANSI Lumen output and a 700:1 Full On/Off contrast ratio. This give it a k of 3.57. In other words, when displaying a full black screen, you will still get 3.57 lumens hitting the screen. By contrast, the new Plus Piano has a 600:1 contrast ratio with only 450 ANSI Lumens output. This yields a k of .75, or .75 lumens hitting the screen. In terms of reflected light, on a 80" wide screen, you get .14 Ft Lamberts with the Sanyo and .03 FtL with the Plus, a signifigant difference.
    This does not mean that you should look for a dim projector. A projector with a Full On/Off to ANSI ratio of somewhere around 1 should yield a very pleasing picture in terms of Black level, not CRT, but not far off from Film. Remember that the k value of a given projector must be converted to Foot Lamberts by dividing it into the area of the screen in question to get an idea of how good or bad it will be. 1000:1 contrast ratio from a 7000 ANSI Lumen projector on a twenty foot wide screen yields the same ANSI lumen floor as the Plus on an 80" wide screen. Let me know if that's too wordy and confusing and I will try to do a better job.
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    "Experience is the one thing you can't get for nothing." - Oscar Wilde
     
  4. Luis Gabriel Gerena

    Luis Gabriel Gerena Second Unit

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    I think something is wrong with your calculations....if it's ok then that means that my projector that has 400 lumens and 200:1 contrast should be delivering either 2 lumens or .5 depending on how the formula works.
    BTW m,ine is the Sony VPL-W400Q.
    Regards
     
  5. Sean M

    Sean M Stunt Coordinator

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    Luis, if the Full On/Off contrast of your projector is 200:1, with 400 ANSI lumens output, then you get 2 lumens minumum output (ANSI/Full On/Off). That would mean that on a 100" 16:9 diagnol screen (I used 4:3 in my original post, but your projector has a native 16:9 aspect ratio), you would get .09 FtL. The formula for FtL is (ANSI Lumens*Screen gain)/Screen Area (sq. ft.). For all of these examples I have treated screen gain as 1.3 (that's what happened to be in my spreadsheet at the time). Here they are at 1.0:
    Plus Piano - .02 FtL
    Sanyo XP-21N - .11 FtL
    Sony 400Q - .07 FtL (16:9)
    As you can see, the gain of the screen will have a significant effect on the Black level. Reducing the gain further, and/or increasing screen size will help this situation as well. You will note that the 10HT, which replaced your projector, increased light output markedly, while only marginally increasing contrast ratio (Full On/Off), resulting in what many have reported as poorer black levels. I hope this clears things up a bit.
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    "Experience is the one thing you can't get for nothing." - Oscar Wilde
     
  6. Stephen Dodds

    Stephen Dodds Second Unit

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    This, I believe, why the NEC LT150 has been so well received, and the modified Plus UP1100 clones.
    The NEC has 800 lumens and an 800:1 contrast ratio.
    Steve
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    Steve's Toys
     

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