rptv: are smaller screen sizes sharper

Discussion in 'Displays' started by Ted Lee, Dec 2, 2003.

  1. Ted Lee

    Ted Lee Lead Actor

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    hi all -

    does anyone know if screen size has an affect on picture quality?

    it seems to me that a larger screen has a greater chance of being less focused ... resulting in a less sharp picture?

    or are other factors involved, etc?

    thx,

    ted
     
  2. ChrisWiggles

    ChrisWiggles Producer

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    Well...

    A larger screen will mean all the weaknesses will be easier to see. It shouldn't really affect the focusing ability and such.

    So I guess, from a reference PQ standpoint, the gurus would go for slightly smaller screens. And it more has to do with the ratio of screen size to viewing distance than anything in terms of inches or anything. If you're further away, a bigger screen is desired.

    Also depends on resolution. Sure, HDTV looks GREAT blown up really big. OTA TV looks like CRAP blown up to 8-10 feet wide. DVD is somewhere inbetween depending on how it's processed, and right crappy that big.

    Anyway, assuming you're talking RPTV, it shouldn't really affect things that much, as the screen sizes you're talking are pretty small already. RPTVs by their short throw nature have more problems getting properly focused, and the color will be more uneven from side to side, as opposed to FP CRTs. IMO, it's easier to see the phosphor grain for perfect focus on a bigger screen than a small one. I'd wager it's the same for electron beam focus/astig.

    And BTW my experience is NOT with consumer RPTVs.
     
  3. Ted Lee

    Ted Lee Lead Actor

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    as always chris, thx. would you expound on your statement about rptv's short throw?

    do you mean the distance from the lens to the mirror, mirror to screen, or something else? i would have thought a shorter throw would be more "accurate"???
     
  4. Rick Jones

    Rick Jones Extra

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    I guess it depends who you are, if your willing to sacrfice a little bit of PQ for a more theater going expiernce(Which i am). Then get a bigger screen. Though i'v noticed with DVD and Hdtv the differences arn't much at all.
     
  5. ChrisWiggles

    ChrisWiggles Producer

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    Distance from projector to screen (obviously includes any mirrors).

    RPTVs use more extreme shorter throw distance than the FP iteration of the same projector(it's my understanding that RPTVs usually have different lenses as well). The tubes and lenses have to be angled in more severely, leading to more focus problems from center to borders, and from edge to edge(side to side). It's more difficult to get *perfect* focus on the whole screen. It's often discussed whether you want perfect focus in the center and sacrifice the sides more, or sorta pretty decent focus all over.

    The other thing is color shifting from side to side is more of a problem with RPTVs than FP CRTs again because of the shorter throw and more severe angling of the guns, which is one reason why FP CRT is usually a nudge better than the RP iteration of the same projector(in these regards). Also keep in mind I am talking all-in-one boxed RPTVs, and in mentioning Rear-projection loosely this is what I'm referring to, NOT just a FP used in a rear-projection setup, but an expressly boxed and sold RPTV.

    A FP used in a RP setup has no difference in terms of the minimized color problems and focus problems, except that the screen is totally different(the projector just being setup projecting onto the rear of a screen). These are not using the very short throws used in RPTVs, usually.

    I am in rick's camp, I like the bigger picture myself, to a point.

    Hopefully my explanation is clear, though I fear that I am using "unstandardized" terminology. If so, plz correct!

    Oh, and Keohi is a great source for RPTV stuff.
     
  6. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

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    Greetings

    Consider that what you are feeding the TV has a finite amount of resolution and detail. It just does not get more detail because you blow the image larger and larger.

    It's the same concept with photographs. How come a 4x6 photo looks better than the 40x60 photo?

    How come a 640x480 image does not look as good as a 2000x 2500 image on a large screen?

    If image clarity were the only and all important issue, then we would all be watching 20" TV sets.

    Regards
     
  7. Tim K

    Tim K Second Unit

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    Correct me if I am wrong, but isn't it true that in order to get true HD resolution (all 1080 lines) on an RPTV requires that the RPTV have 9" guns??? I think most RPTV's under 58" have 7" guns whereas a 65" will have 9" guns.

    If my recollection is correct, that would mean that the largest RPTV's are capable of better pictures on HD sources.
    (Of course it depends on the manufacturer and so forth, but in essence)

    The source material is the key to answering the question though. If you are talking about cable TV with all of its flaws and quality issues, as the screen size gets bigger the picture will look worse. If you blow up flaws...you see bigger flaws. If you are talking DVD, I don't think there will be a visible difference in PQ between a 53" and 65" RPTV. For HDTV, as I mentioned above, a 65" TV will actually get you the best resolution of an RPTV. Of course, your viewing distance also comes into play. If you sit 4ft from any rptv screen it will look like crap. Whereas if you sit 8ft away a 53" RPTV may look better than a 65". If you sit 18ft away a 65" may look better than a 53".

    So the answer is "it depends".
     
  8. ChrisWiggles

    ChrisWiggles Producer

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    Depends on the set. Just because it has a larger screen doesn't mean it will be using larger 8 or 9 in guns, though it is more likely if you're paying the big bucks.

    They should display the higher resolutions just fine, but you may get softening of the picture.
     
  9. Ted Lee

    Ted Lee Lead Actor

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    thx again guys. that pretty much clears it up for me. much appreciated!
     
  10. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

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    Greetings

    The 9 inch crts don't really do much more than 1400 lines out of the 1920 total anyway. They don't do anything near full 1920.

    Of course, most 1080i material is already limited to about 1440x1080 ... given the equipment limits of the professional cameras.

    regards
     

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