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Help needed with screen height

Discussion in 'Projectors, Screens & Video Processors' started by Mark Ward, Feb 8, 2003.

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  1. Mark Ward

    Mark Ward
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    I'm buying a 10ft (3m) 4:3 motorised screen from Roland.

    At what height should I have it?

    I've been reading various articles including Snaggs projector reference, Dolby Labs advice etc. but I really can't work out what the optimum height should be for my screen

    The Room
    42ft X 20ft x 18ft(Pitched).
    Seating position will be between 14ft-16ft (main seats) and 26ft. I'm using chairs & sofas not cinema seating so positioning is fairly flexible.

    Although I've had my first PJ (Barco BG801) for a while I've had VERY little time to play with it and I'm not yet familiar with setting it up. I will be getting an 808 as soon as I can afford it.

    If possible I want to use the top part of the screen for 16:9 so that the drop changes for 4:3 viewing (I next to never watch 4:3, only for really old movies).

    One article said the bottom of the screen should be at least 4ft from the ground. I've read loads on the optimum viewing angle width ways but can't find anything conclusive on height.

    Thanks for any input,

    Mark.
     
  2. Rob.Screene

    Rob.Screene
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    When positioning my screen, I remember Roland suggested your seated eyeline should meet the 2/3 of the way down the screen.

    I'm sure he'll know best.

    4:3 tv material on a large 16:9 projection screen is wierd enough compared to properly framed 16:9 films, am I getting you right in that you want 4:3 to be even taller than 16:9?

    regards,
    Rob.
     
  3. Messiah

    Messiah
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    Wouldn't it be better, for the small number of 4:3 material you are likely to watch, to keep the same height and have black bars either side. That way you can go for a proper 16:9 screen otherwise the majority of your viewing you're gonna have bars top and bottom (big ones).
     
  4. Mark Ward

    Mark Ward
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    This is exactly the sort of info I'm after, thanks!:)
    I was thinking it would be sensible to extend the screen further down for 4:3, yes. I wasn't aware I could shrink the image for 4:3 and have black bars at the side. I've literally had less than 2 hours looking at the CRT so far, but I need the screen in place to see what is possible.

    The main point I need to understand is.. Is it possible to use the top most part of the 4:3 screen for 16:9 viewing? or does the 16:9 image have to sit in the middle of the area that would be taken up by a 4:3 image?

    In other words:-
    Screen size will be

    Total white area of screen for 16:9 = 3000mm X 1687mm
    Total white ares of screen for 4:3 = 3000mm X 2250mm

    Can the top height of the screen be the same for both with just the drop altering?

    Sorry if I'm not getting this across well, I know what I mean I just don't seem so good at expressing it :)

    I would stop the screen at a different height for 16:9 so I shouldn't have "projected" black bars. I'm intending to run a black fabric matte the extact height of the screen's physical top black border so that I have a black top no matter what height I stop at. I'm not sure whether electric screens already have a top border always visible or only when extended the full length as I've only ever seen fixed screen before.

    I've said I'll buy the 4:3 from Roland and he offered me a cracking deal on it. 10ft 16:9 screens are very expensive anyway. This screen has motorised stops BTW.

    You've seen my room Neil (Messiah) so I'm sure you'll understand how small 8ft seems in it. The BG801s will struggle at this distance but it is only a stop on the way to a 9" PJ.

    Thanks for your input.

    Mark.
     
  5. Rob.Screene

    Rob.Screene
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    I think the real, physical limitation is the 4:3 raster area on the 3 CRT tubes.

    When projecting to a 16:9 screen, I think the Vsize setting is simply dropped about 33%. It does apparently waste phospor resolution and make the scanlines closer and more likely to overlap and bloom, which I think is why people say the 808's with average tubes can overlap scanlines and bloom at 960p height or more on 16:9 shaped screens whereas 960p height on 4:3 should be fine.

    I think I see that you are thinking to trying to maximise your projector phospor area usage which is sensible, but at the end of the day the source video is being scaled at least 1.5x if not 2x in both directions before being projected, so a little blurring will just make it appear more authentic (IMHO :cool: )

    I know of two ways to make 4:3 and 16:9 work on a CRT (i.e. not a fixel resolution panel). I'm assuming HTPC, but I think the more expensive scalers can work in the same way too:-

    a) Project a set resolution, say 1440x720 and have the software player add black bars left and right for 4:3, as Messiah suggested. So for 4:3 material, you are only projecting the image on to the middle 1080x720 pixel area. Still 1080 is a relatively clean 1.5 scaling multiplier of the 720 wide DVD source.

    With TheaterTek (and apparently ZoomPlayer, although I couldn't understand how to get it to when I tried it) you can set exactly a 1080x720 overlay and adjust x and y offset to move the image left and right within the real display area if you want. I think ZoomPlayer may also have limited orbit support to slowly move the image about around this to prevent burn-in within the set 4:3 area.

    b) Use two different Resolutions or Timings - multiple projector banks.
    You'd probably have to switch this manually. One you switch to for a 16:9 disc and one for 4:3 material.
    As you are then using two different adjustment banks on the Barco, you could set-up each exactly as you like, up to the safe limit near the edge of the phospor area (don't go further than that or the glass will apparently crack).

    I think the manual switching would be a pain, but I think TheaterTek at least copes with the odd resolution change during playback.

    The second downside I can think of is that the smaller image of the two will be wearing those phospors away a little quicker in a rectangle within the larger one!

    The third downside is that if you wanted to use different resolutions for NTSC/R1 DVD's and PAL/R2 DVD's which have different source heights (480 v.s. 576) and frame rates, then you'll end up having to set-up, select between 4 bank settings, which you'll also have to keep converged about every other month at least to keep the picture sharp.

    regards,
    Rob.
     
  6. Roland @ B4

    Roland @ B4
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    All excelent stuff and not a whole lot more to add.

    trying to shift the image via the adjustments of the projector will probably cause a bit too much stress. I would aim to have the 16x9 image = 1.78:1 (also bare in mind a lot of films are not 16x9 but letter boxed within. often 2.35:1) centred around the middle of the tube.

    also because the image is keystoned on the tube surface moving the image to the top of the screen will in effect move it to the bottom and hence, narrowest part of the phosphor. this will have several negative effects.
    More chance of tube burn
    Less bright
    Less sharp
    More strain on the electrics

    On the whole not a recomendation.
     
  7. Mark Ward

    Mark Ward
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    [Roland Said]
    I've now decided to settle for the centre part of the tube and have black bars at the sides for 4:3. I'll position the screen in such a way that the 16:9 image is the required height and use the stop(s) to prevent 4:3 being used in full.

    As for the required height... I'm still really confused where I should have this. I've read the eye level should be 2/3rds of the way down the picture, but on such a large screen it appear that the bottom of the 16:9 image would be very low indeed. If this is correct I will go with it.

    Having sat in a chair and trying to imagine (not very succesfully) where I'd expect the picture to be it's would be higher than that.

    In addition this formula leaves no chance of placing the subs in front L & R of the centre should I decide to try this positioning.

    I really don't want to get this wrong but setting up the PJ at various heights to try isn't really an option with my lack of experience.

    Thanks,

    Mark.
     
  8. Jeff

    Jeff
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    My screen is fairly high up, its only small at 72" diag 16:9 but the bottom of the screen is above eye height. I don't think its a problem, it really depends on the seating, my Ikea seats sort of recline a little as you lean into them and looking slightly upwards comes natural. Sit down relax imagine watching a film on the bid screen, where do you see the screen?
     
  9. Mark Ward

    Mark Ward
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    Well when I look at the wall and imagine a screen against it the bottom of the screen set for 16:9 would be around 80cm from the ground.

    I've mocked up a picture at home, I'll upload it later.

    This is fine with a blank screen but watching a 3 hour epic with it at what could turn out to be an uncorfortable height would be another matter.

    Thanks,

    Mark.
     
  10. Mark Ward

    Mark Ward
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    Here is where I see the screen going. This is nowhere near low enough for the 2/3rds formula recommended.

    This is an 11ft image on an off white dustsheet, the sheet wasn't perfectly flat either, but it gave me an idea that the colours would be adequate for me. Not as good as they were at 8ft but still pretty good.

    Viewing distance will be around 20ft.

    Any opinions,

    Mark.
     
  11. ReTrO

    ReTrO
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    I like your cloakroom Mark. I hope you get some curtains or blinds put in though!:D

    Good luck with the rest of the building and system.:smashin:
     
  12. JohnS

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    I think Jeffs got the right idea with image how your going to sit, when you sit do you rest your head against a headrest or does your neck support your head. At the veiwing distance your talking about I would of thought a little higher is the better option than too low....it just seems to feal more natural when veiwing a larger screen.

    Your welcome to come and veiw my 8 ft at a 14 ft veiwing distance if you think it might help, I'm not too far away from you.
     
  13. Mark Ward

    Mark Ward
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    That may be very helpful actually John.

    I'll PM you so we could see if we can find a convenient time/date that you may be free.

    Thank you :),

    Mark.
     
  14. Mark Ward

    Mark Ward
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    My thanks to John for allowing me to come and see his screen, setup. Now I have to worry about buying an HTPC to!!:D

    Nathan drove, who knew that Herne Bay is only 28 minutes from Maidstone. Must have been those damned roadworks on the A249 that slowed us up.:eek:

    I'm still thinking of the same position for my screen, this is quite a bit higher than conventional wisdom but having seen John's setup I think it'll work out OK.

    Thanks again John,

    Mark.
     
  15. JohnS

    JohnS
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    Hi Mark,

    No thanks needed, good to meet you ans Nathan.

    Regards
     
  16. bxd

    bxd
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    Mark,

    There are some quite useful articles regarding screens over at hometheatervillage.com. Have a look in the cinema source library.

    Brian
     
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