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Distance from Screen:- Is as near as possible best?

Discussion in 'Projectors, Screens & Video Processors' started by Mark Ward, Apr 13, 2004.

  1. Mark Ward

    Mark Ward
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    OK, I'm taking the plunge this week and going for a DLP, I just can't hang my Barco BG801 CRT from the ceiling and it's time to move on.

    I've chosen the BenQ8700, though my question would really be the same for any PJ.

    On projectorcentral there's a distance calculator that says for my 3M wide screen size the PJ needs to be between 4.15M and 4.97M from the screen. I'd imagine that the nearer to 4.15M I can go the brighter the image will be. Am I best to try and get the PJ as close to the screen as possible? or are there other tradeoffs?

    Cheers,

    Mark.
     
  2. Gary Lightfoot

    Gary Lightfoot
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    The brightness should be the same regardless of where you place the projector as the light will be made to fit the screen fully anyway. You just use the lens to focus the light tighter when further away, so the same amount of light is striking the screen.

    The zoom allows a more flexible location of the projector and easier fine adjustment than a fixed lens. The difference in focal length shouldn't make much difference overall, though I'm sure RTFM or Gordon can explain the differences of full in/out zoom on image quality for us.

    What's your seating distance from the screen? You can't sit as close as you could with CRT due to screen door, so something like 5.5 to 6m away from the screen would be a nice place to start.

    Have you seen the Benq in action?

    Gary.
     
  3. theritz

    theritz
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    Mark,

    That's quite a big screen - about 10 ft wide ?..................... I'd like to see the benq (or any other projector...) firing at a screen that big before I'd buy it......... screen door could be an issue, but if you're seated > 1.5x screen width away you'd prob be ok as far as screen door is concerned - tho' if it was me I'd still want to see it in the flesh.

    As far as screen brightness is concerned you'd prob be ok, but as a general rule I'd consider 8' wide the limit for screen size - your room is cavernous, iirc, so you have different needs.

    As far as zoom is concerned, the only thing I'd be cautious about is getting barrel distortion at full zoom.... have no idea whether the benq suffers from this.

    Let us know how you get on......

    Sean.
     
  4. Mark Ward

    Mark Ward
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    Thanks for the replies.

    I really don't know much about DLP or LCD PJs, I didn't realise that DLP PJs suffered from "screen door" effect like the LCDs do. We've tried JohnS's HS10 in my room at 10ft and it's not bad at all. The screen door is visible, yes but still very watchable.

    I do have total light control in my room and normal seating would be around 1.5 x screen distance.

    I chose the Benq8700 based on reviews & stats with the final push being that they now ship with the HD2+ chip fitted. I was going to go for an HS20 as I can get staff discounts on Sony products, but the Benq seemed to be another step up again.

    I'm intending to buy locally, I have an understanding dealer who's used to my haggling and will usually sort out something close to online offers for an easy life (keeps me from nagging him). If he's able to get a demo one for me I'll take advantage of that first.

    I've got a Messiah & JohnS and NFordEnfield coming over to my place later this week. John's bringing his HS10 down again and Neil (Messiah) is bringing his S3 HD2+ DLP. We'll compare those against my Barco , which I realise is underpowered for my room.

    I would have loved to stay CRT, but a max budget of £3K (fitted), increasing pressure from the kids to play Console games at 10ft wide, and the fact that hanging a big CRT from my 18ft high ceiling seems very difficult have pused me in this direction.

    It should keep me going fo a couple of years whilst technology makes the next leap or 2.

    Mark.
     
  5. rOAdeh

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    2 things i've read from avsforum whilst keeping my eye on the benq is that:

    1) barrel distortion is not an issue though some people have been having faulty units... afaik these are replaced without question

    2) the benq is supposedly quite dim and therefore screensize is not recommended >8ft.. tho if you have a light controlled environment then i guess it might be ok to bigger.. depends how used to the dim barco you are ;)
     
  6. Mark Ward

    Mark Ward
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    I was thinking that there must be an element of light leakage or diissipation that would be more evident the further away the PJ was. Guess that's not right.

    I'm not looking for "Dim", I hadn't heard this about the BenQ, I have to say, more cause for concern there then.

    I've got Neil's Marantz S3 coming round today so I'll see a decent DLP @ 10ft for the first time:)

    Mark.
     
  7. Gary Lightfoot

    Gary Lightfoot
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    Hi Mark,

    That's an interesting comment you make. I wonder if conversely, because some projectors allow some light to be emited from the case via grills etc, you could possibly get some unwanted light reflected onto the screen from these orifices which would wash out the image a little. The closer the projector, the more likely this could be - depending on the projector of course.

    I wonder if light leakage does happen though as you suggest - it's not something I'd considered, and my first thought would be that this wouldn't be an issue due to the nature of the optics, but I wonder if there's a genuine consideration here.

    Anyone else care to comment?

    Gary.

    PS - Looking forward to your opinion of the S3. :)
     
  8. Mark Ward

    Mark Ward
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    Hi Gary

    I know about as much about the nature of optics as I do about CRT calibration (which is another reason to go DLP/LCD), but I just wondered whether a torch with a lens pointed on a wall from say 1M would give the same brightness as from 5M away and but zoomed to the same dimension patch on the wall?

    I thought the Marantz S3 was great, we all agreed it could have gone to 12ft and still looked good. It's only a 700 ANSI Lumens output, but with the 3800:1 contrast ratio the blacks were very nice and the picture lovely and vibrant. The Benq I'm seriously considering right now is 1000 ANSI lumens and 2500:1 contrast ratio it's revised HD2+ form. I don't think the Marantz is now in the right price/performance ratio though.

    I'm still stuck on what to do. I'm already reading with interest about the forthcoming HD3 Chip with it's 5000:1 ratio I'm wondering whether the HS20 would suit me OK until we see the next step forward. It seems that either PJ will be a stepping stone.

    The big question there though is "How much better than the HS10 is the HS20?" There's about £1200 between the Benq8700 and the HS20 and that's a carpet for my HT room (well nearly). Is a Benq8700 £1200 better than an HS20?

    Then again I could just stick with CRT for 1 more year which would be the cheapest option of all.

    Mark.
     
  9. Gary Lightfoot

    Gary Lightfoot
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    I'm sure there won't be any difference in brightness as the same ammount of light will be distributed over the same surface area of the screen in either zoom mode. 1000 lumens divided over the same area will still be 1000 lumens. When calculating foot lamberts (the reflected light) distance isn't part of the equation:

    lumens/square ft x gain = ft lmbts.

    It's a tough decision, but how much better (or worse) was the S3 than your CRT? The Benq will be inferior to the S3, but by how much? At least you have two projectors to go some way to guage the differences.

    There's always something new just around the corner, so it's difficult to know when to jump on. If you have something that you're pretty happy with, then it won't hurt to wait a while, especialy as prices are dropping and performance is improving. Whatever you buy will be old technology within a year though, and that will be reflected in its resale value, so if you think you'd be happy with it for 3 years, go for it.

    Gary.
     
  10. JohnWH

    JohnWH
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    Sorry to be picky, but why doesn't distance does effect brightness, light is after all electromagentic radiation, so intensity is inversly proportionally to the distance squared (1/r^2)? Obviously most peoples rooms aren't long enough for this to be the dominant factor!

    Edit: Hang on I'm just being thick, its 1/r^2 becuase of outwards radiation so the less divergent the beam...

    John
     

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