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Seleco projector Throw / distances ??

Discussion in 'Projectors, Screens & Video Processors' started by cosmic023, Sep 30, 2003.

  1. cosmic023

    cosmic023
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    Hi All,

    Well i'm in discussion about a purchase of a Seleco 350+ CRT projector.

    The thing i need to know is what's the throw distance between projector and a 70" wide screen ?? (Not yet built)

    After looking at the brochure / info data i have, there are details for a 60" screen, and the next size up is 80" which is over the x1.5 distance between the seating and the screen.

    The thing that matters me is it's setup for a 6' 4:3 wide screen, and i'd prefer to take it out to 7' 4:3 screen. How would i work out what i needed for the lens spacers ?? Or is there some kind of forumula ?? I know it would have to be setup from scratch again.

    After reading many posts in this forum, i'd prefer to have a 4:3 ratio screen instead of a 16:9 screen. But then i do watch a 75:25 split between 16:9 & 4:3 material.

    What are your thoughts people ??

    Cheers

    Cosmic023
     
  2. Chris Frost

    Chris Frost
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    The brochure/manual is talking about 60" and 80" screen diagonals (corner to adjacent corner). It isn't clear from your post if you 're talking width or diagonal.

    Do you want a 7ft diagonal (84") 4:3 picture - this would be 67.2" wide x 50.4" high
    or
    a 70" wide x 52.5" high 4:3 picture (which is 87.5" diagonal)

    Here's a good tip. Just work on screen Width (side to side) and then multiply by 1.5 to give the lens to screen distance.

    A 70" wide screen needs a throw distance of 105" from the screen to the projector lens.

    The lens spacers are listed in the user manual for a variety of 4:3 screen sizes in (diagonal) inches and at three different tilt angles - 12 degrees (which is the projector mounted level) or 15 & 18 degrees where the projector is mounted higher than the top edge of a 4:3 screen.

    Regards
     
  3. cosmic023

    cosmic023
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    Hi Chris,

    Sorry about the confusion, i'm going to be setting up a 70" wide x 52.5" screen. (87.5" diagonal)

    Thanks about the info about the spacers. It's just this is my first CRT projector, and i know it's gonna be a bit more of a chalenge than setting up a LCD projector. But i'm after, a film like quality picture, and with good contrast levels that you get from a CRT projector, so i'm trying to take on as much knowledge as i can, before installing it.

    I've noticed in the manual about lens angles, but how do you work this out, when you install the projector ?? Do you use some kind of laser pointer device ?? Or is there an easier way ??

    Cheers

    Cosmic023
     
  4. Chris Frost

    Chris Frost
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    There’s an easier way. Firstly, you’ll know if the projector is hanging level or not just by looking at it.

    If it’s level then look up the 12 degree shims for your screen size and put them in on the green lens only. Use just the green lens and then display the H characters from the built in test patterns; if you can focus the green lens so the image looks sharp from top, through centre to bottom and in all four corners then use the 12 degree shims for Red & Blue also.

    If you find that the image is sharp from top to centre but softer at the bottom then try the 15 degree shims.

    Regards
     
  5. cosmic023

    cosmic023
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    Hi Chris,

    Thanks for the info, i'll keep that in mind when setting it up.......

    As for the unit it's a 350 and not the plus version, but it has the AKB line mod ?? What is that ?? Is it some sort of auto tuning device ??

    I've decided on a 87.5" diagonal screen now, but the thing is the projector throw vs seating position and screen distance.

    By my calculations i've got a 96" distance from seating position to the screen, which i know is 9" short (70" x 1.5=105") but i can live with that.

    But where the projector is gonna be mounted, it's gonna be a 120" throw between the lenses and the screen. Do i need to rethink my mounting position ?? Because i've gotta strengthen the ceiling beams first, before i can mount it. Not really enough room to floor mount it. (Attic Room 12' x 13' approx, low 7' ceiling)

    I'll get there soon enough.............

    Cheers

    Cosmic023

    PS: If you wish i can PM you a more detailed room layout ??
     
  6. Chris Frost

    Chris Frost
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    The AKB line is used by the projector to monitor tube emissions. This is how the projector checks and maintains it's own colour balance. The AKB Line is projected a few inches above the top of a 4:3 screen. Prior to the mod this line would shift down and park on the screen area when you switched the projector to 16:9 mode. It would then go back up when you switched back to 4:3

    The mod keeps this line parked in the 4:3 position all the time.

    Right, now to screen sizes throw distances and seating position...

    first off, yes I think you need to rethink the projector mounting position.

    At 120" the projector is 15" further back than it needs to be. This means the picture will be bigger than your screen size. To compensate you'll either try to blank off lots of the overspill which will mean losing an extra 12% of the picture, or you'll reduce the size setting which means using a smaller portion of the tube to generate the picture. The knock on effect is that resolution will suffer (particularly with 16:9) and you'll lose brightness and increase the rate of tube wear.

    For a 70" wide image the lens to screen distance is about 105". The bracket will be a little further back of course, but try to stick to 105" for the projection distance.

    next, seating position. The accepted method is to put seating about 1.8 or 2 x screen width back, so the layout is Screen - Projector - Audience. For your 70" wide screen that means 126" - 140".

    I have seen installs where people sit level with the projector and are still happy but you will see more line structure especially on 4:3 and non anamorphic letterbox transfers. I haven't come across anybody sitting in front of the projector as you seem to be planning.

    You might have very good reasons that I don't know about for planning the layout in the way you suggested, but my advice would be to look again at the layout and see if these ideas could work for you. From personal experience I know they'll help you get the best results from the equipment.

    Good luck.
     
  7. cosmic023

    cosmic023
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    Hi Chris,

    Thanks for the info........

    After posting last night, i did realise after seeing many pics of CRT instalations on various websites, that i'd have to rethink about my setup.

    So now i've gotta rethink about the whole structure / room layout, i'll have to plan out a new design using the exsisting data i have.

    I did notice on most of the photo's about the screen / projector / seating positions.......that's when the alarm bells started to ring and thought about my room layout plan.

    Oh well so off to the drawing board again.............

    I'll suss this CRT thing out eventually.

    Thanks again.

    Cheers

    Cosmic023
     
  8. cosmic023

    cosmic023
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    Hi Chris,

    Spent this afternoon working out my figures, and i think i've come up with a winning solution ?? (I think ??)

    I've reduced the screen to 62" x 46.5" (Was 70" x 52.5") Not sure how to work out the diagonal ??

    Right the projector throw is 93" to the screen, and that leaves about 32" from the front of the projector to the wall. So that'll leave 4 1/4 " behind the projetor for cables and air space.

    As for the screen / projector / seating formula, i've worked it so the front of the projector is pretty much overhead of the seating position. You did state in your last post "you will see more line structure especially on 4:3 and non anamorphic letterbox transfers." Is this even after using an HTPC for scaling duties ??

    I can't get it better than that, unless i reduce the screen even more, which is something i don't want to.......

    What type of lenses are in the Seleco 350 ?? Are they short or long throw ??

    So i think this setup should be ok now ??, what are your thoughts ??

    Cheers 4 now

    Cosmic023
     
  9. Chris Frost

    Chris Frost
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    Cosmic, what is it your understanding of how a HTPC system will work with the 350?

    They're about in the middle - neither long nor particularly short but about average for CRT projectors. The throw ratio for the lenses is 1.5x ; hence Screen Width x 1.5 = Projection Distance :)
     
  10. cosmic023

    cosmic023
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    Hi Chris,

    I'll be using a HTPC to use as a scaler, running a tv card and dscaler.

    So i'd be doing the video like this:

    External DVD player / TV Card & HTPC / CRT Projector

    As for the resolution / line thing, i'm just asking if by using the HTPC, which i can use for a dscaler and connect via a VGA to x5 BNC ?? And would i still see the scanlines from where the projector is loacated ??

    What did you think about my projector layout ?? And how do you work out the diagonal of a screen ??

    Cheers

    Cosmic023
     
  11. Chris Frost

    Chris Frost
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    I thought that might be your answer. I'm sorry to break the news to you but the 350 isn't designed to accept a scaled signal. The RGB sockets only work with a standard video signal, not a PC.

    If you want to use a HTPC system you'll need to up your budget and invest more money into a projector that accepts at least 32kHz (line doubled/VGA) or something even higher. We're talking about Seleco 4xx/500/7xx/800/900 series, Barco 7xx/8xx/12xx, Sony VPH12xx/D50/G70.
     
  12. cosmic023

    cosmic023
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    Hi Chris,

    That's what i thought about using a HTPC, but i'd thought i would ask anyway.

    So if the HTPC is out, could i link it RGB via my dvd player ?? I know it does s-video, but RGB would be better ??

    Would that be via a scart socket or x5 BNC's for R,G,B and H/V sync ??

    Seems like i'd need to invest in a stand alone scaler then ?? Is their anything available that is reasonably cheap ?? Other wise i'll have to turn to fleabay & the classifieds ??

    I'm still wanting this projector as it'll be my first CRT projector, and funds won't allow to move to a Barco 801s yet. So maybe that'll be the next upgrade, unless something better turns up in a years or two ??

    Cheers

    Cosmic023
     
  13. Chris Frost

    Chris Frost
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    A 350 has an RGB enabled SCART socket or you could use the BNC connectors. The signal from DVD/Sky would use only 4 of the BNCs because the sync signal comes from the composite video output.

    RGB is better than S-video.

    NO!!:nono: This type of projector is like your average telly, it won't work with ANY sort of scaler (either HTPC or stand alone). Don't buy a scaler it won't work and you'll have wasted your money.
     
  14. cosmic023

    cosmic023
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    Hi Chris,

    Thanks for the advice, ok so this unit is limited to 15khz bandwidth, and isn't suitable for Scaler or HTPC use.

    Would i see scanlines in the picture if i can't use a scaler or HTPC ??

    So that's solved then, and i'll be connecting it via RGB then.

    Many thanks for your help, we'll leave it there until i purchase the unit and get it setup.

    Cheers

    Cosmic023
     
  15. cosmic023

    cosmic023
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    Hi Chris,

    Well it looks like i'm buying the 350 next week, so it should be interesting as things progress..........

    It's only done 1264 hours with no signs of burn on the tubes, and one owner for £500

    The pictures (Unit & Projected Film Pic's look amazing) from an Owl 6 ft wide 4:3 screen.

    As I already posted in another thread, i'm getting a Keene synblaster cable (Scart to x5 BNC's 10m) for connection from my DVD player and projector via RGB.

    What is the better format screen ?? I was thinking about building a DIY 62" 4:3 screen, but i was wandering seeing as i'll be watching over 75% 16:3 and the rest 4:3 material, would it be easier if i built a 16:9 screen instead ?? What is the best ratio screen for this projector ??

    Cheers

    Cosmic023
     
  16. Chris Frost

    Chris Frost
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    350s were designed to work mainly with 4:3 screens. For 16:9 anamorphic discs the picture width stays the same as 4:3 but the picture height gets squashed down. This means the best choice of screen for a 350 is a 4:3.

    Some people have used a work-around so they could have a 16:9 screen. All your ananmorphic and letterbox films will play fine, as will anything from Sky that is in 16:9 mode. Where you run up against a problem is with full frame 4:3 pictures. You either have to play them in 16:9 and accept everyone looking short and fat or just avoid 4:3 stuff.

    The best work-around is a 4:3 screen with adjustable black masking top and bottom. Arthur.S used this method very succesfully at his home cinema called the Baldyplex with a Seleco 320. The top masking was a black roller blind, the bottom was a home brewed solution. The result was something like black eyelids that closed over the screen. Arthur could mask right down to 2.35:1 or open right up for 4:3. It made a big difference to the impact of the picture.

    Regards
     
  17. cosmic023

    cosmic023
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    Hi Chris,

    Cheers for the info..........

    I was thinking about a adjustable masking screen, still not sure at the moment, still in the thinking mode at the minute.

    Also sent you a PM

    Cheers

    Cosmic023
     

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