Constant height, throw distance, and other questions

Discussion in 'Displays' started by Joel Stein, Jan 4, 2006.

  1. Joel Stein

    Joel Stein Stunt Coordinator

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    Hey all, newbie here so please be gentle...

    16' x 13' family room. I really want a constant height set-up. I'm on a budget, so I'm thinking something like InFocus 4805 or SP5000 with a lens. My questions--

    To figure out the layout of the room and potential projector placement, I've gone to those projector calculator webpages. But they all assume 16:9 screen, not 2.35:1. So how should I use these calculators? Use height, even though my actual screen width will be greater than theirs, or use width, even though my actual screen height will be less than theirs? Follow what I'm getting at?

    I've searched forums about CH set-ups, and most people talk about easily switching between 16:9 and 2.35:1 aspect ratios. But everyone seems strangely mum on how these set-ups handle 4:3. Anyone? I have lots of old movies.

    What about other less-common aspect ratios such as 1.66:1 or 2.00:1? Do you simply use the projector's zoom to compensate? If I understand correctly, the InFocus projectors do not have remote zoom, so you'd have to do manual zoom then. (A serious pain in the ass if you use a ceiling mount. That's why I'm considering using a shelf for the projector...but then I could run into throw distance/seating difficulties.)

    What about running vhs through a set-up like this? (Not everything is on dvd yet.) You'd have to bypass the anamorphic lens, but then how would one expand a letterboxed videotape to fill the screen? Zooming? Of course I understand it would look like crap, but hopefully if the screen isn't too large, it would look merely like crap instead of absolute super-duper crap.

    Finally, am I correct that overscan is not an issue with front projectors?

    Thanks!
     
  2. John S

    John S Producer

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    The SP5000 definetly has an overscan feature you can turn it off and on.

    I am scared to death about how it will handle non anamorphic widescreen myself to tell you the truth and not even a CH setup.
     
  3. Joel Stein

    Joel Stein Stunt Coordinator

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    "Overscan feature"-- What is this, what's it do? Under what circumstances would you want it on and when would you want it off?
     
  4. John S

    John S Producer

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    I have one of these projectors comming, and in the manual it says that if your picture looks bad or has garbage/ect..ect.. at the edge of the images, turn overscan on. I am supposed to have the projector tomorrow, I've been reading up in hopes of a quicker and easier installation.


    Page 14 of the User Guide:
    http://www.infocus.com/service/sp500...000-ug_eng.pdf
     
  5. Mark Techer

    Mark Techer Agent

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    Some CIH chat, cool[​IMG]

    Joel,

    The 4805 is a great projector and will work well in a CIH set-up. You've asked about the playback of older material that is non anamorphic. There are two ways to do this -
    1. remove the lens. You've mentioned that you are going with a shelf install so that sound not be too hard.
    2. choose a lens with a pass through mode like Prismasonic.Here is a link to their website.

    You've also asked about choosing a lens and about zoom.

    When ever possible, avoid the use of lens zoom as the increased image can cause artifacts when passing through the adapter, including but not limiting to, clipping the image from the light beam being too big to pass through the lens. CA tends to get worse as well.

    How large is your screen? There are two basic types of lens
    1. HE or Horizontal Expansion
    2. VC or Vertical Compression

    A HE lens is great when you need or want to create a set up that allows to you remove the lens (as the vertical height does not change) or if you need a larger screen and your at your limit so far as throw goes.

    A VC lens allows you to create a CIH when the projected light beam is to large. They do not suffer CA at the edges as bad as HE lens and do not suffer pincushion like HE. There limits come when you want to remove the lens. The image tends to get a down tilt with the lens in place as well as expands vertically when the lens is removed. Therefore some readjustment is in order if you intend to remove the lens. A HE lens is simpler...

    Mark
     
  6. Joel Stein

    Joel Stein Stunt Coordinator

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    Thanks for the reply, Mark; I had figured this thread had seen all the replies it was going to see.

    Some very useful information. Looks like HE lens would be the way to go for my needs. But one question:

    What's "CA"? I'm sure I probably know, but I'm not figuring it out from the initials.
     
  7. Mark-P

    Mark-P Producer

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    I can't offer any comments about special lenses, but in my home theater set up, I use the constant-height method. I use my Benq pe7700 as a tabletop straight out of the box (no modifications). I find that I can accommodate both 1.78:1 and 2.35:1 without moving the projector by using the zoom. However, just zooming larger causes the picture to then be several inches too high on the screen. I compensate for that by using the vertical position adjustment in the projectors menu to lower the picture. But even at it's lowest position it still won't quite make it, so I use a small shim to slightly tilt the projector down.
    Sound like a pain? Sure, but it's the poor mans way and it works beautifully.
     
  8. John S

    John S Producer

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    CA is what happens in lower end optics. Amounts to some purple / blue fringing at the extreme edge of the picture.

    Ever heard the terms Achromatic -vs- Apochromatic?

    CA is present in Achromatic optics.
     
  9. Mark Techer

    Mark Techer Agent

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    I was doing this for while too but really did notice a huge difference once I got my lens. The beauty of using the lens is that you get to use all of your vertical pixels all of the time. The image is easier on the eye and therefore less fatiguing. Allot of people baulk at the price of the adapters (and I did too, so I built my own 4 prism lens) but the prices are coming down with both Panamorph and Prismasonic offering entry level HE (Horizontal Expansion) lenses...

    Mark
     
  10. Mark Techer

    Mark Techer Agent

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    And HERE is a picture...

    This image is from my new 4 prism lens...

    Mark
     
  11. ChrisKen

    ChrisKen Auditioning

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    FWIW, CA actually stands for Chromattic Abberation. It can be present in Apochromatic optics, but Apochromatic optics use very rare metals as coatings (i.e. expensive optics) to reduce it to null.

    Cheaper department store telescopes of the refractor variety usually display "CA" on bright objects like the moon and Jupiter, as a prime example.

    Yes, its a purple halo or fringing caused by the color spectrum being projected out of focus.
     
  12. Joel Stein

    Joel Stein Stunt Coordinator

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    Mark-
    Yeek! Is that difficult to do, especially if one has little knowledge of optics, little handy-man ability, and no handy-man equipment? I'm not sure I would have enough faith in my limited abilities to be worth saving money on a professionally built lens.
     
  13. Mark Techer

    Mark Techer Agent

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    I found a plastics engineer who made both sets of prisms for me - one 2 prism lens and one 4 prism lens.

    In the end, it is a substantial saving, as commercial lenses start here at around $1500, and go through to (ready?) $13 500 for the ISCO III with auto slide. So spending less than $100.00 on the development of a lens that can produce good results is well worth the effort.

    I am about to build a new lens, and this time I will do all the work myself, save for the cutting of the parts...

    Mark
     

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