2.35:1 Constant Height Set-ups

Discussion in 'Displays' started by Mark Techer, Oct 7, 2005.

  1. Mark Techer

    Mark Techer Agent

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    Sorry if there is another thread on this topic, but I have just recently installed an anamorphic lens to allow my 16:9 to display 21:9 at the same height.

    The experience is approaching cinematic quality and I would not go back to standard 16:9.

    How many other have done this?

    Mark
     
  2. JeremyErwin

    JeremyErwin Producer

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  3. ChrisWiggles

    ChrisWiggles Producer

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    There are quite a few people who do this, and there is good reason both cinematically and in terms of resolution if you watch a lot of movies wider than 16:9 on a digital display with a 16:9 panel.
     
  4. Mark Techer

    Mark Techer Agent

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    So is there a constant height discussion on this site or is everyone referred over to AVS?

    Mark
     
  5. Jay Mitchosky

    Jay Mitchosky Producer

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    Actually, there is a new evolution afoot regarding constant height vs. constant width. Runco/Vidikron now have a new option on select projectors that is, frankly, amazing. It's called Autoscope with Cinemawide and includes digital and optical components. First, the 2.35 image is digitally stretched vertically to fit the entire 16:9 display panel. Result, geometry goes haywire but now all of the panel's pixels are used to write image information vs. black bars. Next, when a 2.35 AR is detected an internal anamorphic lense automatically locks into place to restore correct geometry projected onto a 2.35 screen. You then employ a masking system on the sides that draw in for narrower ARs.

    The fully automated approach runs for US$13K just for the option. But manual setups as described above will accomplish similar results (although with slightly less resolution as you would need the digital algorithm to complete fill the 16:9 panel).

    If you think about it, this is really long overdue. 16:9 has always been a compromise to meld 4:3 and film ARs. Great for a general home environment but still falls short for true home theater. I think more manufacturers will start to develop similar solutions that will accommodate dedicated theaters.

    The flipside is that constant height somewhat compromises the idea of achieving a specific horizontal viewing angle when planning seating (or screen size). With constant width you accommodate typically a 30 or 35 degree field of vision and you're done with it. With constant height presumably you base screen size (or seating distance) on that field of vision for the 2.35 image (widest that will be presented) but sacrifice 1.85 slightly with a narrow angle and less scale. A modest trade-off, though, considering that most films seen today are in the 2.35 AR and the difference in viewing angle would be slight at best. If you plan for achieving the SMPTE minimum 30 degrees on the 1.85 image that should get you to around 33-35 degrees on the 2.35 (if I had time I would do the math).

    I believe this will define the dedicated home theater in the not-too-distant future.
     
  6. Mark Techer

    Mark Techer Agent

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    Something that I feel needs clarifying - constant height varies width only and is capable of displaying all aspect ratios from 1.33:1 to 2.35:1 at the same height. Scaling and an anamorphic lens will be needed in addition to a 16:9 projector.

    Technically speaking, if you own a 16:9 projector and never display anything wider than 1.78:1, you have a constant height setup. One you exceed the native aspect ratio, you then enter the constant width set up.

    Constant width is pretty much what anyone running a projector has now, that is the width does not change, but the height of the image will be reduced to fit in the width of any program that is wider than than the native aspect ratio of the display, that is black bars are seen top and bottom.

    Constant area is a compromise to both, but gives roughly the same picture area for both 2.35:1 and 1.78:1 through the use of both side and top/bottom masking and in some casing a vertical squeeze lense and external scaling.

    My Constant Height Set-Up...

    I have two rows of seats in front of my constant height setup.

    I chose the THX "preferred" viewing angle of 36 degrees from the back row to the screen for 2.35:1 and I chose the same angle from the front row to the screen for 1.78:1, therefore sitting in this row for "scope" films is a real eye full, but I don't mind sitting this close.

    The screen width was chosen by using the minimum THX standard of 26 degrees from the back of the room.

    So what you end up with is three subtended triangles for max screen width, minimum and preferred seating distances from the screen.

    The source (DVD) is set to 16:9 and therefore provides the horizontal squeeze needed to work. The projector is not set to 16:9 stretch, but rather is set to both 12:9 and 16:9 zoom modes. What I end up with (without the lens in place) is two aspect ratios of tall and thin video. The video must be seen this way so that the lens can optically stretch the image. Normally we would electrically stretch the image, but now we optically stretch it.

    The 12:9 mode + lens gives an aspect ratio of approx 1.78:1 and is used for all films that are either 1.78:1 or 1.85:1. There is only 4% variance between the two.

    The 16:9 zoom mode (this is actually a 4 x 3 mode but zoomed to fill the 16:9 panel) chops off the top and bottom of the image. This is used to our advantage as we effectively chop off the black masking bars of 2.35:1. Again the image is tall and thin, and we optically stretch the image to restore the geometry. So 16:9 zoom + lens = 21:9 (2.33:1).

    The only limitation is sometimes subtitles are also chopped if they sit on the masking bars at the bottom of the screen.

    Mark
     
  7. Jay Mitchosky

    Jay Mitchosky Producer

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    That's a clever compromise to have the chosen angle for both ARs.
     
  8. Mark Techer

    Mark Techer Agent

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    Thanks Jay,

    Initially, the front row was going to be some where to put "the kids", but once watching both ratios from this distance, it seems that because the height is comfortable (calculated on 36 degrees for 1.78:1 width), that extra width is not an issue either. My understanding is that our eyes do not fatigue as quickly horizontally as they do vertically. It only becomes a problem when the screen is too tall, and or if the pixels are visible.

    The lens has softened the pixel structure (possibly through the horizontal stretching), but the scan lines are sometimes visible (during fast motion), but because they run horizontally, don't seem to distracting at the closer distance either...

    Mark
     
  9. Jay Mitchosky

    Jay Mitchosky Producer

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    What are you running for vertical angle? There are a couple schools of thought here. The basic rule of thumb is to align your eyes (in the main seating position) at 1/3 of the way up from the bottom of the screen. A more detailed alternative recommends a specific angle measured between the horizontal plane of your eyes against the top the screen - I believe that angle is around 14 or 15 degrees. I've considered both for the planned placement of my screen and I find the wider vertical angle is a little overbearing vs. aligning 1/3 of the way up.

    What you say about fatigue would certainly make sense as our eyes are designed to work on a wider horizontal plane than vertical.
     
  10. Mark Techer

    Mark Techer Agent

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    Jay,

    I haven't finished my risers yet, but the back row should place the eye line just above vertical centre of the screen, I will have to be careful here as heads will be close to the projector and lens, especially when standing on the riser, just before sitting. The front row will be a bit below that. I haven't really calculated these angles but as I go to a real cinema quite often (with stadium seating and and awesome sound system), I just want to try and re-create that experience in my home...

    Jack,

    Your screen is flat. Does the Panamorph not suffer barrel distortion or pincusion? My lens is home made (scroll down the same link)and I had to build a curved screen to compensate for both...

    Mark
     
  11. Mark Techer

    Mark Techer Agent

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    Jack,

    You've stated that your screen frames are from an older 16:9, so, aluminum(?). If attached to a wall at centre, could you force wedges at each end to bow the screen? I should think that you might have to re tension the middle as well though...

    Mark
     
  12. Jay Mitchosky

    Jay Mitchosky Producer

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    Presumably the screen should form an arc with each point equidistant from the center of the lens?
     
  13. Mark Techer

    Mark Techer Agent

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    Jay,

    In regards to your "off Topic", lens shift, are you referring to products like the Panny AE700U? I want to try one of these with my lens, but so far, not too many people understand the concept or the physic behind optically stretching an image.

    The other related issues with home theatre projector stems from the fact that most of what we have today started off as data grade units used for large screen presentation, not video. Over the year each manufacture produced dedicated video units, but I still feel that things like short throw and limited zoom go back to the data days...

    My first projector a Sanyo 4 x 3 LCD, 1024 x 768 and I had plenty of zoom range at my chosen mounting location. My next purchase was the Sony HS1, same specs, but nowhere near the zoom range and in the end the zoom was just under max to reach the same size screen from the same mount.

    my latest, the HS-3 is just stupid as it works at just half the throw distance needed for the HS-1. The problems with using these projectors and an anamorphic lens is that you don't really want zoom, as that just adds all sorts of artifacts to the projected image. But to get a decent sized screen you also need to or want to put the projector back as far as possible, but with the inability to minimize zoom, there is not way this can happen, and in my case, the projection rig is right above the front seating location. ..

    In regards to the 2nd quote. My screen is plastic (they type used by laser cut letter signs). It came with a protective layer and is fairly rigid vertically.

    My LCR baffle is three pieces of MDF (with cutouts for the speakers) and is hinged. The screen attaches only to the left and right sides. As I toe in L and R speakers for better imaging, the screen bows also. I am therefore able to align the curve to match the barrel distortion. Its not perfect, but works well enough...

    The reason I suggested wedging the screen, is that there are many manufactured screens using the aluminum extrusion as frames. With a miter saw it would be easy to cut down the height and retain the width to change the aspect ratio. But they are all flat, and I figured that once bent, they would pretty much stay that way. But careful, symmetrical bending would be in order, hence pre cut wedges...

    Mark
     
  14. Mark Techer

    Mark Techer Agent

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    Hi Jack,

    My screen is flexible due to the way it is mounted. It attached to the ends only of a 3 panel, hinged array. With the centre remaining in position, all I do is simply bring forward each end until the curve of the screen matches the curve of the image. It might seem a bit hit and miss, but it works [​IMG]

    Sorry I don't have a mathematical answer for you, but the bow of my screen is only about 2 - 3 inches for a screen width of 96", so it should be less for your 70".

    I would try 4 small timbre wedges like door stops first. Good luck and I will be interested to read how that goes...

    Mark
     
  15. Mark Techer

    Mark Techer Agent

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    "Presumably the screen should form an arc with each point equidistant from the center of the lens?"

    Well I would have thought so too, but as it turns out, it is closer to R x 2 (where R is the radius of the circle).

    I'm interested to read what other have to say...

    Mark
     
  16. Mark Techer

    Mark Techer Agent

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    Please don't let this thread go the way of the dodo...

    I think 2.35:1 is something that will catch very quickly once there are affordable lenses...

    Mark
     

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