Image Size & Viewing Distance - AVS Forum
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post #1 of 7 Old 08-19-2000, 04:04 AM - Thread Starter
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The subject of viewing distance emerged as a spin off from a thread in the single lens (LCD, DLP, DILA) projector forum. I began a new topic in the screen forum because I thought this kind of discussion might be more appropriate here than in the thread where the subject arose.

In the other thread, I happened to mention the dimensions of my screen (7' by 14') while discussing a related matter. This prompted Bob Wood to ask how far away from the screen I sit when viewing. As I started to reply, I realized that simply saying 12 to 14 feet without some explanation might seem pretty outrageous in view of SMPTE recommendations. So, Bob, let me try to explain my approach to viewing distance as it has evolved over the years.

First, 7' by 14' is the screen size when the masking curtains are fully open. However, I do not use all of that screen area with my current projector (6 year old Sharp XV80U LCD, w/ VGA res). It's dated technology cannot project a decent quality image THAT large. The screen width is 14' because the approximate distance between my right and left front speakers is 14', and the 7' screen height leaves a 1' space for my center channel speaker below the screen. Since, the room is fully dedicated to the theater, I figured the wall between the speakers wouldn't have any other function anyway, if it wasn't anchoring a screen. So, I ordered the Draper fixed frame with the M2500 material to cover the entire 7' X 14' area. I knew it was too big at the time (1995), but I hoped the future would bring more capable, higher res projectors along with HD video. At that time, I also installed a Makita curtain system so I could mask off whatever portions of the screen I did not want to utilize. This set-up permits any size image and aspect ratio within the parameters of the 7' by 14' fixed screen.

Second, somewhere along the way I read that SMPTE recommended viewing distance was approximately 2.5 times screen height. With that in mind, I began experimenting with various image heights by using the projector's 1.33x zoom function. I found that 2.5 times height seemed a tad small for my tastes---I guess I wanted a little more cinematic impact. Anyway, I finally settled on a picture height of about 64 inches, which puts the nearer seats in my theater too close according to the 2.5x standard. I have since heard differing numbers, so I may have gotten the SMPTE standard wrong in the first place. Regardless, I liked the feel of the image size I had chosen---for me it didn't seem too big. The resulting picture from my 1.33 aspect ratio projector measured 64" by 85".

Third, it wasn't long until I was wanting to maintain the 64" height when watching widescreen movies (1.85, 2.35, etc). To achieve this constant height, variable width approach, the projector's zoom was my only tool for several years. Then came DVD with its anamoprhic capabilities, followed eventually by the ISCO anamorphic lens (introduced to me through AVS forums). These two developments have made it possible for me to maintain image height while expanding the width to fill as much of my 14'screen as I dare. The limited video quality produced by the gear I now have causes me to prefer a width of no more than about 11.5 feet on 2.35 ratio material (55" by 138" with the ISCO). Not quite where I want to be, but anything larger shows too many of the weaknesses in my aging projector and in NTSC video itself.

Fourth, my experimentations along the way suggested to me that picture height, much more than width, was the factor which determined whether a particular image seemed too large. In other words, expanding the width of a fixed height image could add much cinematic impact without overwhelming the viewer. However, when the height is expanded too much (subject to individual tastes), the picture starts to feel overwhelming, i. e., uncomfortably large, regardless of width.
For me, a 64" height in any aspect ratio remains comfortable at viewing distances of 12 to 14 feet. All of this, of course, is just personal preference---you remember the crazy kid who always liked to sit on the first row of the local Bijou...yeah, it was me. http://www.avsforum.com/ubb/wink.gif

Fifth, none of this big screen size/viewing distance talk is very helpful if the video quality is not up to the challenge of cinematically large images. I am encouraged that the new projectors, processors, and high definition video sources I always hoped for are in development or starting to become reality. I wish I knew how much longer it will take to get HD DVD for instance; but, as usual, my crystal ball is fogged over. Before TOO long, though, I believe we will have affordable video technology capable of a stunning widescreen display on larger screens than we ever thought possible. It can't happen soon enough for me!

Well, Bob, I have given an overly long answer to a very short question, I know. Probably still left out something, despite my long windedness. In any event, I hope I have been clear enough for you to see where I came from and where I want to go with respect to image size and viewing distance. Very little of this may apply to anyone else, but the quest has sure been fun for me.

Have fun! http://www.avsforum.com/ubb/smile.gif



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post #2 of 7 Old 08-19-2000, 10:04 PM
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Tom,

I'm surprised you can get away with this large a fixed screen for several reasons:

1) It seems like masking top and bottom has been left out. Or does your Makita curtain system handle that as well as the sides ?

2) Even 85"x64" is a pretty far stretch for a 640x480 projector. That's only 300,000 pixels.

Even so, if you are playing 16:9 material at 65x115 and sitting at 14', then you are at about the same ratio distance/width I plan to sit. The difference is that I will be using a D-ILA projector at 1360X1024 -- about five times as many pixels ! That you are happy with your ratio gives me hope. I've found that my preferred seating in a commecial theater is just under 1.5 times the screen width. If that holds true at home, then I'll be right on target at 12' from an 8' width screen.

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post #3 of 7 Old 08-20-2000, 04:45 AM - Thread Starter
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Dreamer,

I'll try to answer your questions/comments in turn.


[quote]Originally posted by dreamer:
Tom,

I'm surprised you can get away with this large a fixed screen for several reasons:

1) It seems like masking top and bottom has been left out. Or does your Makita curtain system handle that as well as the sides ?

Sorry, I did not mention that the screen goes all the way to
the ceiling, which we have decorated with light absorbing
material similar to that of the side curtains. The bottom is
masked with another light absorbent curtain, vertically
adjustable from 1' high to about 4'. Movable curtains on three
sides (right, left, bottom) provide enough flexibility that
the fixed screen doesn't really seem fixed---it is relatively
simple to vary the aspect ratio and size of the usable screen
area. I guess pictures of all this would be helpful, but I don't
know much about how to post photos to the forum.


2) Even 85"x64" is a pretty far stretch for a 640x480 projector. That's only 300,000 pixels.

I agree. That's why I'm looking very hard for a new, higher
resolution projector right now. Lately, I spend most of my time
here at the AVS website on the LCD, DLP, DILA projector forum.


Even so, if you are playing 16:9 material at 65x115 and sitting at 14', then you are at about the same ratio distance/width I plan to sit. The difference is that I will be using a D-ILA projector at 1360X1024 -- about five times as many pixels ! That you are happy with your ratio gives me hope. I've found that my preferred seating in a commecial theater is just under 1.5 times the screen width. If that holds true at home, then I'll be right on target at 12' from an 8' width screen.


I would just say have fun with it. If you like it large, make it
large for cinematic impact...if you like it smaller to hide more of
the weaknesses of NTSC video, do that. One nice thing about home
theater is that it's YOUR theater. If 1.5 times screen width suits
you, go for it. I experimented until I found a size with which I was
comfortable. Even with a low res projector, people who watch movies
with us seem to really enjoy the experience of a big screen---a
projector upgrade will make it that much better. BTW, I hope to get
a demo soon of a DILA unit. That kind of resolution sounds great,
especially for somebody like me who prefers a large image.


Happy home theater-ing!








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post #4 of 7 Old 08-21-2000, 12:49 PM
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Tom,

Had you experimented with the Cygnus de-pixelation lens to get a smoother image ? Or would that interfere with the ISCO lens ? And how does a 640x480 projector deal with a 720x480 DVD as source ?

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post #5 of 7 Old 08-22-2000, 03:07 AM - Thread Starter
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Almost a year ago, I tried the Cygnus Imaging depixelation lens, but didn't get the results I was looking for. Right off the bat, it did not seem to fit as it should on my projector's lens. After struggling with it, I felt it was not the correct model for my particular projector, but Cygnus told me otherwise. Anyway, it managed to attach adequately enough for its effect to be observed. There was a softening of the image which obscured pixels, but, for my money, a very similar effect could be produced by very slight and very careful defocusing (a method I had used for years). Moreover, there was also a noticeable loss of light and apparent contrast. I asked Cygnus about this, and they said that a minimal light loss had indeed been measured by their engineers. I doubt that this will be an issue with the newer and much brighter projectors currently available; but my older, dimmer machine really couldn't afford any light loss or contrast degradation. I ended up returning the lens to Cygnus, although other forum members have used this product quite successfully. Maybe, if I could be certain of getting the right model for my projector, a second try would go better...who knows.

I don't have any 1.5:1 ratio discs (480 X 720)---perhaps that is a format used outside my DVD region? In any case, I assume your question basically concerns how anamorphic 1.77 ratio DVDs are handled by my 1.33 fixed panel display device. I just set my DVD player to "16:9", outputing the 1.77:1 format to my 1.33:1 projector. The anamorphic video is then displayed through my 1.33 device in a "tall and skinny" horizontally squeezed manner. The ISCO anamorphic lens adapter then provides a horizontal expansion to unsqueeze the video for viewing. I use the projector's zoom to maintain or re-establish image height for the screen size I have chosen. The masking curtains can then be positioned at the proper positions to the sides and bottom, and we are off to the movies!

Let me add that using more of the projector's 1.33 panel with these anamorphic discs helps pixel density. Compared to "letterbox", I am able to get something like 33% more vertical resolution from the 1.33 panels using the DVD player's 16:9 output combined with the anamorphic lens adapter. Also, the ISCO causes a shorter throw ratio which, in turn, allows the image to be zoomed smaller when the lens is applied for horizontal expansion. Thus, the pixels have greater density because of the anamorphic format and reduced size because they are zoomed smaller for display through the ISCO. The overall result is an image with less visible pixels. What I still need, though, is a higher res projector. http://www.avsforum.com/ubb/smile.gif


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[This message has been edited by Tom Hilton (edited 08-23-2000).]

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post #6 of 7 Old 08-22-2000, 10:41 PM
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Tom,

Yes, I'm familiar with the efects of the ISCO. I was ready to buy one when the Cygnus Panamorph was announced. Now I have it on pre-order and have high hopes for it.

You know, I've seen that number 720x480 so many times and yet never noticed it was a 1.5 ratio ! But it is correct. Right now I have The Fifth Element playing in my TPC and PowerDVD reports the source picture resolution as 720x480. It does seem odd, though.

And both 16:9 and 4:3 material has the same 720x480 source picture resolution.

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post #7 of 7 Old 08-24-2000, 11:53 AM - Thread Starter
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Kirk,

Like you, I have seen "480 by 720" before without thinking about the aspect ratio it represents. However, maybe I am starting to understand what your PowerDVD program is reporting about the 480 X 720 res. The 1.5 ratio seems to be something of a compromise between 1.33 and 1.78. Might it be that the DVD itself has a standardized 1.5 ratio with a max pixel count of 480 X 720, regardless of the aspect of the video it contains? If that is true, the implication seems to be that on 1.33 video material, the full vertical res of 480 is used, while only 640 of the available 720 in horizontal res is used (480 X 640). On the other hand, with 1.78 material, the full horizontal res of 720 can be utilized, but only about 405 of the vertical res (405 X 720). I am no expert on this and could be misinterpreting the whole thing---just trying to think it through. Am I completely mistaken, or have I stumbled inexplicably onto the truth? http://www.avsforum.com/ubb/smile.gif

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