Does a 2.35 anamorphic setup change SDE? - AVS Forum
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post #1 of 7 Old 02-09-2007, 06:00 PM - Thread Starter
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As I continue to obsessively ponder whether to go with a brighter 720p projector, or the current crop of dimmer 1080p projector, I have a few questions related to SDE (screen door effect) with 720p projectors and anamorphic 2.35 setups.

Q1 - When doing the proper vertical stretch with the projector or scaler, and then the horizontal stretch with an anamorphic lens, does SDE stay the same, get worse, or get better than it was with the 16:9 image?

Q2 - Does the usual recommendation of a 1.5 seating distance to screen ratio to avoid SDE with 720p work with a 2.35 screen width as well, or is it a different number?

Thanks,

Mike
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post #2 of 7 Old 02-09-2007, 09:19 PM
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Quote:
Originally Posted by mlbrand View Post

As I continue to obsessively ponder whether to go with a brighter 720p projector, or the current crop of dimmer 1080p projector, I have a few questions related to SDE (screen door effect) with 720p projectors and anamorphic 2.35 setups.

Q1 - When doing the proper vertical stretch with the projector or scaler, and then the horizontal stretch with an anamorphic lens, does SDE stay the same, get worse, or get better than it was with the 16:9 image?

That will be projector dependent. The anamorphic lens stretches the image by 33%, so your pixels are now 33% wider than before. The vertical height does not change.
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Q2 - Does the usual recommendation of a 1.5 seating distance to screen ratio to avoid SDE with 720p work with a 2.35 screen width as well, or is it a different number?

Thanks,

Mike

This will cause arguments for sure, but the said 1.54 times the image width was never meant for 16:9, but a "scope" 2.39:1 image. It was simply adopted by HT because LB Scope films look good at that distance. The reason they look good at 1.54x is because, if you then check the image height, you find that equates to about 3.68 time the image (not the screen) height...

It is said that with a HR projector like 1080, that you can sit as close as 2x the screen height...

Mark

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I love my Constant Image Height system!
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post #3 of 7 Old 02-09-2007, 09:47 PM
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Widescreen review has a write up on scope home theaters in Feb's issue. I believe they recommended 2.5x screen height for 1080 and 3x screen height for 720 projectors. I'll double check.

-Brian
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post #4 of 7 Old 02-10-2007, 07:14 AM - Thread Starter
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Quote:
Originally Posted by sleeks View Post

Widescreen review has a write up on scope home theaters in Feb's issue. I believe they recommended 2.5x screen height for 1080 and 3x screen height for 720 projectors. I'll double check.

sleeks,

I found that article in Wide Screen Review (WSR) and you are correct. The writer John Bishop notes that people are more sensitive to vertical pixels, so the screen height ratio should be used, not the screen width. He says that the 1.5 seating distance to screen width guideline was developed for 16:9 aspect ratio with 720p. He also says that the 2.5x screen height for 1080 is a conservative number and you might be fine even closer, but that 3.0 x screen height is what he advises for 720p. All the info I was looking for in one location!

That is a great article to read on home theater "scope" systems. I just recently subscribed to WSR but hadn't fully read that article yet. The writer did a lot of work with measuring lumens/foot lamberts in that article, and basically says that you can't get too bright, and that a bright "Scope" setup is breath taking. His article makes me think again that I should consider buying a high gain screen, but I guess that's another story.

Thanks for the find,

Mike
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post #5 of 7 Old 02-10-2007, 08:53 AM
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Quote:
Originally Posted by mlbrand View Post

He also says that the 2.5x screen height for 1080 is a conservative number and you might be fine even closer, but that 3.0 x screen height is what he advises for 720p. All the info I was looking for in one location!

These rules are not so hard and fast (though hard, fast, Rulez). As Mark stated this can be projector dependent. Any 720p that doesn't have an issue with SDE at a given screen width is unlikely to reveal image structure with a lens.

As an example the Smoothescreened Panasonics work just fine at larger viewing arcs.

ted
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post #6 of 7 Old 02-10-2007, 07:25 PM
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I am builidng a home theatre that will be 27' x 18'. I am planning on a CIH setup with a scaler and anamorphic lens on a motorized mount with a 60" high screen. That would give me a 141" width for 2.35 content. I will have three rows of 4 seats. I am anticipating that the front row will be 13.5' from the screen, the middle row 19.5' and the back row 25.5'. I will probably go with the new brighter Optoma HD81 projector and a Stewart screen.

I am just wondering whether the front row will be too close. The 1.54 times screen width has me concerned. I figure we will use the middle and back row most of the time and only use the front row once in a while probably for sporting events which is all 16:9.

Any opinions or suggestions are very much appreciated.

regards,

Don
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post #7 of 7 Old 02-10-2007, 08:19 PM
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Quote:
Originally Posted by Dontan View Post

I am just wondering whether the front row will be too close. The 1.54 times screen width has me concerned. I figure we will use the middle and back row most of the time and only use the front row once in a while probably for sporting events which is all 16:9.

Any opinions or suggestions are very much appreciated.

regards,

Don

I argue in favour of large viewing arcs so I am clearly biased. There is research that suggests that if you are going to sit farher than 1.5 then you are not deriving the benefits that will be offered with 1080P source and display.

This Document outlines it better than I.

We really should be viewing screen/viewing relationships by referencing screen height. SMPTE does. It can also be argued that the requirements for a THX theatre indicate that a ratio of 1.5 is the *minimum* viewing arc that is considered acceptable, so we really should be sitting closer if we are to be taking advantage of what the Human Visual System is capable of, and 1080 is finally going to deliver that to us.

As a comment on what we can be looking forward to from 1080 source note this comment from the Hi Def Insiders' Thread.

2 to 3 screen heights translates to 1.12 to 1.68 in terms of screen widths for a 16:9 ratio screen.

Ultimately though, it is your setup (and I'm envious) and it is what makes *you* feel comfortable not what a bozo who sticks his nose to the screen (me) might suggest.

Good luck with it.
ted
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