2.35 Constant Height Faq

After reading many of the same questions being asked I thought it would be a good idea to have one main thread that discusses the main ideas of a constant height setup.

This article will deal with constant height info.

Feel free to add anything I missed as I'll keep updating this main post.

WHAT IS IT?

What is a 2.35 Constant Height Setup?

In basic terms, its the ability to watch 2.35 material in full resolution and with full width just as the director intended. In a constant height setup 2.35 movies take up the whole screen without any black bars above/below. This a good read to get a better idea of constant height: http://resmagonline.com/articles/pub...icle_774.shtml

What benefit does constant height provide over a normal 16x9 setup?

Because you are using the projectors full panel to display the 2.35 image, there is a 33% increase in resolution. The light output is also about 20% more than the same size picture without an anamorphic lens.

This results in a smoother more film like image that has alot more depth and punch to it.

Some other benefits of constant height also include more immersion for 2.35 films due to the extra width and no more annoying black bars. And also easier masking options.

HOW?

How does it work?

http://www.avsforum.com/avs-vb/showthread.php?t=830657

This link shows in a visual sense how a 2.35 constant height setup operates:
http://www.prismasonic.com/english/intro.shtml#2

http://www.panamorph.com/index.html See "How it Works" Box

WHAT DO I NEED?

What equipment do I need to run a constant height setup?

Here's a link that has some of the products that can be used for constant height: http://www.avsforum.com/avs-vb/showthread.php?t=537491

1. 2.35 programming

Movies/tv shows/dvd's and even trailers. Anamorphic enhancement preferred. Look out for HD 2.35 clips/movies in the future.

2. A 16x9 native projector

Although using a 16x9 projector with a lens is the ideal method for optimal resolution, it is just as possible to establish a constant height arrangement with just a 16:9 projector and no anamorphic lens and zooming (or a 4:3 projector with anamorphic lens and zoom) so long as you are comfortable with not using all of the projector's available pixels/brightness.

Projector/Lens Compatibility

3. Scaler that performs the required vertical stretch

This can either be built into the projector, dvd player, standalone scaler units or HT/Media Centre PC's. All you're after is the pre-lens vertically stretched image. Note though, that alot of projectors limit the options for changing the aspect especially when inputting upscaled DVD images.

Standalone scalers and HTPC's will generally provide more flexibilty.

4. 2.35:1 Screen

This means the screen is 2.35 units wide for every 1 unit high. Normal 16x9 screens are 1.78:1 ratio.

Most of the screen manufactures can produce a 2.35 ratio screen. DIY options are also possible. Again, all you're after is the 2.35:1 ratio.

The optimal screen for the true cinematic experience would be an acoustic sound screen that's transparent. This allows all front three speakers to be placed behind the screen with sound coming directly from the screen. Again, most manufactures provide this option. DIY solutions also exist, with Dazian Celtic Cloth and SMX (SandmanX) 720 being the most popular.

5. Anamorphic lens (Horizontal stretch or Vertical squeeze)

There are two ways to reach the final goal of constant height - Horizontal stretch lens or Vertical squeeze

Some may want to remove the lens for movies with ARs less than 2.35 in order to maximize the number of display pixels used. In so doing, there are a few things to bear in mind.

A situation occurs when removing a vertical squeeze lens that does not happen when removing a horizontal stretch lens. The displayed picture becomes too tall for the screen. That is assuming the screen AR matched that of the PJ and lens system. In that case the PJ zoom function must be employed to shrink the displayed pictured -- Hmm, scaling with a lens again. This time however the shrink occurs equally in both dimensions - isotropic scaling. The Pj would have to be capable of a zoom ratio of at least 1.322 : 1 , assuming the lens had a compress ratio of (16/9) / 2.35

A way of thinking about this is that the vertical squeeze lens does not affect the throw distance whereas a horizontal stretch lens decreases the throw.

Additionally, depending on the specific lens (either type) and projector, lens offset can enter into the mix and require additional adjustments. Some anamorphic lenses shift the position of the displayed picture vertically.

And finally, some projectors may shift the vertical position of the center of the picture when zoom is invoked as well.

Which Anamorphic lens is right for me?

http://www.avsforum.com/avs-vb/showt...ght=Anamorphic

http://www.prismasonic.com/english/specs.shtml Horizontal/ Vertical with option of motorized
http://www.panamorph.com/Products.html Vertical or Horizontal
http://www.isco.eu/index.php?id=home-cinema High end lens with option of motorized
www.cineslide.com Manufacturer of Isco lens transports, USA distributor for ISCO lenses

How Anamorphic lens technology works

How the different lenses work

http://www.panamorph.com/Technology.html

SCREEN MASKING?

Manufacturers that sell Screen Masking for 2.35

What happens to sides of the 2.35 screen when I watch movies with less width (1.78/1.85 etc)?

You mask/cover up the sides of the 2.35 screen when you watch movies that aren't as wide as 2.35. Just like the real cinemas. Ever wondered why the movie screen widens for some films when you go the cinemas. Now you know. To maintain the height necessary for 2.35 movies the width must increase. Hence the term constant height.

A fellow member posted this:

"As with any fixed pixel display, when you need to map a non-native aspect ratio into the panel you will not use all of the pixels. Since the lens in this case transforms the 16:9 projector into a 2.35 projector any ratio other than this will result in either pillar boxing or letter boxing. For ratios greater than 2.35 this would be letter boxing (constant width). And of course this means anything less than 2.35 would have black bars on the sides, which is constant height"

How do I figure out how much I need to cover up?

The great thing about constant height is you only need to mask the sides of the picture. To figure out how much you need to mask when you watch movies with less width than 2.35 you multiply the screen height (which remains the same for all movies aka constant height), by the aspect ratio of the movie.

So say you watch a 1.78:1 ratio movie. For a screen 50" high you multiply it by 1.78. Hence the 1.78 units wide for every 1 high.

So 1.78 x 50" = 89"
1.85 x 50" = 92.5"
1.33 x 50" = 66.5"

As you can see a 1.78 movie is 89" wide out of the possible 117.5" for 2.35 movies. 2.35 movies of course don't need masking as they take up the whole width.

A very limited number of films are shot in ratios wider than 2.35 eg. Ben Hur. You can either live with the small black bars top and bottom, stretch the image so it fills the 2.35 screen or if you're totally obsessed mask the top and bottom. This would mean you would need a 4 way masking system.

What do I do with the anamorphic lens when I want to watch non 2.35 (scope)films?

There are a few ways to go about this.

1. Leave the lens in place all the time for all aspect ratios. This implies a loss in resolution and brightness for anything other than 2.35 films as the sides of the picture are now wasted on black pillar bars. A few on this forum leave the lens in place and don't notice any PQ loss as full vertical resolution is still used for all ratios.

One thing to take note of though with brightness is that because the 16x9 image is smaller in area to the 2.35 image, it requires less light to appear as bright as the 2.35 image. Therefore leaving the lens in place means that the brightness should be perceivable the same between 2.35 and 16x9.

The brightness drop occurs if you compared a 1000 lumen 16x9 image with no lens compared to a 500 lumen image with the lens. The areas are the same but the 1000 lumens is brighter as more light is covering that area.

So by keeping the lens in place you shouldn't notice difference in brightness between a full width 2.35 image and a 16x9 image with black bars on the sides.

2. Slide the lens out of place for non 2.35 movies. This uses full resolution/brightness for all aspect ratios. This can sometimes cause the picture to drop depending on the lens.

3. Leave the lens in place but use the passthrough mode that some lenses have (prismasonic range). This involves leaving the lens in place like option 1 but using the passthrough mode on the lens which means not stretching it horizontally and just letting the projected light 'passthrough' the lens unaltered. This like option 2 uses full resolution/brightness for all aspect ratios (2.35/16x9).

How a passthrough lens works.



WHAT ABOUT CONSTANT WIDTH/AREA?

Constant Width is for those who can only accommodate a 16x9 screen. The width remains the same but the height changes. It still uses the full panel of the projector for 2.35 films but you dont get the extra width benefits for scope films. Only a vertical squeeze lens works for this application as you take the vertical stretched 2.35 picture and squeeze it down vertically to correct the geometry.

To find out more check out 'The 16:9 Screen Option' a little down the page: http://panamorph.com/Ultimate235.html

What about this Constant Area methology that everyone's talking about?

The idea behind Constant Area is that every aspect ratio has same/similar area. This means that every aspect ratio appears large as the brain perceives size in how much area an object has not in width or height. The screen ratio for constant area is 2.05 which is halfway between 1.78 and 2.35.

Here's some links that go into more detail:

http://archive.avsforum.com/avs-vb/s...threadid=15649
http://www.videophile.info/Screen/Page_01.htm
http://www.mindspring.com/~zyber/cinema-screen.html


Where can I see some 2.35 Constant Height setups in action?

2.35 Picture Thread
Jeff Leonard
Willy Gib
Alan Gouger
Gary Lightfoot

Additional reading:

http://www.brooklyncenter.com/cinema...inemascope.htm
http://www.thecinemalaser.com/anamor...pport-page.htm
http://www.thedigitalbits.com/articl...hic/index.html
http://www.thedigitalbits.com/articl...reenorama.html
http://www.avsforum.com/avs-vb/attac...chmentid=39384

If I've missed anything please tell me and I'll add it on.

Yes that sounds correct.


Yes the AE700 will do the required vertical stretch. There's only a handful of projectors that will do this.

Yeah true, upscaled I dont think works.

This is very true. I'll add that comment to the post. The point of the FAQ was to answer some of the basics of constant height for new comers. Alot of the same questions kept popping up in this forum.


Thanks Shawn, I added that link to the top.

I'd love to add it but dont know enough about the mechnics of it. If you or someone else would like to write a summary about constant area please do so and I'll add it in.

This is the only info I have about it. http://www.videophile.info/Screen/Page_01.htm

Ted and Josh, thanks I added those links in. I'll keep adding to constant area as I get more info.

jamin , thanks for the input. I updated that section with your feedback. Please check to see if its correct now.

As I understand it when you put a anamorphic lens in front of a 16x9 projector, the projector is now a 2.35 projector. So as you said anything smaller than the projector ratio (2.35 with lens on) has black bars. With a horizontal and vertical lens this occurs. The way around it with a horizontal lens is passthrough or remove the lens. This inturn now makes it a 16x9 native projector. Removing the vertical lens also makes it a 16x9 projector again but as you said it's too tall. So zooming is required.

So the best and simplest way to get full resolution for 16x9 and 2.35 is use a horizontal lens. This means passthrough can be used and no zooming is required.

But you're right, both vertical and horizontal will work. Vertical just needs more effort to setup each time if you want the best PQ for all ratios.

Did I write anything incorrect in the faq?

Jamin, Thanks for the link. I added it to the post.

With regards vertical lens stuff we were discussing, would you mind writing a couple of paragraphs and I replace mine with what you write. This should clear alot of it up.

Thanks jamin, I replaced mine with what you wrote.

About a 20% increase between a zoom/letterboxed 2.35 image and one with the lens that uses the full panel.


There may be. I dont know enough about that to give you a decent answer. Maybe do a search on here to see how others mount theirs.


I dont have a constant height setup yet but from what I've read for seating distances, about 1.2-1.3x for 2.35 images were what most were using. Its up to personal preference really so maybe try it on the wall first to see the size. Or if you can move seating then you have a bit of leeway.