Just looking for a little guidance about making my projector screen

nightrider1470

nightrider1470

nightrider1470

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I have ordered some screen material for a 2.35.1 screen. Have ordered enough to make 9ft in length for my 9ft wall, all though I plan to go under this size as have large floor standing speakers I want at each side of the screen.

My main question is!!...... Is it best to install the projector center of the screen (I do have lens shift) and project a certain movie I know is in 2.35.1 format, Gladiator?, measure projected image on my screen and build my frame the exact size!, would that be the best way to go about it?, or should I max zoom a 16.9 movie? CONFUSED!!

I have a throw of around 12.5ft and I have a Optoma HD87 projector
http://www.projectorcentral.com/Optoma-ThemeScene_HD87-projection-calculator-pro.htm

I also own a Lumagen 3Dmini which I would like to use for scaling the image when in 16.9 format.

Am just confised what is the best way to go about getting it right first time

Thanks so much!!
 
You can build a 2.35:1 screen, but you'll have to zoom out when you want to watch 16:9 content. Or, you can build a 16:9 screen and have black bars with 2.35:1 content. I'd personally go for the second option (many cinemas do this rather than using variable aspect ratio screens now).
 
Build a 16:9 screen and mask it to 2.31:1 when you watch content at that aspect ratio.

Most projectors should let you shift the image to the top if it's a different aspect to the panel so you don't have to mask top and bottom.
 
None of the people replying understand about constant image height (CIH) projection. They've only ever experienced constant image width projection where the best quality image (BD movies) ends up as the smallest area picture.

You shouldn't really need to project to set the screen dimensions. The maths is straightforward. All you really need to decide is whether you go for 2.35:1 or 2:40:1 aspect ratio. The film industry uses "2.35:1" as a catch-all. The movies might have been shot 2:40 or wider. You'll find lots of films are 2.40:1 when transferred to BD or DVD. In practise it makes very little difference for home projection. A 9ft wide 2.40:1 screen is 108" x 45". A 9ft wide 2.35:1 screen is 108" x 45.97". Personally. I'd go with 2.40:1

If your concern is image size vs throw distance, then whether it's 16:9 or 2>40:1 makes no odds as far as the projector is concerned. The widest image possible is where all the DLP panel is used. Put up a white test pattern or something light. Zoom out to the max extent. Make sure that any edge cropping is switched off. Then focus the projector lens. That will show you the maximum image width from the projector position. Since your screen will have thickness by the time it is mounted, the actual image size will shrink by a tiny fraction.

Make sure you build black borders for your screen. Velvet is good. Buy skirting architrave with an appropriate profile and then use contact adhesive to glue the material. It'll pong a bit but that's just the solvents dispersing. It'll be fine after a couple of days.

For those interested, Nightrider1470's movie scoped image will be substantially bigger when projected this way. There's more info here
 
Thanks Lucid!!

2.40:1 seems much better then.

Could you work out the maths for a 7.5ft and 8ft 2.40.1 screen as it will be one of those sizes.

I just hope there is enough Zoom on my projector to zoom the black bars from 16.9 content.

I have been told to zoom a 16.9 image to fill the 2.40:1 screen then use my lumagen 3Dmini to downscale the image when a cinemascope movie plays. Not sure if that makes sense to you :)
 
lucid said:
None of the people replying understand about constant image height (CIH) projection. They've only ever experienced constant image width projection where the best quality image (BD movies) ends up as the smallest area picture.
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I understand the concept, and also know that it's not possible without changing the zoom of the projector. As the Optoma is manual zoom and manual focus then it's important to weight up whether you want the hassle of refocusing the unit whenever you change aspect ratio of your content.

Also doing what's written in AlecR's first sentence would achieve a constant image height.

I wouldn't downscale a 16:9 image to fit the screen height on a projector focused for a wider screen because you'll lose a lot of resolution doing this. However if you try it and you can't tell the difference then it's easier than messing around with the lens each time.
 
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I'll tell you how to do the maths and then you can do calculations on any screen width you want.

The aspect ratio of the screen is 2.40:1 That means for every 2.40 inches of width means 1 inch of height. So you're using the times button or the divide button on your calculator.

Screen width divided by 2.40 = screen height.

Convert feet in to inches first to make things simple. So our original 9ft wide 2.40:1 cinema screen measures 108" from side to side. 108"/2.40 = 45"


I believe you're overthinking the whole zoom/aspect/Lumagen thing. It's really quite straightforward if you follow my steps.


1) Get a DVD or Blu-ray disc that is 16:9 i.e. it fills the entire screen area of your TV when the TV is set to 16:9 mode. Try a Pixar animation. They're nearly always 16:9 on the disc. Now go find a film that is 2.40:1

2) Put your projector where it's going to be installed. Set the ZOOM to the BIGGEST picture size. Play that 16:9 DVD/Blu-ray DIRECT into the projector and make sure the projector is on 16:9 mode. DO NOT go via the Lumagen at this stage.

The image you have projecting on to the wall is the biggest image your projector can make. The WIDTH of this image is the WIDTH of your 2.40:1 screen. Mark out the left and right image edges with some tape.



3) Swap the disc for the 2.40:1 film. The image should still fill the width between the tape marks, but it won't be as tall. This is your 2.40:1 screen height. (shown in the diagram by the black outline) if you want to mark the top and bottom edges with tape then go ahead.



If you left your setup like this then any 16:9 or 1.85:1 film would overspill the top and bottom edges of your screen. But you're not going to do that because you have a Lumagen scaler. You'll only use the full area of the screen for letterboxed Blu-rays and DVDs (or rips), so your image will look like this...



4) Now wire in the Lumagen. Play the 16:9 movie again. Set a custom aspect ratio in the Lumagen so that the 16:9 movie fills the height of the screen. The aspect ratio of the film as projected needs to be 16 units of width to 9 units of height. Measure the image height. Divide that figure by 9, and then multiply by 16. This tells you how wide the image should be. If the Lumagen has individual controls for width and height then you can adjust the width so it meets the correct size.



You need do nothing with the projector when playing movies and TV. Just switch the Lumagen between it's standard setting which is what you'll use for letterbox (2.35 or 2.40) movies, and the custom ratio for 16:9 movies and TV.
 
Caged said:
I understand the concept, and also know that it's not possible without changing the zoom of the projector. As the Optoma is manual zoom and manual focus then it's important to weight up whether you want the hassle of refocusing the unit whenever you change aspect ratio of your content.
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With respect, if you understood CIH a little more then you'd know that the next stage beyond re-zoom & re-focus of a manual projector is to use a scaler to do exactly what nightrider1470 is planning.

Yes, granted, without a scaler or lens memories a la JVD DiLA's etc then you have to manually zoom and refocus. But since he already said he has a scaler, and posted that in the OP and once further in direct response to the zooming question and all at least an hour before before your reply I just quoted, then I presume your knowledge only goes so far.

Caged said:
Also doing what's written in AlecR's first sentence would achieve a constant image height.
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Well, since AlecR's first suggestion is exactly what nighrighter1470 is planning anyway (minus the part about zooming) then what's your point? He's just telling nightrigher1470 the same as what he's already planning to do.

AlecR's second suggestion in that post is a 16:9 screen, so basically the opposite of CIH; it's a CIW solution.

Caged said:
I wouldn't downscale a 16:9 image to fit the screen height on a projector focused for a wider screen because you'll lose a lot of resolution doing this. However if you try it and you can't tell the difference then it's easier than messing around with the lens each time.
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Of course, and that's your choice.

The way I look at it is in comparison to a 720P projector. The maximum full panel area at 720p 16:9 is 0.92 megapixels. Compare that to a 16:9 scaled window in a CIH system when using 1080p projector as planned here. The resolution of that 16:9 window is 1.13 megapixels. That's 23% more resolution than we've been used to for the last 10 or so years with 720p.

I'd agree about the potential loss of light. But since digitals have good ANSI brightness, then a small portion of the image is just as bright per square foot as it would be if the entire panel carries an image. The real issue is the blackness of the unused portions of the panel: Will they create a glow around the image? Well, since this is a fixed screen rather than a motorised then we can presume that the room isn't your standard domestic living room with a telly in the corner. So it's probably safe to say that there's a bit more latitude for sympathetic paint schemes to help reduce the effects overspill.

Over all I'd say that the scaler solution is the best compromise before going for a lens memory projector or the expense of an anamorphic prism or lens.
 
lucid said:
With respect, if you understood CIH a little more then you'd know that the next stage beyond re-zoom & re-focus of a manual projector is to use a scaler to do exactly what nightrider1470 is planning.
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The only thing I don't understand about CIH is how such a horrible way of dealing with differing aspect ratios has been given a name and presented as some sort of acceptable option. It trades resolution, overall image brightness and the size of a 16:9 image for the questionable benefit of having 2.40:1 content show at the same height.
 
Caged said:
The only thing I don't understand about CIH is how such a horrible way of dealing with differing aspect ratios has been given a name and presented as some sort of acceptable option. It trades resolution, overall image brightness and the size of a 16:9 image for the questionable benefit of having 2.40:1 content show at the same height.
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I thought you said you understood CIH?

There are several different ways of dealing with CIH. Some have no significant compromises at all; near-enough the full panel resolution is used both in 2.40:1 and in 16:9 modes. The rub is the cost.

The lens zoom option is the next best choice. After that it's a scaled option. All are CIH. What's difficult to understand?

If you saw the difference in image size watching a 2.40:1 letterboxed on a 16:9 screen, and then shown on a 2.40:1 screen you'd understand immediately what the benefit is. If one can accommodate it, why have your highest quality source image displayed any other way?
 
I understand there are several methods of retaining the height of a projected image whilst changing the width. Really, I get it.

What I don't understand is that seeing as the constraint on screen size is the width, why you'd choose to set a system up for 2.40:1 by masking the top and bottom of the image, and then mask the sides to show 16:9 content. You could just as easily mask the top and bottom of the 16:9 image when you're showing 2.40:1 content and then remove them to show content at 16:9.

It's clear that the priority of people who set systems up this way is to keep the height of both formats the same at the expense of everything else, I just can't understand why anyone would make that choice - it doesn't make your 2.40:1 image any bigger, it just makes 16:9 smaller.

Now if we were talking about blending two projectors to get to 2.40:1, masking it to 16:9 and centering the content that would make perfect sense. Doing it the way it's been described is like masking off the top and bottom of your TV because you like 2.40:1 movies and then scaling everything else to fit that new height.

lucid said:
If you saw the difference in image size watching a 2.40:1 letterboxed on a 16:9 screen, and then shown on a 2.40:1 screen you'd understand immediately what the benefit is. If one can accommodate it, why have your highest quality source image displayed any other way?
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This bit specifically doesn't make sense. If you have a fixed installation point for a projector and a 16:9 screen that is as wide as the projected image can go, and then replace it with a 2.40:1 screen at the same width it's not making your 2.40:1 image any larger. Obviously when you're talking about diagonal sizes then yes a 100" diagonal 2.40:1 screen will show that format larger than a 100" 16:9 screen would, but I've never come across anyone who specifies projector screens as diagonals because it makes doing the throw calculations more difficult.
 
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You clearly don't understand CIH. The 2.40:1 screen is NOT the same width as a 16:9 screen. It is WIDER. That's the whole point.

Imagine a screen 100 cm tall. If it was a 16:9 screen then it would be 178cm wide. If is was a 2.40:1 screen then it would be 240cm wide.

Now here's the maths bit, so hang on to your hat.... 240cm take away 178cm equals drum roll please... 62cm.

So the 2.40:1 screen material is the same height (100cm) but it is a total of 62cm wider than the 16:9 screen material. Obviously (he says in hope???) you understand that the 62cm is equally split left and right of the screen. So for the same 100cm screen height there's and EXTRA 31cm of white material on the left and right sides beyond where a conventional 16:9 screen finishes. It's wider for the same height.


Now lets look at what happens with typical images. To keep your head from exploding let's just say that both screens are 100cm tall. The pictures are in proportion to each other - they are to scale, okay?

Here 16:9 TV on a 16:9 screen versus the same picture on a 2.40:1 screen.




Now let's look at letterboxes movie images as you'd get on Blu-ray. The screen sizes are as above. The images are still to scale




Do you see how a the people in the 16:9 screen are smaller compared to the ones on the 2.40:1 screen. That's because a 16:9 screen is effectively a Constant Image Width system.

With the 2.40:1 screen the projected image is the same height whether it's a 16:9 TV/film or if it's a letterbox film. What changes is the width of the image. That's what Constant Image Height means.



Surely you must get it now? If not, then please give up because you'll never ever get it.
 
You can't read. Everything you've written is correct, but it doesn't answer my post at all. It doesn't matter how much sarcasm you add or how patronising you want to come across - you're arguing against I point I never made.

I'll try to make it even clearer. I 100% understand that doing what you're doing gets both images to take up the same amount of vertical space. I promise you, I understand that. Even before your pictures. Even before this thread was written. I'm not questioning that. I'm questioning why you would want to limit the vertical height (and therefore overall size) of 16:9 content to the height of 2.40:1 content when your projector is capable of a lot more.
 
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And that's still because you're thinking 16:9 as the biggest possible screen format.

CIH started life in cinemas. All 35mm cine film is inherently 4:3. So all movies up to the early 50's were 4:3 too. When TV started to have a significant impact on cinema attendance numbers the film studios looked for an edge with which to fight back. They started to experiment with more extreme aspect ratios. There were lots of different versions. Some used larger negative sizes and simply cropped the image. Other's used an aspherical lens to distort the light passing through it so that the film negative received a vertically stretched image. This was then corrected by at projection with a lens that did the reverse process.

The optical distortion system is used in the full fat implementation of CIH. A scaler or a special projection processing mode stretches the letterbox signal so that it fills the the 16:9 imaging panel(s) inside the projector. An anamorphic lens then stretches the image width so that it fills a 2>40:1 screen. When 16:9 is required then the lens slides out of the way.

So in answer to the question "why you would want to limit the vertical height (and therefore overall size) of 16:9 content to the height of 2.40:1 content when your projector is capable of a lot more."

i) it's not "limited". The 16:9 image height can be the same as it would be with a 16:9 screen. What's different is that 2.40:1 is bigger rather than smaller as you get with a 16:9 CIW system.

ii) The implementation of CIW depends on the hardware available. I've already detailed the three methods. nightrider1470's solution uses a scaler and crops the panel resolution for 16:9. That's an acceptable trade-off to get a 2.40:1 image that is 82% larger than it otherwise would have been be on a 16:9 screen of the same image height.

iii) What's your best quality source? It's Blu-ray movies. So, as detailed before, doesn't it make sense to have a screen that suits the shape of your best quality image, and a picture size that makes the most of your best quality image? Isn't that the whole reason for having a home cinema system in the first place.


Now let me turn it round on you. Why would you want your lowest quality source material (16:9 TV) to be bigger than your highest quality source material?
 
I think we need to set some constraints, namely that we're dealing with a 16:9 projector and no anamorphic lenses, which is what the projector in question is. We also need to accept that there's no lens zooming happening between the picture modes.

With that said, you're still looking at this wrong. It's impossible to get a 2.40:1 image out of a 16:9 projector that is larger than a 16:9 image coming out of the same projector.

Now, if you have a 100" wide area of wall to fit a screen, and you put in a 16:9 screen and projected a 2.40:1 image onto it, it would be exactly the same size as if you filled that 100" wide gap with a 2.40:1 screen. The only difference is there would be excess screen at the top and bottom, which you mask off.

By trying to do constant image height on a 16:9 projector you have to mask off pixels when you want to show a 2.40:1 image and then you have to mask off more when you want to show a 16:9 image. If reducing the 16:9 image to the same height as a 2.40:1 so that they match is the most important thing about your projected image then that's great, but I don't see why you'd do that when you could opt to use the full panel to show the 16:9 content.
 
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I have no experience with projectors, but this discussion has me confused!

I think what Caged is saying Lucid, is that in your example above, you're limiting the height. As the OP has a 9' wide screen, this is the restriction. A 16:9 image can get larger on a 9' wide screen once the 2.40:1 image has reached the maximum width. ergo, why not project 2.40:1 on a 16:9 screen?

I think that's the gist anyway. I'm not arguing either way, but interested in your reasoning :)
 
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