Consequences of exceeding specified throw distance. - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 5 Old 05-25-2020, 02:00 AM - Thread Starter
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Consequences of exceeding specified throw distance.

I'm looking for feedback on exceeding manufacturer published specifications for Throw Distance on Ultra Short Throw projectors. What dictates that maximum image size number?

I am projecting to a 270 degree curved screen in a flight simulator and would like to be able to use an 11.5 ft tall screen. There are obstructions that mandate the short throw. I understand loss of brightness, but I have a light controlled environment, and there are very bright Ultra Short Throw projectors like the Epson LS100. I expected that sharpness would degrade, etc. Can I get away with it?

The best setup I can find that stays in manufacturer specs is something like Optoma GT1080Darbee/GT1090HDR sort of projectors that list ~300" diagonal image output, but these are 0.5 throw ratio and I'd like to use one of the 0.25 projectors, but these have smaller image output specs.

Many thanks for any feedback!
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post #2 of 5 Old 05-25-2020, 06:15 AM
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Have you tried any kind of projector on your curved screen? All projectors that I am aware of are designed for a flat screen. First you will need a projector that a lot of grid point adjustment to eliminate the barrel distortion. Using a UST projector is going to compound this issue and exceeding the manufactures screen size is throwing another monkey wrench into the mix. I doubt you will get much help here as most of us are HT fans.

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post #3 of 5 Old 05-25-2020, 08:37 AM
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Quote:
Originally Posted by 8KCABrett View Post
I'm looking for feedback on exceeding manufacturer published specifications for Throw Distance on Ultra Short Throw projectors. What dictates that maximum image size number?

I am projecting to a 270 degree curved screen in a flight simulator and would like to be able to use an 11.5 ft tall screen. There are obstructions that mandate the short throw. I understand loss of brightness, but I have a light controlled environment, and there are very bright Ultra Short Throw projectors like the Epson LS100. I expected that sharpness would degrade, etc. Can I get away with it?

The best setup I can find that stays in manufacturer specs is something like Optoma GT1080Darbee/GT1090HDR sort of projectors that list ~300" diagonal image output, but these are 0.5 throw ratio and I'd like to use one of the 0.25 projectors, but these have smaller image output specs.

Many thanks for any feedback!
Curved screens inherently introduce barrel distortion in an image as a result of the change in focus distance coming from a lens.

Because of this, curved screens are often used in conjunction with an anamorphic lens to offset the inherent "pincushion" distortion introduced with its use to display "scope" type aspect ratios.

With "Pincushion" distortion, the corners of the image of a square are farther from the center than the middle part of the sides, making the image appear pinched in the middle. Or, straight lines are curved outwards from the center. A curved screen can offset this by bringing the outside edges of the screen closer to the lens.

"Barrel" distortion is just the opposite with straight lines curved inwards from the center in the shape of a barrel. There are some anamorphic lens designs that will produce "barrel" distortion and in which case, the use of a curved screen would/could result in a doubling of the distortion.

A 270° curved screen is quite a bit of curvature but is also quite common for use in flight simulators. Because of the this amount of curvature, it's necessary to use multiple projectors and blend the image edges to cover the screen area to overcome distortion and maintain focus. Typically, three projectors are necessary and many modern simulators are using 6 or more projectors. Much of this technique has its roots in what was called Anamorphoscope first developed in 1926 and what we know today as CinemaScope from the 1950's-60's.

The direct answer to your question is that the maximum image size from the manufacture for a given projector is based on a minimum amount of image brightness for viewing. On these short throw projectors or any projector for that matter, it's possible to simply move the unit further away from the screen and increase the image size if the lens zoom function is at its limits. The downside is whether or not the units lamp will produce sufficient brightness as to be acceptable. You're simply spreading the available light over a larger area and the perceived brightness will be reduced. Light from a point source behaves and is subject to the inverse square law in physics. Lens focus properties will remain the same however, the perceived sharpness maybe less with the reduced brightness.

As for your curved screen with a single projector, expect to see some focus issues and vertical/horizontal distortion as you increase image size along with a drop-off in brightness.

Again, the solution with this amount of screen curvature is the use of multiple projectors.
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post #4 of 5 Old 05-25-2020, 03:37 PM - Thread Starter
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Thanks for that detailed reply. I guess I owe an apology that perhaps my post wasn't clear. I know this is a multi projector setup, I built a 9.85ft radius, 10ft tall 170 degree flight simulator with a full size 5 seat airplane fuselage in it, and had to put three GT1080Darbees in portrait mode (which results in a very strange projector placement and angles to the screen. I'd like to move to a 270 degree arc, and get the projectors horizontal above the fuselage. Right now it looks like I need 5 projectors and a larger screen radius to do this with the 0.5 throw ratio GT1090HDRs. The larger radius effectively reduces the vertical field of view, when I need to increase it, this is why I want to reduce the screen radius. If I get a shorter throw ratio projector array, I have fewer shadowing issues from the fuselage.
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post #5 of 5 Old 05-26-2020, 07:05 AM
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Quote:
Originally Posted by 8KCABrett View Post
Thanks for that detailed reply. I guess I owe an apology that perhaps my post wasn't clear. I know this is a multi projector setup, I built a 9.85ft radius, 10ft tall 170 degree flight simulator with a full size 5 seat airplane fuselage in it, and had to put three GT1080Darbees in portrait mode (which results in a very strange projector placement and angles to the screen. I'd like to move to a 270 degree arc, and get the projectors horizontal above the fuselage. Right now it looks like I need 5 projectors and a larger screen radius to do this with the 0.5 throw ratio GT1090HDRs. The larger radius effectively reduces the vertical field of view, when I need to increase it, this is why I want to reduce the screen radius. If I get a shorter throw ratio projector array, I have fewer shadowing issues from the fuselage.
Then you clearly understand the problems with your practical experience.

I would not expect any UST unit to behave any different than the GT1080 units subject to their own or any limiting factors in hardware.
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