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# Curved screen dimensions? Keeping same aspect ratio?

I am building a curved screen and have calculated that for an aspect ratio of 2.35:1. Problem is that when you curve the screen the aspect ratio reduces, in my case it drops to 2.32:1 and the actual screen dimensions being 69" high by 160" wide with a 40' radius.

I want to know if it is possible to widen the screen to 165" with the 69" height remaining the same so I can have an aspect ratio of 240:1? Or does the curved screen mean that movies that are 240:1 will fall short on the sides of the screen?
Quote:
Originally Posted by JapanDave

Or does the curved screen mean that movies that are 240:1 will fall short on the sides of the screen?

The curve will provide a sort if optical compression effect. Also to consider is the fact that the cylindrical anamorphic lens may increase or decrease the final width depending on the throw and the final position of the front lens after astigmatism correction is dialed in. Shorter throws for example produce a wider image than longer throws.
Quote:
Originally Posted by CAVX

The curve will provide a sort if optical compression effect. Also to consider is the fact that the cylindrical anamorphic lens may increase or decrease the final width depending on the throw and the final position of the front lens after astigmatism correction is dialed in. Shorter throws for example produce a wider image than longer throws.

It will be a short throw of 4.6m for 175cm high screen. So I guess it will produce a wider image.

What do you mean by "optical compression effect"?
Quote:
Originally Posted by JapanDave

It will be a short throw of 4.6m for 175cm high screen. So I guess it will produce a wider image.

So a TR of 1.47:1. I don't see a problem.

Quote:

What do you mean by "optical compression effect"?

If you were to fire up the projector and move a sheet (substituting as a screen) in the light path, you would notice that as you move it in closer to the projector, the image decreases in size, as you move it away, the image gets bigger.

Basically, because the screen edges of a curved screen are closer to the projector than the centre, the image is progressively reduced towards the edges. This is why it corrects pincushion. As a bi-product, it also reduces the width progressively as well. According to a certain optics expert, this is why I see no GD on my screen. So apparently, having optics with multi-aspheric radii has nothing to do with it
Slightly off topic, but still kind of on topic:

Mark, your MKIV will work with TR down to 1.4 is this correct? Also, when lens companies say that the lens works down to a certain TR, do they mean that if you go any smaller then you will experience vignetting? Also, how do they take into account how big the image is coming out of the PJ, reference the PJ's lens zoom, compared to the TR in order to rule out vignetting?

Sorry if this was a slight hijack on Dave's thread, but maybe it can help him as well. Thanks!

-Sean
Quote:
Originally Posted by JapanDave

I am building a curved screen and have calculated that for an aspect ratio of 2.35:1. Problem is that when you curve the screen the aspect ratio reduces, in my case it drops to 2.32:1 and the actual screen dimensions being 69" high by 160" wide with a 40' radius.

I want to know if it is possible to widen the screen to 165" with the 69" height remaining the same so I can have an aspect ratio of 240:1? Or does the curved screen mean that movies that are 240:1 will fall short on the sides of the screen?

Can't you overshoot 2.4 content on the sides? It would about 1.5" on each side at these dimensions.
Quote:
Originally Posted by 230-SEAN

Slightly off topic, but still kind of on topic:

Mark, your MKIV will work with TR down to 1.4 is this correct?

Correct and a claim I was able to make after installing one at that TR. Projector pending, I would say 1.3:1 in possible with the MK4.

Quote:

Also, when lens companies say that the lens works down to a certain TR, do they mean that if you go any smaller then you will experience vignetting?

Again projector pending. If you are using a projector with a really recessed lens, then you can't expect to achieve the same results as a projector with a flush lens.
Quote:
Originally Posted by CAVX

So a TR of 1.47:1. I don't see a problem.

If you were to fire up the projector and move a sheet (substituting as a screen) in the light path, you would notice that as you move it in closer to the projector, the image decreases in size, as you move it away, the image gets bigger.

Basically, because the screen edges of a curved screen are closer to the projector than the centre, the image is progressively reduced towards the edges. This is why it corrects pincushion. As a bi-product, it also reduces the width progressively as well. According to a certain optics expert, this is why I see no GD on my screen. So apparently, having optics with multi-aspheric radii has nothing to do with it

Thanks.

I realize why it corrects the pin cussion, I just could not get my head around what the outer edges of the beam will be doing. I have got now, cheers.

Quote:
Originally Posted by dukeav

Can't you overshoot 2.4 content on the sides? It would about 1.5" on each side at these dimensions.

B/c I don't want to lose the width, I want the widest image that is there to be viewed.
Quote:
Originally Posted by JapanDave

B/c I don't want to lose the width, I want the widest image that is there to be viewed.

And ultimately, that will depend on exactly where the front lens sits after astigmatism is corrected in the MK4. On my current curved 2.37 screen, I have slight pillars at my TR of 2.1:1. At a closer TR, that would change where the image would be slightly wider.
Quote:
Originally Posted by CAVX

And ultimately, that will depend on exactly where the front lens sits after astigmatism is corrected in the MK4. On my current curved 2.37 screen, I have slight pillars at my TR of 2.1:1. At a closer TR, that would change where the image would be slightly wider.

With that in mind, I am going to make my screen 2.40:1 for sure.
Quote:
Originally Posted by JapanDave

With that in mind, I am going to make my screen 2.40:1 for sure.

That should work out nicely then. I look forward to seeing the photos.
I should have them soon.
Quote:
Originally Posted by CAVX

That should work out nicely then. I look forward to seeing the photos.

+1, have fun building and post lot's of build photos and screen shots when done.
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