Curved screens -what's the point? - AVS Forum
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post #1 of 24 Old 04-24-2010, 08:56 AM - Thread Starter
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Several A-lens users, including Art, have stated that pin-cushion distortion is a non-issue when deploying an A-lens. I thought the whole point of a curved screen was to eliminate pin-cushion distortion induced by the A-lens. Seems like I am wrong. So what then is the point of using a curved screen?
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post #2 of 24 Old 04-24-2010, 09:02 AM
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Given the parameters of one's setup - namely lens and throw ratio - the amount of pincushion incurred can require that an unfavorable amount of the image be masked to achieve straight edges. A curved screen will fix this.

Curved screens also help to "focus" more light back at the viewer, thus producing a slightly brighter image than a flat screen made of the same material.

Plus, plenty of screens in theaters are curved, so it adds to that "wow factor."

That's why.

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post #3 of 24 Old 04-24-2010, 09:27 AM - Thread Starter
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Fine. But now what happens with 16:9 on the curved screen? Don't you get barrel distortion and horizontal differential focus issues since the projectors optical system is specifically designed for projection onto a flat screen?
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post #4 of 24 Old 04-24-2010, 11:08 AM
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Quote:
Originally Posted by taffman View Post

Several A-lens users, including Art, have stated that pin-cushion distortion is a non-issue when deploying an A-lens. I thought the whole point of a curved screen was to eliminate pin-cushion distortion induced by the A-lens. Seems like I am wrong. So what then is the point of using a curved screen?

There are 2 main reasons to install a curved screen. The first is to mitigate a short throw, and the second is because some people think they are cool.

I have yet to see one that can offer a perfect focus on both diagonals. There is also the possibility that the outer areas throw light back onto the opposite edges and cause a reduction in intra scene contrast.

I also find them to be visually distracting.

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post #5 of 24 Old 04-24-2010, 11:12 AM
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Quote:
Originally Posted by taffman View Post

Fine. But now what happens with 16:9 on the curved screen? Don't you get barrel distortion and horizontal differential focus issues since the projectors optical system is specifically designed for projection onto a flat screen?

Correct me if I'm wrong but with 16x9 material you would have to keep the lens in place and scale to 4:3. I'm kinda glad I didn't go curved as I have plenty of 16x9 movies which I move the lens out if the way when viewing.

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post #6 of 24 Old 04-24-2010, 08:23 PM
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Quote:
Originally Posted by taffman View Post

Several A-lens users, including Art, have stated that pin-cushion distortion is a non-issue when deploying an A-lens. I thought the whole point of a curved screen was to eliminate pin-cushion distortion induced by the A-lens. Seems like I am wrong. So what then is the point of using a curved screen?

Doesn't Art use a curved screen?

Anyway, yes, a curved screen is for correcting pincushion caused by the anamorphic lens.

If you move the lens out of the light path, yes your images will barrel. The point to consider is that the width of a 16:9 image is not as wide as the Scope screen so therefore the amount of visible barreling is not as bad as it would be if the image filled the screen.

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post #7 of 24 Old 04-24-2010, 08:26 PM
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Quote:
Originally Posted by coldmachine View Post


I also find them to be visually distracting.

That's what I've found with the curved screens I've seen. I could "see" the curve of the screen while watching a movie and for me this detracted.
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post #8 of 24 Old 04-24-2010, 08:57 PM
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Whilst I use a curved screen, I agree that they are not always needed. A-Lens pending, the image can be made to look as good (both H and V lines brought into focus at the same time) on both a flat and curved screen.

If your going to use a curved screen, then the radius should match to actually offset the curvature of the pincushion it is correcting. Mine is thread adjusted, so can tailors to perfectly match.

Now that I have a curved AT screen, I doubt I would ever go back to a flat screen as I don't find the curve distracting at all, have corner to corner focus and perfect geometry.

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post #9 of 24 Old 04-24-2010, 08:58 PM
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Of course the WOW factor is right up there as well when the lights are on

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post #10 of 24 Old 04-30-2010, 05:21 AM
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The "need" or lack of "need" for a curved screen is a combination of factors:

1. Throw distance between screen and lens (short throws, wide screens = problems);
2. Width of the screen with respect to the width of the room (the closer the screen to the room's width, the more points in favor of curved)
3. Relationship between screen width and distance of primary row (or front row) from the screen.

All of the above need be considered. My experience suggests, corner to corner focus need not be a problem. OTOH, I also find in most installations of curved screens the radius of the screen is way too small ... generally by about half of what it ought to be.

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post #11 of 24 Old 04-30-2010, 05:58 AM - Thread Starter
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Dennis,
Is the curvature of the screen determined by just drawing an arc with the projector as the center point, or is it more complicated than that.
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post #12 of 24 Old 04-30-2010, 10:44 AM
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No, it is more complicated than that. It is a function of the lens system, not the projector's location.

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post #13 of 24 Old 04-30-2010, 01:41 PM - Thread Starter
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I imagine that a curved screen severely complicates moveable masking and curtain design, and would raise the cost into the stratosphere level. Not something to be undertaken lightly!
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post #14 of 24 Old 04-30-2010, 07:05 PM
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Well, you imagine wrong...

I built my owned curved screen with powered adjustable masking and curtain system with 10 AR presets.. It was very easy to do, the only unique reqirements are curvable curtain track and 5 or 6 extra idler pulleys.

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post #15 of 24 Old 04-30-2010, 08:42 PM - Thread Starter
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Well that's great Vern. Who is a source for curveable curtain track?
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post #16 of 24 Old 05-01-2010, 12:16 AM
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Quote:
Originally Posted by taffman View Post

Well that's great Vern. Who is a source for curveable curtain track?

Anyone who supplies motorized curtains should be able to offer flexible track.You can also spec pre-formed radii to add to straight sections to deal with corners etc if you need a heavy duty option. Its a very common option with no significant additional cost, if any, involved. Certainly nothing "into the stratosphere level".

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post #17 of 24 Old 05-16-2010, 10:27 PM
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Originally Posted by CAVX View Post

Whilst I use a curved screen

Mark, are the OZTS guys making a curved screen yet? or do you have something else?

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post #18 of 24 Old 05-17-2010, 04:05 AM
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Originally Posted by Elill View Post

Mark, are the OZTS guys making a curved screen yet? or do you have something else?

I actually modded a flat OZTS screen. You can read about what I did in my blog under Going AT. The interesting part is that I found that I had to reverse the frame to prevent it from taking on the same shape as the pincushion and causing the fabric to sag as I flexed. And because I have a full treated baffle wall behind the screen (speakers are rear loaded), I couldn't just re-tension the fabric. This meant that I then had to make a "new" frame for the masking. Maybe if the baffle wall was added after, the fabric could be re-tensioned and reversing the frame could be avoided.

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post #19 of 24 Old 05-17-2010, 03:23 PM
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Cheers, thanks for the link.

I'm a long way off from needing it, so hopefully they'll have something ready/to market by then - I have thought about a DIY one as well - PITA though, even cutting the curves with my mates CNC. Your way looks good.

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post #20 of 24 Old 05-17-2010, 03:31 PM
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Quote:
Originally Posted by Elill View Post

Your way looks good.

I think the key here is rigidity. The bolts top and bottom pass through 70mm x 35mm structural pine. I guess if I was to do this again, I might use a 50mm alloy angle and attach the baffle walls after the screen goes in. At this stage, DIY is the only cost effective method of achieving this.

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post #21 of 24 Old 05-17-2010, 03:58 PM
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Hmm, ok.

I need to look into the shape of the curves, I was thinking we could cut it out of 45mm LVLs, joined in the middle at an angle and then put a fly screen groove in the face of it and fix the fabric to it in that manner......be easier if they just sold us the curved frame

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post #22 of 24 Old 05-17-2010, 04:39 PM
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Quote:
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be easier if they just sold us the curved frame

Yeah and then comes the challenge of finding the right curve for you. OZTS did look into having their frames profiled, however didn't when told that the machines that bend the alloy need 600mm extra at each end, plus, no guarantee that the machines would not crush the extrusion during the bending process. They can sand fill the profile, however still no guarantee of perfection. Then flocking the curved frame is an issue.

So back to the "right curve", you need to be able to adjust the amount of curve and why I have threads top and bottom. If I need more, I just wind the nuts tighter. If I need less, I can back them off.

So whilst TR plays a big part, the actual lens used also contributes as well. So is short, my MK4 seems to exhibit less pincushion than the Mk3 and I am still using the same TR.

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post #23 of 24 Old 05-17-2010, 05:00 PM
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Flat screen it is then!

Something to think about/work on I guess. I'd want a set and forget solution, once in I'd just want it all calibrated and then I dont want to touch it

- budget doesn't extend to Mk4 over Mk3 unfortunately...

Edit: just got an AUD price for SMX screen - Stuff Me! A$7500 for 110" 2.35 AT procurv

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post #24 of 24 Old 05-18-2010, 05:15 AM
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Quote:
Originally Posted by Elill View Post


Edit: just got an AUD price for SMX screen - Stuff Me! A$7500 for 110" 2.35 AT procurv

Get a quote from OzTS for their AT screen. Same fabric (or so I am lead to believe).

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