Curved vs Flat 2.35 Screen

This has come up a couple of times lately: A curved screen is only needed if you have an A Lens in place and even then only if the throw is short which might cause pincushion that the curved screen will compensate for. If you don't intend to use a lens then there is no need to buy a curved screen as it will then cause other problems such that the middle of the picture will go off the top and bottom of the curved screen since the image is projected 'flat' without the lens.

There are only a few reasons to use a curved screen. Some think there are only one, there is a second very important one however.
1) Most common, to reduce or eliminate the pincushion artifact that comes from using an anamorphic lens. You have to be casreful here as teh opposite issue is that with a curved screen you get barrel distortion if you do not have a lens, or the lens is out of the lightpath.
2) To reduce or control screen uniformity with relatively wide screens that have some directionality (gain), e.g a Stewart ST130 or Firehawk.
3) Because you like to look of it. Not really a technical reason but I guess it is a reason.

Using a lens is better than zooming, IMO. But it comes at a price.

When sizing curved screens I recommend consulting with someone that knows what they are doing with Anamorphic and curves. Wendell, email me at scott at techht.com and I can help you.

Best,
Scott

I haven't seen focus be an issue. Remember most people using curved screens and anamorphic lenses move the lens out of the light path when not viewing 2.35. SO they end up with curve and no lens.

If you want it because you like the look of it, the only thing to remember it you will have barrel distortion. If you have a long throw it won't be bad but you will get it. If the PJ is ceiling mounted near the top of the screen, the bottom of the image will curve (smiley face) a little due to the curve intercepting the light beam "early" on the sides.

OK, let me know if I can help. In any case, in your situation, barring any preferences otherwise, I'd recommend a flat screen.

Scott (or anyone), what would deter your from putting in a curved screen? Cost aside, I think the biggest issue I've heard is that it affects contrast (since the screen can reflect onto itself), but how significant is that?

Essentially I've got a 110" wide, well actually I think it's more like 105" by the time you take the moulding into account, screen that I built the frame for and put SMX material (from that first run way back) on. I've been looking at what I can do in to "improve" my theater and a curved screen would eliminate the pincushion (does it reduce geometric distortion too?), but it would look pretty awesome too. That and I could get one slightly larger than what I have now. Just debating my next moves...

SMX says it's not a factor on their curved screen material (cross reflections causing loss or CR). If the screen has any directionality then I'd agree. If not, then I'm not sure. It would be very difficult to measure.

I only prescribe a curved screen for short throws with A-lenses or gain screens generally speaking. If you have a long throw (high TR), and a near unity gain screen, then I'd stay flat. Not sure how getting a curve will allow you to go bigger. It shouldn't.

Sorry, the curve wouldn't allow me to go bigger, I just have a bit of room left in general so I could go bigger, and if I get a new screen, question becomes, do I curve it, for the pincushion correction and cool-factor, or just stick with flat, looks like curved isn't "that" much more expensive (at least not with a Seymour AV which is likely what I'd go with).

Curved would definitely help with geometry/PC, but a torus would be needed for corner to corner perfection. I seriously considering going curved myself.

Careful. I don't remember for sure but I don't think they will let you prescribe the curve radius. I'm almost positive you can't with SE, not sure if Chris will do Seymour to a specific radius or not. And too much curve (too short of a radius) will make things worse, not better. Contact me off-line if you decide to get one and I'll help with screen and curve specs.

Sorry I hadn't gotten back to your PM, but I plugged my numbers into Bob's curve spreadsheet and came up with like 39' 3" radius or something, which is awfully close to the 40' radius Seymour sells. I'd obviously have to double check my measurements first anyway. That and I've got some other projects to finish first so it's sort of all wishful thinking at this point anyway.

Yep, 100% agree on 3) Scott
There is something about knowing when using an a-lens and your set-up (short throw) ditctates the best visual presentation to you/guests, you did the needed items to make that happen.
Plus, it is a converation item when new people come over.



I'd add item 4) improve light control with curved screen (less light spillage onto side walls)

How does having a A-lens compare to having the Video Processor scaling to 2.35:1?

A video processor doesn't scale to 2.35:1. It does the vertical stretch which is needed if using a lens (though it can be done in the projector in many cases also). A video processor can be used the 'shrink' 16:9 content to fit on a 2.35:1 screen once you've zoomed to fill the screen*. This means that 16:9 is displayed at reduced resolution (1400 x 800 approx) so you don't need to adjust the projector's zoom, but it is a compromise.

Using a lens to view 2.35:1 content and then moving the lens out of the way for 16:9 means you can use all the 1920 x 1080 pixels for both aspect ratios (this means that 2.35:1 content is scaled so it does depend on how well the scaling is done for best results as well as how good the lens is).

*In this case the projector is zoomed so that 2.35:1 content fills the 2.35:1 screen (1920 x 800 pixels approx) then the different aspect ratios are achieved by scaling within this (reduced) resolution, so at no time are all 1920 x 1080 pixels used.

Apart from looking very cool, IMHO, I would add that the decreased light reflections from the side walls actually contributes to a better contrast image.

If you can have a room with a permanently installed projector screen, then surely you can decorate the side walls a dark colour (and ceiling since the curved screen makes no difference to the reflection on this surface). It never ceases to amaze me the number of 'dedicated' rooms I see photos of that look lighter than some living rooms, as if decor is above the function of the room. I refer to these rooms as 'not-very-dedicated rooms'

Also, IMHO it isn't very cool if the image bulges over the middle top and bottom of the screen either, since a non lensed image will not line up with the screen (unless you want to go down the route of using artefact inducing/resolution losing JVC pincushion electronic scaling).

Before anyone runs away with this being an idea solution since it's in a Lumagen and therefore must be good you should realise how this works to fill a scope screen:

1. Zoom the image so that a 2.35:1 image fills the 2.35 screen and the 200 or so rows of pixels are projected off the top and bottom of the screen (the black bars).

2. Change the output resolution of the Lumagen such that for 16:9 viewing this content is shown within the now zoomed screen height, therefore 16:9 is now shown at approx 1400 x 800 resolution. In other words it is a rectangle surrounded on 4 sides with black borders, the top and bottom pair being projected off the top and bottom of the screen as per 1 above.

3. Use the NLS setting so that the 16:9 content is now electronically stretched from 1400 x 800 so that the 2.35:1 screen is now filled. You now have an image that is stretched at the sides (like when a TV stretches 4:3 to fill a 16:9 screen) but importantly, you have also reduced the resolution as well, so are viewing 16:9 content shrunk and stretched to 2.35:1 at 1920 x 800 pixels.

However, if you have a Lumagen you have another option (apart from just watching it in 16:9 with side masks which suits me fine ):

1. As per 1 above.

2. Set up a memory in the Lumagen so that the masking is adjusted so that the top and bottom of the image is cropped off to fit the 2.35:1 screen. You then at least see what is left of the cropped image at 1:1 pixel mapping, so less artefacts than the process described above. Of course parts of the image will be cut off and it might mean people's heads and subtitles being cut off. This is a similar effect as watching a 16:9 film using an A Lens and vertical stretch (except the vertical stretch involves scaling).

Note that neither of these solutions will help those wanting to use a curved screen without an A Lens, just those who insist on viewing everything at 2.35:1 on their 2.35:1 screens. Personally, I found that the recent addition of some simple black velvet side masks means that I no longer feel the need to fill my 2.35:1 screen for everything, despite having a Lumagen.

Unfortunately, some people have significant others that don't approve of said darkening of walls.

It's been stated in this thread and many others that a curved screen is only recommended if you have an A-lens, which I do. Otherwise, yes, you will get barrel distortion. I love the scope setup, so getting an A-lens is a no-brainer for me (again, for reasons stated in other threads). The next logical step for me since I have a short throw is a curved screen. I love it so much, that I would tell people to get an A-lens just for the simple fact that it's "needed" in order to have a curved screen.

Oh I'm sure, but it seems such a shame if it's a 'dedicated' room, so it's not like it's the main living room. Always seems a missed opportunity to me (and if I get a dedicate room in the future it will be dark walled and ceiling for sure, otherwise I might as well carry on with my living room set up).

However, the OP was talking about a curved screen and then whether a lens is needed, so IMHVO putting the cart before the horse since a curved screen is a solution to a problem, not a solution that causes a problem.

I was lucky enough that when I suggested I would be a)drywalling over the windows, and b)painting the room black/charcoal, my wife didn't raise any complaints - she understands how 'into' this room I am. It's usually friends or family "you're going to paint the room black????" and give me the look. I'm sure you all know the look I'm talking about;

I've seen that before when I set up my temporary black cloth 'tent' over my screen area, but since the image looks so much better that way I can live with 'the look'.

funny thing is that, since I built my curved screen a couple months ago, I haven't used my A-lens with it cause I have to cut into the wall and build a sled to use it right with the speaker enclosures et al that I built. The A-lens definately improves the picture, I've just been too lazy to do the build.

I don't notice any parts of the screen being out of focus. I don't notice any barrel distortion either. My frame is covered with velvet, but I don't even run the 16:9 image onto it. The image comes about an inch shy of the borders. It probably helps that I am using a new to me projector with way better contrast than my old one. Maybe once the newness of the projector wears off I will start looking for new ways to improve the picture.

As an aside, I watched the Matrix trilogy this weekend and enjoyed it so much cause the picture quality was soooo much better with the new JVC. It was almost like seeing the movie for the first time.

When members are saying short throw... what is considered a short throw?

Generally less that 1.5X the 16:9 image width.

Thanks John,

So 12'5" throw on a 103" 2.35:1 screen with the CineVista should be good to go?

Yes