To curve or not - Page 5 - AVS | Home Theater Discussions And Reviews
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2.35:1 Constant Image Height Chat > To curve or not
stevodude's Avatar stevodude 10:53 PM 01-28-2007
I would say that calculating the curve with combination of Lense & no lense would be halfway inbetween...

ie completly flat surface is perfect for a projector without anamorphic lense, and based on what your projector image curve actually makes with the lense system as the maximum curve. ( can be calculated, but I measured with the 'stick method' )
so for me:

projector: panasonic ae700
lense: DIY anamorphic set for 2.35:!
screen: DIY curved PVC/foam gain of around 1.2

initially I put the lense up and setup as correctly as I could, and gave me an equal curve horizontally top and bottom.
Used a long pole that reached vertically from the ground to above the top of the projected image and marked the top and bottom of the image on the stick at the center (horizontaly) of the image. I then moved the stick to the Left hand edge of the image and moved the stick towards the projector until the marks lined up with the image. Then I measured the distance to the wall, this gave me the "rise".
from that you can calculate the radius ( for me it was around 9.4 meters I think) , but doesn't matter as I can calculate the circle from the width of image I want and the 100mm rise from the L & R edges.

you can calculate the radius from the Width of screen and rise with:

screen curvature radius = r
Screen width = w
screen rise = sr

r=( (w/2)^2 + sr^2) / (2 * sr )

And with that formula you can calculate any point on the curve.
see this post for the worksheet that Mark.J.Foster kindly worked out.

for me thats in cm:

R = ((274/2)^2 + 10^2) / (2 * 10 )
R = ((18436 + 100) / (20 )
R = 926.8cm

So if you want optimal for both, then that iwll be half of the curve, so make it 50mm rise on each side of the screen, to get an average of the 2.

but for me I'm going to leave lense in place and compress the image for 16:9, as you allways have to have some loss somewhere at difference aspects, but minimal because I'll be mostly viewing dvd's, and sometimes Hidef dvb sports channel occasionally.

So really you need to look at your usage...

>%50 in 1.76 format then keep it flat and remove lense when not needed, and have a good masking when you do
50/50 1.76/2.35 then maybe half the rise for your curved screen and good masking
>%50 in 2.35 format then use mostly lense and 2.35 full rise for your curve, and remove lense with good masking, or use the compress image to 4:3 for less quality 1.76 format (loose %30 horizontal pixels)

Thats my take on that.
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pyro2003's Avatar pyro2003 07:29 PM 09-19-2009

Going 2.35 using a SIM2 HT300Plus, sitting at about 11' , do I really need a curved screen (Stewart, Firehawk, acoustic transparent) ? The hoizontal is 81" only

The other advantage I see is the room is not completely black (white ceiling and walls) so maybe the curved screen can help ?

wtongco's Avatar wtongco 03:53 AM 09-22-2009
Newbie trying to clarify some information.

Considering JVC RS25, 95 to 108" Wide CineW 1.3, prismasonic HD5000R, low ambient light

1. I understand the curved screen is supposed to increase the viewing cone. Am I correct in thinking that viewing will still be good if my outer seats are outside the width of the screen, or do I need to place my seats within the width of the screen?

2. I have some additional width and was going to place my R/L speakers to the side of the screen. Considering what I am reading, am I crazy for not maximizing my screen and going acoustically perforated. I am very interested in a high quality picture that will view well when there is low ambient light and audio quality for music listening.
pyro2003's Avatar pyro2003 09:40 PM 09-28-2009
was told if the throw ration is closer than 1.6 (divide lens to screen by screen width desired), then the anamorphic lens will need to correct for pin-cushioning effect. So for my case for if doing 2.35 (which I have decided not to), the throw is 1.39 so i need it
CAVX's Avatar CAVX 02:26 AM 09-29-2009
Originally Posted by krholmberg View Post

Anybody... Please!

I know a lot you have curved screens... please tell us about your screen, especially what works and doesn't work!

The exact curve is TR and A-Lens dependant. The name I know this as is called 'ray tracing' and whilst it sounds complex, it is not rocket science and you can do this yourself. The easiest way to do this is to use a stick on a stand that is tall than your screen.

Vern describes the process earlier, here is my version.

1. If the screen is mounted to the wall, then place the stick in the centre of the screen as close to the surface of the screen as possible whilst projecting through the lens onto the screen.
2. Mark the image height on the stick- IE the top and bottom of the beam from the projected image.
3. Move the stick to one end of the screen and you will notice that the beam now extends beyond the original height.
4. Move the stick out from the wall to the point where the beam is now the same size as the orignal markings.
5. Measure this distance back to the wall. This is now a representation of how far the ends of the screen need to come out. Both ends should be the same if the lens is set up correctly.

If you can make your screen to curve to match the measurments you've taken, your image will be perfectly framed and you will have elimated pincushion caused the anamorphic lens.

My screen was orignally flat, and I have curved it using a custom rig. You can read about it HERE.
Vern Dias's Avatar Vern Dias 02:33 PM 09-29-2009
That's the way I did it. The result will be a perfect curve for your installation to compensate for pincushion.

CAVX's Avatar CAVX 06:52 PM 09-29-2009
Originally Posted by Vern Dias View Post

That's the way I did it. The result will be a perfect curve for your installation to compensate for pincushion.


My screen is thread adjustable meaning I can customize both the top and bottom (if need be) to perfectly match. May I ask what you used for framing to hold your screen in shape?
Vern Dias's Avatar Vern Dias 01:44 PM 09-30-2009
1x2's. Simple, light, and cheap.

Customizable corners wouldn't work for me because the masking and curtain tracks have a fixed curve.

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