[Jeff Smith]

After noting so many different opinions on thr "rainbow" effect of DLP, I figured the problems of hot spotting with high gain screens must be similarly also variably annoying.


Can anyone put there observations into objective terms? Ie. how many degrees off axis does it actually bother you. Do you have to be within the screen width to have a good picture?


I guess I want someone to say how far you have to move your haed back and forth to notice it, if it is notable looking from one side of the screen to the other, and if the increased brightness makes up for it if you are NOT sitting in the sweet spot.


For the sake of discussion lets say a gain of around 2 with a fairly big 8-10' wide screen.


------------------

Jeff

Currently - Zenith 7" CRT, 80x60 1.3 gain screen


Soon to be - 107x60 1.3 gain...with ?Seleco 250 with Panamorph or "cheap" 9" CRT

 

[KFung]

If you want to see a TORUS screen head out to an AMC theatre with HITS (High Impact Theatre System, I think). Those screen are all TORUS designs.


Results depend on the brand of high gain surface (they all have different fall-off characteristics), the throw distance of the projector, and the uniformity of the projector (CRT's often have light fall-off in the corners that can be aggravated by high gain screens). It really depends.


In any case, I don't believe trading a hotspot for more brightness is really a good idea, uniform brightness over the screen is highly desireable.


Regards,


Kam Fung

 

[Jeff Smith]

I agree and understand the hot spot concerns, but I just dont know how to judge how much trade off there is at 1.3, 1.5, 2.0 etc...without actually seeing it. Small swatches dont give you an acurate idea, it would be nice if you could rent a 6' piece to demo...it'd be worth the money before dropping $1-2000 on the final product.


Its too bad our hobby has so many LARGE EXPENSIVE NON-MOVABLE variables. It would be nice to simply whip out a G90 at a store and fire it up, fully converged, with 3 or 4 processors on 3-4 different screens...then do the same with a 9500LC and 3 chip DLP and Martinized DILA...I quess thats where Alan and the forum come in. One day I'll fly up there if he ever gets his G90.


------------------

Jeff

Currently - Zenith 7" CRT, 80x60 1.3 gain screen


Soon to be - 107x60 1.3 gain...with ?Seleco 250 with Panamorph or "cheap" 9" CRT

 

[KBK]

And when he gets the G90, I will take my HTPC there, and put it up against all comers. Then we will see if I know S**t from shinola.


------------------

goosystems.com


Ken Hotte

[email protected]


[This message has been edited by KBK (edited 06-27-2001).]

 

[deronmoped]

I have a 161" 16x9 curved silver painted screen with a gain of 2.5, I'm using a Sony 1272. It's in a 16' wide room. I can walk from wall to wall and not detect any hot spotting. The curve of the screen removes any noticeable hot spotting and how often do you have a movie that would show this, the point is you are not watching a test pattern which the hotspotting might be noticeable in. If you want high gain with no hot spotting try a curved screen.


Deron


------------------

Surfs Up!

 

[Jeff Smith]

Deron,


What did you use for your material and/or frame? I'm looking to DIY.


------------------

Jeff

Currently - Zenith 7" CRT, 80x60 1.3 gain screen


Soon to be - 107x60 1.3 gain...with ?Seleco 250 with Panamorph or "cheap" 9" CRT

 

[deronmoped]

I built a curved frame out of plywood and 2x3's and attached 4x12' sheets of drywall to the frame and finished the seam with drywall tape and drywall mud. Its all most like building a wall in a house. You could actullay hire a carpenter and a drywaller and they should be able to do it for you. Then prime and paint it.


Deron


------------------

Surfs Up!

 

[Laurence]

Quote:

Originally posted by deronmoped: I have a 161" 16x9 curved silver painted screen with a gain of 2.5, I'm using a Sony 1272. It's in a 16' wide room. I can walk from wall to wall and not detect any hot spotting. The curve of the screen removes any noticeable hot spotting and how often do you have a movie that would show this, the point is you are not watching a test pattern which the hotspotting might be noticeable in. If you want high gain with no hot spotting try a curved screen. Deron

You must get some pretty noticeable color shift with that much gain and that size spread.

 

[Mike2]

Jeff.


Have you seen this site? They address hotspotting, gain, etc. and curved screens.
http://www.kodak.com/US/en/motion/ne...7/screen.shtml


Mike

 

[Laurence]

Are these Vutec curved screens "Torus"?
http://www.vutec.com/ultrahighgain.html

http://www.vutec.com/catalogjpg/12.jpg




[This message has been edited by Laurence (edited 06-29-2001).]

 

[CINERAMAX]

Hello Laurence,


The VUTEC is a randomly curved screen, it's radiusses are definetly NOT like a TORUS. Which I had the privilege of experimenting with on two jobs.


I will add more anecdotal and tecnical TORUS stories to these threads soon, I am a bit overworked now.


Regards

 

[deronmoped]

Laurence, I know if I wanted to I could fine all kinds of problems with a large high gain screen. What I think makes it work is I always watch movies on the screen and I hardly ever encounter any scenes that would show the defects and not having a side by side comparison of a correct screen I don't have anything to judge it by. What was more important to me was having the impact of a large image.


Deron


------------------

Surfs Up!

 

[KFung]

Laurence,


No, the Vutec is not a TORUS screen, although it does use the same principles. I think the Vutec is a section of a sphere, where the TORUS is, naturally, a section of a torus. The equal curvature in the horizontal and vertical direction on the Vutec is decidedly not optimal, OTOH it's a presenation product and the viewing conditions are much different.


Regards,


Kam Fung

 

[KBK]

The answer to that one.. is they don't use perforated screens. The sound will not work properly in such an enviroment at all. The pressure losses would be ridiulously high. It would never stay in one shape.


So, they are not perforated. This leads to a problem with reflective noise... cummulative problems abound. I had a solve for that, once... it's a long story.


Imagine a form, that's edges are exactly forming the exact edges of the lines that would describe the outside edges of a torus, or toroidal section. ie, the outside edges of the screen that is a torus. Now, imagine a box that has this shape for an outer edging. Now, drape your screen material over that 'form' boxe's opening. tie it down tight, so it is air tight, but stil hanging loose.... the right amount of loosness. Now, vaccuum pump out the inner space of the box. The 'skin' of a screen tightens over the box form/edge,and curves inward as much as the vaccuum will allow. The combination of the natural curve described by the vaccuum, and the box form edges stressing the screen material wil describe EXACTLY the right curve. Getting the loosness of the material just right over the exact right box edge curve and shape...dictated by the viewing area, all these things exactly right is the real trick.


Corners are a real ***** to get right.


------------------

goosystems.com


Ken Hotte

[email protected]

 

[Jeff Smith]

I still have the bug to learn more about how the shape is determined and kept accurate. I look forward to any insight Peter. It seems hard to believe such an accurate shape could be held in so many complex directions using a vacuum pump.


By the way, if comercial theaters use this method, how do they keep the suction through the perforated screens they all use?


------------------

Jeff

Currently - Zenith 7" CRT, 80x60 1.3 gain screen


Soon to be - 107x60 1.3 gain...with ?Seleco 250 with Panamorph or "cheap" 9" CRT

 

[CINERAMAX]

J Said


"I agree and understand the hot spot concerns, but I just dont know how to judge how much trade off there is at 1.3, 1.5, 2.0 etc...without actually seeing it."


On My Two Torus the lesson is simple: 4 gain screen noticeable color shift GIANT TRINITRON LOOK,On a custom sprayed white 2.7, no colr shift, film look.



Both with New projectors BV1200HD back in 1993,two 11 foot wide TORUS SCreens, one ATLAS was designed for 1 row only with the 4 front row for show.


The other PHOEBE designed for a 5,4,3 row where the front 3's edges were ignored RAY TRACING wise.


Best seats, back row atlas, standing behind second row phoebe-The wider one. We are talking fraction of a degreee or a degree and a fraction of toroidal angle differential between the two here. About 15-16 TD


For the record, the DEEPER TORUS screen had slightly more focussing and geometry issues, althouh it is perhaps the more 3-d, at least from it's No compromise single viewing row.


These are general observations regarding the best seating position for a Torus, Ironically, my findings say nothing against small viewing area ray tracing, in fact, narowcasted 3-d imagery of the Torusses and other solid compound curved screens, (Circus Circus Theme Park Two Imax rides) provides dramatic depth effects.



Why the 2.7 screen

In response to Joel Silver's Color shift issue,(I told Don S to make me a high Gain Wfite. He custom sprayed it for a simulation batch of TORUS and PHOEBE.

 

[REW]

TORUS screen at least doubles the gain.(Kodak site).

Thus 4gain silver screens(like Stewart 400)Dalite has one too turn into 8+gain screens(no hotspot).So 40-80FL is easy and affordable for 1PJ and double that for 2.

Suddenly CRT delivers best pic and brightest too!DIY makes it inexpensive as the compound curving is reduced to a typical family of curves for the most likely home setups.

Ok Kam Fung-let it rip!
http://www.avsforum.com/ubb/smile.gif http://www.avsforum.com/ubb/smile.gif


------------------

Ron

"Your priorities will be different-its the weighting that counts!"

 

[Iceman]

Torus screens do nothing to improve gain. The gain comes from the screen material and is independent of screen shape. What the torus shape does is to make the brightness even across the entire screen. Some people refer to this as widening the hotspot.


However, if you project a white image on a torus screen with a particular high gain material, the brightness will be higher than for a flat screen of the same material. This is due to the focusing effect of the torus but cannot be interpreted as increasing gain.

 

[Mike2]

"Torus screens do nothing to improve gain."


That depends on how you define gain. If you choose to define gain with respect to the angle of the viewer (as the Sigma Designs authors do), then compound curved screens do indeed increase gain. Others define gain as a characteristic of the screen surface alone. Then the screen shape is always irrelevant and your statement is correct.



"However, if you project a white image on a torus screen with a particular high gain material, the brightness will be higher than for a flat screen of the same material"


Again, it depends on how you define brightness. There are those that would say the brightness must be identical because brightness is measured in ft lamberts and the calculated ft lamberts for 2 screens of equal area and equal gain are identical - regardless of shape.


The authors of the Kodak article have chosen a different "directional" definition of ft lamberts with respect to the viewing position. By that definition, ft lamberts are higher, the Torus is brighter, and you are correct again.



It can be very confusing when there is not a generally agreed upon definition of terms.

 

[CINERAMAX]

"A curved screen will not give you more gain (gain as a property of the screen), the brightness at the centre of the screen will be the same as a flat screen."


It is time to requantify brightness as a VALUE of even Illumination reaching a viewing area.