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Discussion Starter #1
As a result of my preparations for conducting some screen captures, I took some time to 'think' about how the projector-screen-viewer function occurs. Because I'm using a CRT, it was natural that the installation presented a nice frame of reference in the form of a free body diagram.


My projector projects at a 11? angle of declination onto the center of the screen. The viewer (me) is looking at the center of the screen from a 11? angle of inclination. Angle of incidence equals angle of reflectance.


When looking at some screen manufacturers' websites, the 'viewing cone' is often expressed as a function of viewing angle vs. screen gain. Almost everyone takes into account of this function in better understanding the seating consequences as it relates to brightness, but this is only a horizontal consideration.


What I have not heard anyone talk about was the screen-gain as a function of angle of inclination. Since I do not know what means of setup a digital projector has--I assume it varies from one digital projector model to the next--I, for my endeavor, only focused on CRT. Thus, I wonder if one realizes that at a >10? of inclination the screen's gain has changed.


With this in mind I took the liberty of looking at the Stewart Studiotek130 screen as its a relatively popular screen for CRT use. When looking at the chart for the screen-gain as a function viewing angle, it appears that the gain is around 1.0 (for a screen rated at 1.30). Unfortunately, I do not know if this gain chart (and others by Draper, Da-Lite, etc.) can be used for vertical angles of inclination by the viewer.


So, now I wonder if many are taking this into consideration when trying to match up a screen-gain to the angle in which they are viewing the screen. I also tried to look at a Stewart product for a negative gain (Grayhawk), but the chart's representation on my monitor was so small that I couldn't read the values on the X-Y axis to make sure I was reporting a relatively accurate interpretation for >10? angle of inclination.


Do many consumers not consider this aspect of screens? How about businesses that are selling the equipment? Installers?
 

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I know I didn't when I purchased a Cinemavision 1.3 ISF screen. Because my projector is mounted mid screen, all of the benefits of an angular reflective low gain screen were gone. I had more hot-spotting and color shift than on the retro reflective High Power, exactly because of the angle of incidence. I would think that on digital, the different offsets that are prevalent would have a great impact on the performance of a given screen.
 

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I also wonder how all this plays into screens with compound curves, both true torii and pseudo torii.
 

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Quote:
Originally posted by WanMan
I also wonder how all this plays into screens with compound curves, both true torii and pseudo torii.
Not sure but I think most with a torus screen angle it up a little bit to compensate.
 

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Discussion Starter #5
To compensate for what, gain fall-off? I guess this would be the case since in using a torus or compound curved screen you are essentially creating one giant hot spot if angling the screen up isn't conducted there would be a perceived or observed brightness-uniformity drift at the center-bottom of the screen.
 

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I dont know exactly what you are asking but the light dispersion is uniformly round "viewing cone". So same effects up down as side by side.


There is only one product I have come across that has a wider viewing cone horizontally than vertically. Its the Vutec Silverstar.

http://www.avsforum.com/avs-vb/showt...96#post2263996
 

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Discussion Starter #8
I suppose I wasn't asking anything, Tryg, but making an observation. The observation in and of itself is meaningless unless the angle becomes significant, which I noted in setting up a CRT projector. As a result, the gain was reduced due to setting up the projector according to its design. Thus, even though I bought & mounted a screen with a 1.3 gain, I cannot be getting this amount of gain at my seating position, which is vertically perpendicular, but 11º below the horizontal.


I did not know if the cone was radial, a different function for the X vs. Y-axis, etc.
 
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