What I find hard to decipher is how to figure out what size image I can get at what distance. For example, determining if a particular unit will be suitable for6' wide screen at 14' or10' wide at 30'I know I need 3000 to 4000 lumens for my applications.
I, however, have learned something I didn't expect. I didn't think a 4,000 lumen projector was capable of an image that size under full ambient lighting. I'm starting to wonder just how badly my current projector sucks.
In your case, I'd say 35ft.-40ft. would be the max I'd want to throw for a 4000 lumen projector - and I'd aim for a 9ft. x 16ft. screen if possible
or a 9ft. x 12ft. screen if you need to stick with 4:3 AR. If you have total control of the ambient lighting, those limits may be exceeded by a good bit, but you will always have the most brightness when the projector is as close to the surface as the lens will allow.
...potential variations in what terms such as "full ambient light" and "house lights at 100%" actually represent as far as the light levels on the screen.
Just so others don't get confused, it is the image size rather then the throw distance that directly affects the image brghtness. Theoretically, a projector producing a certain size image will produce the same image brightness regardless of how far it is located from that image as it is still providing the same total brightness over the same image area.
I think that most people would agree that getting the projector as close as possible to the screen surface is best practice. Even if using a zoom lens, there is still noticeable dropoff in the image brightness when compared to a screen that has a projector mounted closer to it...isn't that why a projector with a higher lumen rating would be desired for a greater throw distance?
The simple concept is that image brightness is a factor of having a certain number of lumens from the projector spread over a certain image area and if the projector brightness and image area remain constant then then the throw distance is not a factor. Throw distance can become a factor if it changing causes the image area or projector output to change. So say you had a 4,000 lumen projector creating a 9' wide by 12' high image, that's 4,000/(9x12) or just over 37 ftL (footLamberts). It doesn't matter where the projector is, if the image size and projector brightness remain the same you get the same result. The other factor in image brightness is screen gain or how the screen affects the light hitting it. However, you do not really have to consider that in assessing the image contrast as screen gain tends to affect both the projector output and ambient light about the same. What can happen in some cases is that a different lens or different point in the zoom range may resulting in a reduction in the projector output. Obviously most projector manufacturers are going to rate their products based on the most favorable condition and it is possible that a long throw lens or a lens zoomed in tight may actually reduce the projector output.
What about screen selection? I know the screen has an effect upon brightness, but are some screen types better than others in high ambient lighting? Is it just a matter of highest gain (since a given % loss has a much higher impact on the brighter projection source than the dimmer ambient light)?
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