How far from screen for DIYLabs PreBuilt Box?

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#2
macker123 said:
I am thinking about buying the prebuilt box from DIYLabs and then just buy an lcd and lighting somewhere else.

I have 15 feet in my living room to broadcast the picture. How big can I expect the size of my screen to be?
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Hmmm....15 feet length of living room? I tried before using a elmo 4000 lumens OHP, fresnel size 11" by 11". the size was very very big, 10 foot high + by 10 foot long +.
 
#4
With 15" LCD the diagonal size of the projected picture will be about the same as the distance between the projector and the screen. Which is definitely too large in your case (unless your LCD is smaller), that's why we need longer throw, but that would also mean longer focal lengths for the fresnel, projection lens and longer distance between the LCD and projection lens which makes projector too big at least if you use 15" LCD monitor.

Edit: Use this Excel macro to calculate the size ..
 
#5
Under the Fresnel panel text of the calculator is says: Use panel with focal length equal to Lcd to Lens distance or close to for maximum results. The front focal length of diylabs.org special fresnel is 13 inches so I enter that. At a proj lens to screen distance of 150 inches I get a image size of 173 inches. Way to big. What am I doing wrong?
 
#7
Based on the calculator, my Lcd to lens distance needs to be 24inches. This is twice the focal length of the fresnel FL. It is recommended that the Fresnel FL is the same as Lcd to Projection Lens distance. So this means I need a longer FL fresnel which means more light loss in general since I cant use the special brighter fresnel that diylabs has.
If I use the 13 inch FL fresnel but keep my lcd to lens distance at 24 inches what does this mean to my light efficiency even if I use a condenser lens?
 
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