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Join Date: Feb 2001
Location: Silicon Valley, CA
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Okay, thanks. Here's how to figure this stuff out.
A 92" diagonal, 16:9 screen is 80.18" wide. Let's call it 80" to simplify a little.
The "throw" of the projector is usually expressed as a range of two numbers. For example, it might be something like 1.39 - 2.11. You multiply those numbers by the screen width you want to achieve, and that tells you the minimum and maximum distance from the screen that the projector can be and still project that size of picture.
As it happens, 1.39 - 2.11 is the throw range of this projector, based on JVC's chart. (I figured this out by referring to their 120" column and working the throw calculation backwards -- it's not given explicitly.)
So, for your 80" wide screen, we multiply 80 by 1.39 to get 111.2. Multiplying 80 by 2.11 gives 168.8. So, you can put the projector 111.2" - 168.8" from your screen (roughly 9.25' to 14').
At the short end of the range, due to the optics in the zoom lens, you typically will get the brightest image, but perhaps a little less contrast. At the long end of the range, you will get less brightness, but perhaps a bit more contrast. Most people try to hit the middle of that range if they have the flexibility, because it gives a nice compromise between contrast and brightness.
What about that cryptic formula you referred to?
L(minimum) = 31.1781 (1 7/32) x SS - 46.1543 (1 13/16)
L(maximum) = 47.0644 (1 27/32) x SS - 42.3308 (1 21/32)
Ow, my head. That confusing jumble is because they're trying to accommodate both metric and Imperial units. The decimal numbers are millimeters, and the numbers in parentheses are inches. (It took me ten minutes of staring at this to figure that out, by the way.) "SS" is the "screen size", but in this case, it's the diagonal dimension of the screen. Note that there are two charts in the book, one for 16:9 and one for 4:3.
The millimeter numbers in the book are given to much higher precision than for inches -- it looks like they actually generated the true numbers using metric values, then converted to the nearest 1/32 of an inch. Why don't we use the high-precision metric numbers, but convert them to decimal inches for our convenience?
31.1781mm = 1.2275"
46.1542mm = 1.8171"
47.0644mm = 1.8529"
42.3308mm = 1.6666"
Now, our formula is a bit clearer:
L(minimum) = 1.2275 x SS - 1.8171
L(maximum) = 1.8529 x SS - 1.6666
Plugging in your 92" diagonal screen, we get:
L(minimum) = 1.2275 x 92 - 1.8171
L(maximum) = 1.8529 x 92 - 1.6666
L(minimum) = 111.1129"
L(maximum) = 168.80"
How about that? Pretty darned close to the numbers we got above using just the throw figures derived from the chart!
I think the formula is more precise than using simple throw figures, since there is a small correction factor (the subtracted number), but using the throw numbers should get you pretty darned close for typical theater screen sizes.
Mike Kobb(Formerly "ReplayMike". These opinions are mine alone, and in no way reflect the opinions of employers past or present!)"Mike's Money Pit" Build Thread