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Discussion Starter #1
On the LT150's throw distance sheet, it states the "Throw Ratio" as 1.64 - 1.63:1, "dependent on screen size and focus setting". It later gives a more exact equation for determing the throw distance. Specifically, it's: 1.6288 x Width - 0.5157, which pretty much looks like the previously stated "Throw Ratio".


Is "Throw Ratio" a relatively universal term that other projector manufacturers use? If so, is it always a number that is to be multiplied with the image width, or do some manufacturers intend it to be used with height or diagonal measurements? Is there an easy way to obtain the throw ratio/distance information for most/all projectors out there or would this require getting it from the instruction manuals?


Scott
 

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The Throw ratio will vary from projector to projector to projector.


There is no "universal formula".


Some projector manufacturers have a throw distance calculator -- where you input screen height, width or diagonal, as well as the screen aspect ratio and it will tell you the appropriate distance.


Sorry, this isn't clean and simple, because it's a function of the optics assembly.


Regards,
 

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John, I think you may have misunderstood my question. I realize that the numbers involved will be different from one projector to another. What I'm wondering is if the term "Throw Ratio" is an industry standard term in which this "throw ratio" number, when multiplied by the image width, would provide the necessary throw distance. This is how NEC seems to use this term, but I wasn't sure if any other manufacturers used it.


I believe the answer to this may be "no". While NEC's literature references this "Throw Ratio", Sharp, for instance, does not. In fact, looking at the instruction manual for the Sharp XV-Z7000U, I see that the calculations that they provide for determining throw distance use the image's diagonal size for the calculations. I'm guessing, therefore, that Projector Central's throw distance calculator is the result of their manual effort at converting all of the various manufacturer's calculations into a common formula, as I have suggested (though they may not be using width).


Scott
 

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I have seen two variations, which are reciprocals. The two terms that are used are "throw ratio" and "projection ratio". Most frequently, I have seen "throw ratio" to mean

distance to screen / screen diagonal

and "projection ratio" to mean

screen diagonal / distance to screen


The "screen diagonal" may sometimes be replaced by screen width. The distance to screen is generally measured parallel to the floor (as contrasted to to the center of the screen, which would be different for off-axis projectors).


It is best to look at the diagrams of any manufacturer to see what they intend.


You can also compute these from examples given. For a fixed-length lens, just use the distance and the screen size into the above formulas. For zoom lenses, you have a range to contend with, and you need to compute two ratios, one for each of the extremes of the focal length range. This is often the best way to proceed, since manufacturers tend to give clear examples (e.g, "fills a 10ft diagonal screen at 13.6 ft distance" or some such).
 

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Discussion Starter #5
Quote:
Originally posted by rlsmith
You can also compute these from examples given. For a fixed-length lens, just use the distance and the screen size into the above formulas. For zoom lenses, you have a range to contend with, and you need to compute two ratios, one for each of the extremes of the focal length range. This is often the best way to proceed, since manufacturers tend to give clear examples (e.g, "fills a 10ft diagonal screen at 13.6 ft distance" or some such).
This is what I have been doing. Doing it for multiple projectors can get tedious.


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The most common discription of throw ratio is:


projector's distance to screen / screen width.


which will come up with ratios like 1.8:1 or 1.5:1.


Diagonal will be used on occasion but it is usually width.


-Mr. Wigggles
 
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