I've got my PJ working finally. No longer have a cooling problem, takes 1 hour to get from 75 degrees F to around 91-92, 2 hours after that the temperature is still in the 91-92 range. Ran my PJ through the Video Essentials DVD for optimizing the picture, picture looks really good now. Tonight I'm going to have my inaugrual first movie viewing which will be geared towards my kids, Pee Wee's Big Adventure.
My problem is that I'm not getting a 1:1 ratio throw distance. My PJ is 8 feet from the screen, and its putting out a 12 foot picture. The PJ eclipses the viewing area from directly in back of it to about 35 degrees on either side. Ceiling mount is not an option, its a 20 foot vaulted ceiling. Positioning it on the floor from that close results in excessive keystoning.
I know the triplet is a fixed focal length and the focus adjustment only has a minimal effect. Is there any adjustment I can make to increase the throw distance? I'd prefer to get it to a 1:1 (12 feet), but I'd be happy with 10 feet.
Thank you all for your previous help.
Full Version: Throw distance question
I really hate the 1:1 generalisation that people use. It's not accurate, and there are other factors as well.
The distance from LCD to field fresnel has an effect on throw. The greater that distance, the shorter the throw. This is because the field fresnel effectively magnifies the LCD, just as a page magnifier does.
The ratio of throw to screen sizes also varies with throw. This is because the distance from the LCD to the lens varies in order to get a focus. It's unpleasant math to determine the true ratio at any given throw, so people just generalise. Then someone comes along wondering why their results are so much different from the "1:1" that they were expecting.
About 1.2:1 of screen size to throw is more in line with what most people are really getting.
Maybe the focal length calculator needs to be re-written... Something that accounts for more real-world situations.
The distance from LCD to field fresnel has an effect on throw. The greater that distance, the shorter the throw. This is because the field fresnel effectively magnifies the LCD, just as a page magnifier does.
The ratio of throw to screen sizes also varies with throw. This is because the distance from the LCD to the lens varies in order to get a focus. It's unpleasant math to determine the true ratio at any given throw, so people just generalise. Then someone comes along wondering why their results are so much different from the "1:1" that they were expecting.
About 1.2:1 of screen size to throw is more in line with what most people are really getting.
Maybe the focal length calculator needs to be re-written... Something that accounts for more real-world situations.
QUOTE
Maybe the focal length calculator needs to be re-written... Something that accounts for more real-world situations.
It's funny that you have mentioned this, I’m doing just that. I’ve tested the formula and they appear to correspond to real life I just have to finish the code.
DJ
mmm, this is the kind of question i like 
.
what is exactly what you did dazzzla?
.what is exactly what you did dazzzla?
I think that 1 other piece of information should be added, which is the distance of the lens from the LCD. Since this seems to affect the throw ratio, I think it needs to be calculated anyway
And one other factor that should be accounted for, is the distance between the LCD and the field fresnel, as the magnification effect of the field fresnel also has an effect.
And one other factor that should be accounted for, is the distance between the LCD and the field fresnel, as the magnification effect of the field fresnel also has an effect.
Yep the LCD to triplet distance is displayed but I’ve chosen not to allow it to be edited. The LCD to fresnel distance will also be included plus the triplet tilt will be calculated.
DJ
DJ
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