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#### Tin_Can

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I need some help understanding throw ratio. The distance from the projector to the screen is 22'. The screen is 10' wide and 2.35 ratio. If I'm only using a lumagen for anamorphic, no lens, what is my throw ratio?

I thought it was 22/10=2.2, but I was told it was actually 2.91. 2.91 makes sense if using a lens, I think, but just using a lumagen is 2.2, right?

#### GetGray

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##### Scott Horton, techht.com
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Here is the formula I use and recommend. There is no ambiguity when using it and you can't the the TR wrong if you use it:

TR= [distance from PJ lens to screen in inches] / [ viewable HEIGHT of screen] * 0.5625

Example:

54" tall screen, 13' from PJ lens to screen

Distance to screen is 13' * 12 = 156"

TR = 156/54*0.5625
TR = 1.6

#### Tin_Can

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##### Registered
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Discussion Starter
Here is the formula I use and recommend. There is no ambiguity when using it and you can't the the TR wrong if you use it:

TR= [distance from PJ lens to screen in inches] / [ viewable HEIGHT of screen] * 0.5625

Example:

54" tall screen, 13' from PJ lens to screen

Distance to screen is 13' * 12 = 156"

TR = 156/54*0.5625
TR = 1.6
Thanks. Is that for use with an anamorphic lens? What if you're just zooming in and using a lumagen to switch aspect ratios?

#### GetGray

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##### Scott Horton, techht.com
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5,743 Posts
The forumla is aspect neutral. If you are zooming, you use the virtual screen height. That is, the height of the projected 16:9 rectangle.

If you are doing the worst of the worst, using a Lumagen to get 2.35:1 (because you are both scaled and zoomed or both at all times), then you use the height of the 16:9 projected beam. Which will be taller than your screen.

The PJ doesn't know how big your screen is. The TR applies to your PJ's optics. To get the TR, you use that formula and the height of the image the PJ is producing, whether you are "using" all of that projected image on the screen you put in front of it or not.

#### Tin_Can

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##### Registered
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504 Posts
Discussion Starter
The forumla is aspect neutral. If you are zooming, you use the virtual screen height. That is, the height of the projected 16:9 rectangle.

If you are doing the worst of the worst, using a Lumagen to get 2.35:1 (because you are both scaled and zoomed or both at all times), then you use the height of the 16:9 projected beam. Which will be taller than your screen.

The PJ doesn't know how big your screen is. The TR applies to your PJ's optics. To get the TR, you use that formula and the height of the image the PJ is producing, whether you are "using" all of that projected image on the screen you put in front of it or not.
Thank you, that clears it up for me!

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