Intial throw distance calculation 16x9 or 2.35 ? - AVS Forum
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post #1 of 5 Old 02-02-2013, 04:07 PM - Thread Starter
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Sorry guys I searched, I really did, but I am still a little confused. I will be using an "A" lens.

I have found all sorts of calculations [.5625] to get the 16x9 screen size image area inside of the 2.35 screen. I have no issue there. Screen is 117.5 wide, 2.35.1, CIH is 50. 16x9 is 89 wide. All looks good and clear right? Now when I start to calculate the throw distance, is it based on the 16x9 screen width, or the 2.35 screen width?

I think the screen width of the 16x9 is the distance I use to set the projector up. Before I calculate what the "A" lens will do.

Example 89 x 2.2 195.8/12=16.3 feet.


This is where I put the front of the projector lens correct?

Or is it based on the 117.5x 2.0= 235/12=19.58 feet?


If this is the case I have no room to put the projector there. The room is only 21.5 from screen to back wall.



Scenario #1 works perfect.

Scenario #2 Well cut a hole in the wall into the hallway...WAF. Non existent.

Projector will be either Runco LS-5 or Q-650i. Both have no room fro scenario #2 unless I get a short throw lens which will cause pincushion issues, Right?

Anyway thanks for looking.

Dave
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post #2 of 5 Old 02-02-2013, 04:33 PM
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Just to be clear, you are actually trying to work out throw ratio, not throw distance. They are related, but not the same.

We at Panamorph have tried to make this simple by just referring to screen height - that way you don't have to worry about whether or not we are talking 16:9 or 2.35:1 or 2.40:1.

Most Horizontal Expansion lenses like our UH480, DC1, and Cinevista plus lenses from Schneider, Isco and others:


2.85 x the screen height or greater (you can go closer, but pincushion starts to become an issue)

Vertical Compression lenses (like the Whitney, and our U85 and UV200):

4.3X the screen height or greater.

So, for your setup, a Horizontal Expansion lens needs to be 50" x 2.85 or greater back. That math works out to 142.5", or about 12 feet.

For a Vertical Compression lens (like the Whitney), you need to be 50" x 4.3 or greater back. That math works out to 215", or about 18 feet.

Either way, you are ok. If you are going with a Panamorph sourced HE lens (either from Panamorph or one built by us for another company) I would suggest a placement at about 15 feet back for minimal pincushion and the greatest sharpness.

Good luck!

John Schuermann, Filmmaker / Film Composer
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post #3 of 5 Old 02-02-2013, 05:51 PM - Thread Starter
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Thank you John,

That was clear, concise, and very welcome.
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post #4 of 5 Old 02-28-2013, 10:49 AM - Thread Starter
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I don't know if a follow up is warranted or not, but here is what I ended up doing. I took the screen width at 16x9 2.0 distance. The reason for this was the Runco VX-3000i being used has a throw ratio of 1.86/ 2.2. Using just 2.0 gave me a point to set up for that fit all of the calculations as I understood them.

Screen size was slightly changed from the initial thoughts also. The screen is now a Da-Lite Joe Kane Affinity 2.37, 50.5x119.625, custom screen. Stewart was just too much cash. The "A" lens is also now changed to a Panamorph UH-480 with manual sled "B" stock from AVS...What a Deal!!!


The math. 16x9 width =90". 90"x2.0 = 180". 180"/12" 15' Ft. Well guess what? the joists of the ceiling made that impossible, [well really hard] so the mount went where it was easiest 15'9". That make the throw ratio Exactly 2.1. The math 90x2.1= 189. 189/12 = 15.75. .75 of one foot is 9 inches. Nice round figures.

50.5x 3.8= 191.9 . Just slightly over the 189" but most importantly over the 2.85 minimum by almost a whole factor.

No issues without an "A" lens in place.

The UH-480 is in the process of being sent to me.

Wow, nothing I thought I was going to use ended up in the equation. Not the projector, the screen or lens. same outcome different specs.

Why? COST.
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post #5 of 5 Old 03-02-2013, 05:23 PM
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Quote:
Originally Posted by dturco View Post

The math. 16x9 width =90". 90"x2.0 = 180". 180"/12" 15' Ft. Well guess what? the joists of the ceiling made that impossible, [well really hard] so the mount went where it was easiest 15'9". That make the throw ratio Exactly 2.1. The math 90x2.1= 189. 189/12 = 15.75. .75 of one foot is 9 inches. Nice round figures.

The correction lens "A" that comes standard on all the units needs to be at 14.5 ~ 17 feet and so your 15.75 is perfect.

Mark Techer

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