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Discussion Starter #1
Let's say I get a JVC G-15 and I want to use it with a 96" x 54" screen mounted at a throw distance of 18 feet, and the projector is going to be ceiling mounted. Let's assume the screen top is 82" high. My understanding (based on a previous post by Tom Stites) is that I would have to mount the projector at 91" high to have the 16:9 panel appear on the screen correctly. (Nine inches of the 4:3 panel of the projector would appear above the screen and 9" would appear below it, as the 4:3 panel for a 96" inch wide screen would be 72" x 96"). Does that seem right?


Ok, so now I add the Panamorph, which I understand will cause the image to be shifted downward if the projector is not tilted. Ok, so how much will the image drop? I keep hearing different figures to use (.048 or .075 multipled by the throw distance). Also, I assume this means that if I don't move the screen, that I have to raise the projector a certain amount of inches to get the image centered on the screen (again assuming no tilt)? The keystoning only results if you tilt the projector to avoid changing the height at which it is mounted, right?


What would be the difference in this configuration between the original Panamorph and the OEM mentioned in another thread. I have to admit I don't get it.

 

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Smitty,


To make it easier, assume that your image will normally be at or near the top of your screen. Top of screen will be at or near middle of Gxx lens. On 16:9 material, this is done by using Horizontal Position on the Gxx.


With no tilt, the ratios are pretty basic.


With the Original P751 lens, 18' x 12" = 216 x .048 = a 10.3" image drop.


With no tilt using the OEM P752 lens, 18' x 12" = 216" x .08 = a 17.2" image drop.


Width will supposedly stay the same with both lenses.


If you plan on the 2.35 lens, the image drop with no tilt will be very close to that of the OEM lens.


Chris

 

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Smitty,


Your calculation for PJ height without Panamorph is right.


The different figures for the image drop depends on which

of the two versions of Panamorph you get. The original

design, Model P751; drops the image by 0.048 inches drop

per inches of throw. The new design, Model P752; drops

the image 0.075 inches drop per inch of throw. [ As an

aside, the new 2.35 AR Panamorph will drop the image by

0.08 inches drop per inches throw - close to the P752.]


Yes, if you add a Panamorph, and don't lower the screen,

you have to raise the projector, assuming zero tilt.

If you tilt the projector to compensate for the drop, then

you have some degree of keystone, which can be corrected

by tilting the screen - the Cygnus calculator tells you

how much.


With regard to the setup, the difference between the

two Panamorphs, the P751, and P752; are the differences

in the drop rates - 0.048 [P751] vs 0.075 [P752].


Greg
 

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I think the thing that is hard for everyone, is what will happen if they get the 2:35

Panny or they go into bypass mode for 1:33.


No doubt a .075 drop has its benefits but this will also present some problems.


If you try to use bypass mode the 1:33 image will jump up very high (off your

screen) so effectively the bypass mode will become difficult to use for a lot of

people.

The only real option is to leave the lens in place and scale to suit (loosing some

resolution and brightness)

But some may not have a scaler that can do custom scaling and so this could be a

catch as well.


Now in this example I will use my favorite no tilt, no keystone scenario. If you are

planning on using both a 1:78 and a 2:35 panny the 2:35 image will end up being

very close to the same height (top) as a 1:78 image so the skinny 2:35 image will

jump to the top of the 1:78 screen and change the center line. Now you can use

tilt to get your centerlines right but you introduce keystone and depending on

projector and masking this could be a problem.

Sure I know the 3% keystone is not noticeable but I seem to notice it and any spill

very easy and it annoys me.

Anyhow just some thoughts.

Do the DILAs have digital keystone correction ?



DavidW


[This message has been edited by David Wallis (edited 06-20-2001).]
 

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Discussion Starter #5
Ok, now you done gone and got me confused again. How will the Panny work with external scalers? For example, assume I have a JVC G-15 and I'm using a Quadscan Elite, which I understand allows me to place the 16:9 panel at the top of the G-15's 4:3 panel (which will also allow me to align the lens of the G-15 at the same height as the top of my screen). Thus, the excess of the 4:3 panel is at the bottom only. To watch 4:3, the scaler puts the 4:3 panel in the middle of my 16:9 screen.


Ok, now we add the Panny. When I want to use the Panny, I use the full 4:3 panel right? Should I assume that the Quadscan Elite and other scalers can do this? It seems like they would be able to, but I don't know. If so, I now add the Panamorph and it squeezes the image back to 16:9 right? But where will the image be? Since I have the projector set up to use the top of the 4:3 panel normally, won't the image now be too low? So doesn't that mean if I plan to use the Panny, I should not use the scaler's ability to put the 16:9 panel at the top of the screen, but I should let it be at the middle of the screen?


Also, if I raised my projector so that the 16:9 image when used with the Panny is right on the screen, what happens when you remove the Panny? Won't the usual 4:3 panel be higher now, i.e., most of the excess of the 4:3 panel will be on the top of the screen? So how is my scaler going to give me a 4:3 panel in the middle of my 16:9 screen panel? Won't that panel be higher now?


I must admit that once again I am totally confused. I concede this may be due to my own ignorance, but I have to confess it does not seem intuitive at all how this thing is going to work if it shifts the image downward when you use it for 16:9, but not for 4:3 when it is slid out of the way. It would seem the only ideal option if you want to watch both 16:9 and 4:3 is to tilt.
 

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Smitty,


The setting for putting the 16:9 image at the top of the screen is related to not having an anamorphic lens, and usually using a 4:3 screen.


There is nothing to worry about.


With a Quadscan or HTPC and the 16:9 panamorph with the D-ILA it will be setup in 4:3 1365 X 1024 mode, which is what gains you the extra brightness of using all of the panels pixels for 16:9 media.


It will have the same drop as outlined above, and the 2.35:1 lens will also use the 4:3 1365 X 1024 setting, and have roughly the same picture height as the 752 lens.


-Dean.
 

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Where is this .075 coming from?


Quote from Shawn:

"The natural down-shift that this OEM design yields is approximately 0.08 times the throw distance (a 12†drop for each 12.5’ throw). Interestingly, this offset would be similar to that of the 2.35:1"


The original is .048, the oem is .080, the 2.35 is .081, right?


Quote for a 4:3 solution:

"The only real option is to leave the lens in place and scale to suit (loosing some resolution and brightness)"


That definitely makes the most sense. Otherwise you'll actually have to have the top of screen at the height of the Pj lens and mask down from the top when watching anything other than 4:3.


If you were building or buying a custom screen, that could work without any scaling. A 96" x 54" screen would have to be plus x inches taller, the x being whatever your image drop ends up being for your throw distance. Of course, then you'd have to zoom to get the image in the screen height, but we do that now anyway, don't we?


Chris

 

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Chris,


The drop ratio of 0.075 for the P752 was specified by

Shawn Kelly in:
http://www.avsforum.com/ubb/Forum10/HTML/006794.html


Quote from Shawn:


"Manny, good question! The new version actually

has an image drop of 0.075 x throw without

tilting the projector."


In the quote you cited Shawn said "approximately"

whereas in the above he said "actually". Shawn

gave us a value with 2 significant digits instead

of the single significant digit of his previous post.


Greg
 

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Discussion Starter #9
Dean, when you say there is nothing to worry about, I want to believe. I truly do. But I still don't understand how the Panamorph is going to work with 4:3 material when you slide it out of the way if the use of the lens causes the image to drop. Won't you have to adjust something (i.e., the projector height, the tilt, or the screen) to get the image to be in the right spot when you go back to 4:3 (assuming you have made the adjustment so that the 16:9 image is centered perfectly in your 16:9 screen)? Sorry if I'm being thick.
 

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Thanks Greg, I didn't remember reading that.
 

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Discussion Starter #11
I went back to the Panamorph web site, and read more about how the lens work. I think I understand now that the top of the 16:9 image resulting from the Panamorph will be x inches below the top of the 4:3 native image. I had not understood that before. I thought the 16:9 image produced by the Panny would be x inches below the 16:9 image produced by the projector. Duh!


It also appears, though, that the degree to which the 16:9 image is below the 4:3 native image is based on the throw distance. Thus, it would appear to me that it would be a matter of luck if your throw distance is such that the 16:9 image is centered on the screen when using the Panamorph AND the 4:3 image when the Panamorph is slid away is still centered in the screen, assuming no projector tilt. Wouldn't this only result when the amount that the 4:3 image is above and below your 16:9 screen is equal to the throw distance multiplied by .048? Thus, it seems in many cases, there would have to be some slight adjustment of the projector when you want to go back to 4:3. Or does the tilt enable one to configure both the 16:9 image from the Panny and the 4:3 non-Panny image such that they are both centered on the screen?
 

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You will have no problem in centralizing the image on both the Original and the OEM, but this will involve some keystone issues depending on your throw distance.

(more throw = more down = more tilt to correct).


Remember this only applies if you want to use the Panamorph in By-Pass mode for full 1:33 resolution and brightness. By scaling 1:33 you will only use only part of your panel but the Panamorph remains in place for all ratios, so you will always have a central image and no keystone.


Remember that even a 1:78 native panel like the 10Ht will lose resolution and brightness when showing 1:33 images. (its the square peg in a rectangle hole thing again)

If you want to use By-Pass you will incur some keystone issues that may or may not be a problem to you.


DavidW
 
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