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ways to reduce pincushion

post #1 of 26
12/22/12 at 8:58am
Thread Starter 
I have a pretty drastic pincushion with the bottom of my screen but not the top using a Panamorph 480.

My throw is 17'6".

I notice in a lot of pictures that the lens is tilted down a lot. Way more tilted than mine. Is this the best way to reduce pincushion? Physically I would have to raise my projector a few inches to do this but I want to keep lens shift to a minimum.

I may do this if that is what is required, but I don't want to if that isn't the main cause for the pincushion.

I have the light beam entering the center of the back of the lens and exiting the center of the front of the lens.

thanks

ed
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post #2 of 26
12/22/12 at 9:01am
Thread Starter 
I am going to build a curved screen this weekend but the pincushion looks to be about 2" at the bottom. I do not know if this will compensate for that much or not. I thought pincushion at this distance wasn't supposed to be this dras
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post #3 of 26
12/22/12 at 9:01am
Thread Starter 
I am going to build a curved screen this weekend but the pincushion looks to be about 2" at the bottom. I do not know if this will compensate for that much or not. I thought pincushion at this distance wasn't supposed to be this drasti
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post #4 of 26
12/22/12 at 9:34am
I have adjusted my lens tilt so that the pincushion is averaged between top and bottom of the screen: If tilt it in one direction I can have straight lines at either extreme such as the top, but the pincushion is double on the opposite side such as the bottom. With tilt set correctly, then the centre of the screen has no pincushion and it gradually increases towards the top and bottom (not that much in my 2.7 throw set up, but still evened out.

I might be worth you trying to adjust the tilt to see if you can even out the pincushion then it might not be so much of an issue (though curved screens do look cool anyway cool.gif).
Edited by Kelvin1965S - 12/22/12 at 9:42am
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post #5 of 26
12/22/12 at 1:24pm
Thread Starter 
sounds like I need to raise the pj then and tilt the lens down to try to even out the pincushion top and bottom. thanks mate.
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post #6 of 26
12/22/12 at 1:56pm
You need to get the 16:9 image lined up and in focus without the lens, first. Then add the lens and adjust the tilt, roll, focus and angle of the lens to the optimum position. You shouldn't need to adjust the image height using the lens really: With my Isco II the image is lined up first then the lens just expands (and slightly by 5% or so increases the height), but it expands equally on both sides and by the same small amount top and bottom.
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post #7 of 26
12/22/12 at 2:12pm
Thread Starter 
the 16:9 image is good. My problem is that I cannot tilt the lens down since I am projecting thru a wall (unless I raise up the pj on the other side of the wall)
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post #8 of 26
12/23/12 at 12:24am
if you can't tilt the lens without raisng the projector, are you able to drop the lens?

Tilting will allow you to even out the pincushion top to bottom.

A curved screen is the only way to eliminate it, however, if you watch a lot of 16:9 program and move the lens to do so, I would stay with the flat screen.
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post #9 of 26
12/23/12 at 2:15pm
Thread Starter 
building my curved screen tonight biggrin.gif
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post #10 of 26
12/23/12 at 7:26pm
But, unless I'm mistaken, if you can't tilt the lens to even out the pincushion, even with the curved screen you'll still have pincushion, or at least some sort of distortion.
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post #11 of 26
12/23/12 at 10:16pm
Thread Starter 
ok. the curved screen was a kind of aside. Still going to do it cause I think it looks cool. Top and bottom are cut but project had to be put on hold to watch a movie with the wife and her friend.

I have always heard that you want the lens as close to the pj lens as possible so I did not try tilting the lens down due to architectural restrictions. I pulled the lens out in front of the wall and tilted it down and got a uniform picture. So... I am going to tear into the wall so that I can tilt the lens down and still have it right next to the pj lens. I think I will build a pocket so I can just drop the lens into the pocket at the same place every time for scope content and then pull it out for 16:9 content.

I tried zooming again one more time to see if I could just live without the hassle of the lens. I did after all just get a JVC 4810 with the e shift 4k wobulation. Believe me, the added resolution/brightness of the lens still adds a lot to the picture, even with the supposed 4k image of the JVC.

I am wondering how much of an improvement I am going to realize getting the tilt on the lens right? I guess we always are looking for that little something extra.
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post #12 of 26
12/25/12 at 7:47am
What is the size of your screen?
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post #13 of 26
12/25/12 at 9:08am
Thread Starter 
i just built a curved frame that is 126 wide with a 40' radius.

the old screen was 123 wide i used to watch it masked down to 117 " so the screen is going to be anywhere from 117 to 126 (with a little experimentation)
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post #14 of 26
12/25/12 at 9:59pm
Thread Starter 
kind of leaning toward 117. Liking the sharper, punchier image thing over the immersive experience thing. (also would not have to buy more screen material)
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post #15 of 26
12/26/12 at 4:18pm
Quote:
Originally Posted by edfowler View Post

ok. the curved screen was a kind of aside. Still going to do it cause I think it looks cool. Top and bottom are cut but project had to be put on hold to watch a movie with the wife and her friend.
I have always heard that you want the lens as close to the pj lens as possible so I did not try tilting the lens down due to architectural restrictions. I pulled the lens out in front of the wall and tilted it down and got a uniform picture. So... I am going to tear into the wall so that I can tilt the lens down and still have it right next to the pj lens. I think I will build a pocket so I can just drop the lens into the pocket at the same place every time for scope content and then pull it out for 16:9 content.
I tried zooming again one more time to see if I could just live without the hassle of the lens. I did after all just get a JVC 4810 with the e shift 4k wobulation. Believe me, the added resolution/brightness of the lens still adds a lot to the picture, even with the supposed 4k image of the JVC.
I am wondering how much of an improvement I am going to realize getting the tilt on the lens right? I guess we always are looking for that little something extra.

As you have discovered, the solution here is simple. You just need to tilt the lens to follow the light beam from the projector. It's simply a matter of tilting the lens until the pincushion is even top and bottom.

There are no other real advantages to tilting the lens other than to get the distortion to even out.
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post #16 of 26
12/26/12 at 4:47pm
Thread Starter 
hey John,
really really like your 480. I have tried a couple other lesser lenses before and did not care for them. Looks like the 480 is a keeper.

I'm building a curved screen tonight. after it is done I'll start a build thread in the diy 2.35 section
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post #17 of 26
12/26/12 at 5:05pm
Cool! Thanks for the comments smile.gif
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post #18 of 26
3/16/13 at 6:24pm
Not sure if anyone can help me with this? I thought this might be the first thread to try with regards to picture distortion, and a non-anamorphic pincushion effect is my issue. I am getting a very slight pincushion effect in both 16:9 and zoomed 2.35 aspect ratios on an Elite fixed frame 235 screen. I know this is nothing to do with the issue of anamorphic lenses, but using the test pattern during set-up I am finding it very difficult to get the bottom white line to sit perfecting on or slightly above the masking; there is a slight 2 or 3 pixel droop on both left and right sides of the image (but not on the top). I know the screen is not distorted in any way - it is vertical and tensioned flat - so I suspect it must be related to the way the PJ is sitting on its shelf perhaps? I am new to the projector game, so any suggestions would be gratefully received.
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post #19 of 26
3/17/13 at 5:30am
Quote:
Originally Posted by stanger89 View Post

But, unless I'm mistaken, if you can't tilt the lens to even out the pincushion, even with the curved screen you'll still have pincushion, or at least some sort of distortion.

In his opening post, he describes his image as has a flat top edge and a curved bottom edge. If he projects onto a curved screen, the top edge will now barrel whilst correcting the bottom, so the image won't be perfect. He needs to get the pincushion even first, then correct that with the curved screen.
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post #20 of 26
3/19/13 at 9:33am
Quote:
Originally Posted by musicalfox View Post

Not sure if anyone can help me with this? I thought this might be the first thread to try with regards to picture distortion, and a non-anamorphic pincushion effect is my issue. I am getting a very slight pincushion effect in both 16:9 and zoomed 2.35 aspect ratios on an Elite fixed frame 235 screen. I know this is nothing to do with the issue of anamorphic lenses, but using the test pattern during set-up I am finding it very difficult to get the bottom white line to sit perfecting on or slightly above the masking; there is a slight 2 or 3 pixel droop on both left and right sides of the image (but not on the top). I know the screen is not distorted in any way - it is vertical and tensioned flat - so I suspect it must be related to the way the PJ is sitting on its shelf perhaps? I am new to the projector game, so any suggestions would be gratefully received.

It would help to know which projector you are using, screen size and throw distance. It could be that you are tilting the projector in some way, or that it is not square with the screen. There is also the fact that some projector lenses have some built in pincushion or barrel distortion (the old Screenplay 7200 had quite a bit of barrel distortion in its optics).

Good luck!
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post #21 of 26
3/19/13 at 1:25pm
If your projector has a pincushion correction, don't use it, they add artefacts!
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post #22 of 26
3/19/13 at 9:14pm
Quote:
Originally Posted by John Schuermann View Post

It would help to know which projector you are using, screen size and throw distance. It could be that you are tilting the projector in some way, or that it is not square with the screen. There is also the fact that some projector lenses have some built in pincushion or barrel distortion (the old Screenplay 7200 had quite a bit of barrel distortion in its optics).

Good luck!

Thanks, John. My projector is the Epson 6010 with a 9ft throw and a 77.5 x 33in screen. The projector is located on the opposite wall below the plain of the top masking, so I am using a small amount of downwards lens shift. (I use zoom to achieve all different aspect ratios including 2.2, 2.35 and 2.40:1 to maintain a constant height, but the slight pincushion is visible to me on all ratios.) None of my movie audiences notice this and of course it is neatly hidden with masking, but the only annoyance is to the perfectionist me!
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post #23 of 26
3/20/13 at 12:20pm
Quote:
Originally Posted by musicalfox View Post

Thanks, John. My projector is the Epson 6010 with a 9ft throw and a 77.5 x 33in screen. The projector is located on the opposite wall below the plain of the top masking, so I am using a small amount of downwards lens shift. (I use zoom to achieve all different aspect ratios including 2.2, 2.35 and 2.40:1 to maintain a constant height, but the slight pincushion is visible to me on all ratios.) None of my movie audiences notice this and of course it is neatly hidden with masking, but the only annoyance is to the perfectionist me!

I don't see anything here that should influence pincushion. It is possible that your particular projector has a defective lens, or that the 6010 has this particular issue. Any way you can get your hands on another 6010 or even a different projector altogether for comparison?
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post #24 of 26
3/20/13 at 12:41pm
Quote:
Originally Posted by John Schuermann View Post

I don't see anything here that should influence pincushion. It is possible that your particular projector has a defective lens, or that the 6010 has this particular issue. Any way you can get your hands on another 6010 or even a different projector altogether for comparison?

I don't think it's a defective lens because I didn't have the problem before taking the projector off its shelf to run some cable tests. I suspect I may have to do a little more tweaking. And you may be right about the lens not being absolutely square on. Either way, it's not a complete deal breaker, as it doesn't even register with subtitles (but does slightly with Blu-ray bottom-screen progress bars). I will keep working on it and thanks again for your help.
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post #25 of 26
3/20/13 at 1:32pm
I agree that making sure the lens is square to the screen is your best course of action. Let us know how things turn out.
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post #26 of 26
3/29/13 at 9:42am
Still haven't been able to resolve the effect. It's very weird because, like I said, the slight left and right 'moustache' wasn't there before removing the projector from the shelf and all hardware is in the same place. I'm thinking of getting a calibrator guy over who can run some patterns and maybe help me diagnose.
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