XP21N + IMX depixelation lens - The good, the bad, and the ugly - AVS Forum
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post #1 of 12 Old 04-22-2001, 03:44 PM - Thread Starter
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The XP21N came close to meeting a high quality projector for my viewing conditions, but the screen door was still a bit too pronounced for my setup.

Screen size 8' x 4.5'
Screen to audience 14'
Screen to projector 19'
HTPC with ATI Radeon All in Wonder

I tried the Cygnus IMX depixelation lens (about $900) to reduce the pixelation. The design of the IMX is quite clever for those who aren't familiar with it. It does not blur individual pixels or the image. Instead, it uses a pair of lenses to create a ghost of the image that can be shifted diagonally (or otherwise) by a user adjustable amount. The effect is equivalent to having 2 projectors half as bright overlaying their images with an offset that is a fraction of a pixel.

My test procedure was to (1) display an image where screen door was more prominent, (2) view it without the IMX from a distance where the effect was noticeable, then (3) view it again with the IMX at a distance where the picture was equivalent to without the lens.

The Good: Where properly calibrated, the IMX lens does reduce the screen door by 30% or better. In other words, the screen door effect for an image at 18' without the lens will look approximately the same at a distance of 12'.

This is a dramatic improvement in two ways. Obviously, it means I can sit where my normal viewing position is without a screen door effect. Second, it the primary artifact becomes pixelation and scaling due to resolution rather than screen door.

The Bad: Adjusting the IMX lens is tedius, even with a binocular. Not a surprise since I've heard it many times before.

The Ugly: I can't get the IMX to ghost uniformly across the screen. In fact, some areas of the screen are always shifted by more than a pixel regardless of any of the other areas whereas I would need consistent subpixel shift on all areas. This means there's a lot of bluriness for non-uniform areas.

I'm wondering whether this might be due to the shorter throw distance of the projector and the mounting of the XP21N. Perhaps the shorter throw distance and mounting away from the projector lens requires more uniformity across a greater region of the IMX optics than for other projectors.

The way that I test for uniformity is to place some 1 pixel width text on the middle of all 4 sides of the screen (left, right, top, bottom), then try to get the same offset for the ghosted image for all 4 positions. I haven't even tried the more rigorous test of placing the text in the all 4 corners yet.

Unfortunately, I'm fighting time and only have a couple more days to decide. There are two questions I have:

1. If you have an IMX, do you see uniform offsets across the entire screen?

2. I have a 4" dim green blob below the center of the screen. It's quite noticeable during credits, dark scenes, and dark shadows in that area. Does anyone having an XP21N see this?

Regards,
Piney




[This message has been edited by piney (edited 04-23-2001).]
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post #2 of 12 Old 04-22-2001, 04:08 PM
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Post pictures if possible.

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post #3 of 12 Old 04-22-2001, 04:59 PM
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I would try to angle the IMX.

I am assuming that you have the lens on flush. Try pulling one of IMX edges forward very slightly. I believe the gold set screw could also help this, but I am assuming you have set this already.

If all else fails, email shawn at cygnus.

I have heard of slight uniformity problems with the lens but I haven't heard of anyone having a full pixel width of difference.

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post #4 of 12 Old 04-22-2001, 05:14 PM - Thread Starter
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MrWiggles: That's one of the things I tried but the lens is pretty tolerant of angle, making the image consistently inconsistent. I've turned the gold screw and knob so much I'm afraid they're both completely out of tolerance. Nonetheless, nothing I do reduces the offset below 1 pixel on the left side other than rotating the lens to the 45, 135, and -45 degree positions. However, this is already the best of the 4 choices - the others are worse.

Ken: I'll post pictures as soon as it's dark enough. I have no light control to speak of.

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post #5 of 12 Old 04-22-2001, 05:20 PM
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Piney,

I know what you mean. I'm trying to watch Springsteen on HBO-HD right now and I wish I had your XP-21N. One bad thing about daylight savings is the ambient.

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[This message has been edited by kelliot (edited 04-22-2001).]

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post #6 of 12 Old 04-22-2001, 05:28 PM
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I have read many posts complaining about the screendoor on the 21N. I have pretty good vision and a 21N. I would really have to try to let that very little screendoor effect, bother me. I really think one would be better of spending their money somewhere else. I like the simple idea of just tapping the focus a bit as to make the screendoor nearly invisible. The slight softness makes the picture more theatre-like anyway.

My set-up is a 21N at about 11' away onto a Luminous white wall. I sit about 10' away (temporary HT). I had just sold a DLP projector and was frankly worried about the pixelation issue when switching to the LCD. This especially after reading the threads on this subject herein. It turned out to be a non issue (for me).

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post #7 of 12 Old 04-22-2001, 06:01 PM - Thread Starter
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wvrich: If you sit 7-8' away instead of 10', your viewing conditions will be equivalent to mine, assuming you're using the longest throw possible. That extra 20% to 30% makes quite a difference. Also, changing the focus does more than just blur the image - I'll take some pics to show why.

Ken: Watching with ambient light was a big requirement. But the minimum width of 8' and a 4:3 panel negate that advantage to some degree.
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post #8 of 12 Old 04-22-2001, 06:47 PM
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In some ways I agree with wvrich. The motorized focus makes it pretty easy to bring the XP21N a little out of focus. Just stand next to the projector and tweak. The Cygnus should help a little bit. If it doesn't, return it.

The alternatives to the XP21N are few. DLPs and CRTs are pretty dim and DILAs are expensive, louder and noisier. Other LCDs have as much or more screen door and less contrast.

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[This message has been edited by kelliot (edited 04-22-2001).]

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post #9 of 12 Old 04-22-2001, 08:08 PM
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Piney,

I used the Cygnus for quite a while back when I had a Sharp DW100U...in fact I still have the newest version IMX if anyone wants to buy it! http://www.avsforum.com/ubb/smile.gif

Anyway, for what it is worth, I use the Windows desktop when adjusting the IMX by dragging some desktop icons (the fonts are great for focusing) around to the corners and then ensuring the projector is focused without the IMX. Then I try and achieve a good focus with the IMX. Once I have the projector and IMX focused evenly I turn to the de-pixelizing. I turn the screw to the point it begins to blur then back off slightly to retain the sharpness.

I'm not sure if this helps but I thought it would be worth a try. You may want to try and back off the gold screw a bit so that you have something to work with when you go to focus as described above.

Good luck,

Tom



[This message has been edited by tommyboy2 (edited 04-22-2001).]
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post #10 of 12 Old 04-22-2001, 11:28 PM - Thread Starter
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Here are some pictures of text with and without the IMX. The IMX was configured to be as uniform as possible throughout the screen. The left image shows what the text looks like without the IMX. It looks close to this at all positions on the screen.

The overexposed middle image is what text looks like through the IMX on the bottom portion and upper right part of the screen. The last image shows the text on the upper left part of the screen.

http://www.hankenmono.com/zhobbies/s...n/imx-text.gif

If the Cygnus can create a uniform effect across the entire screen, the imrovement would be dramatic. However, the pictures above were taken with the Cygnus configured to be as sharp as possible across the screen.

- Piney
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post #11 of 12 Old 04-23-2001, 12:09 AM
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I sit 12.5 feet from an 80 inch wide screen with my 21N and can occasionally detect the screen door if I have my projector sharply focused; however, it only takes a little bit of defocusing to totally remove the screendoor and I don't detect any noticeable deterioration of the image caused by the defocusing. Given how good it looks I doubt I'll be looking for an IMX. I will be in the market for the panamorph when it is available though...

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post #12 of 12 Old 04-23-2001, 04:05 AM
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Thanks for the pics. I think the two glass lens in the IMX must be out of whack. I'd back off the gold screw a lot and try again. If not, then I'd call Shawn at Cygnus and get that exchanged/fixed. The lens should be much more uniform than the results you are getting IMO given my experience.

Tom
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