It might be help
Hi,
circular rings from fresnel panel will projected to the screen if it's distance to the LCD panel too close so both fresnel rings and LCD panel become as single object for projection lenses, try to move away (1" to 2") from LCD and the rings will disappear or at least unfocus.
see you.
Hi,
circular rings from fresnel panel will projected to the screen if it's distance to the LCD panel too close so both fresnel rings and LCD panel become as single object for projection lenses, try to move away (1" to 2") from LCD and the rings will disappear or at least unfocus.
see you.
Oh, Rings. I suppose that we should get this problem sealed up.
(sorry for the pun, but Skinnyboy started it)
I agree with our friend from Jakarta. The downside of the overhead projector is that they want projected transparency (panel) virtually no the same focal plane as the lens. Putting distance between the two should allow you to get the panel in focus without a sharp fresnel image. With motion picture film you can actually see the focus adjust though the celluloid and onto the emulsion. A similar effect should be possible with the panel.
If the depth of the focus plane is too great you might have trouble finding a sweet spot where one is in focus and the other is not. If this happens a company called Rosco makes a number of diffusion films for film and television lighting. There are about a dozen different color neutral films (they call them gels) to choose from. If shifting the focal plane doesn’t work I can dig out a catalog and try to help figure out which would be best for this application. I think they make a product called “medium frost” that would be about right. There would unfortunately also be a drop in the amount of light transmitted though the system.
(sorry for the pun, but Skinnyboy started it)
I agree with our friend from Jakarta. The downside of the overhead projector is that they want projected transparency (panel) virtually no the same focal plane as the lens. Putting distance between the two should allow you to get the panel in focus without a sharp fresnel image. With motion picture film you can actually see the focus adjust though the celluloid and onto the emulsion. A similar effect should be possible with the panel.
If the depth of the focus plane is too great you might have trouble finding a sweet spot where one is in focus and the other is not. If this happens a company called Rosco makes a number of diffusion films for film and television lighting. There are about a dozen different color neutral films (they call them gels) to choose from. If shifting the focal plane doesn’t work I can dig out a catalog and try to help figure out which would be best for this application. I think they make a product called “medium frost” that would be about right. There would unfortunately also be a drop in the amount of light transmitted though the system.
That sounds great! I was thinking about some kind of filter that blurs the fresnel image but not the LCD. I assume that's what your talking about. Yeah, if you could find a specific filter in that catelog that you think would work I'd be all over it. Thanks a lot, you guys have been a big help.
Roscolux
Roscolux #101: Light Frost
Offers softened beam.
Roscolux #102:
Light Tough Frost Changes ellipsoidal into flood or scoop.
Roscolux #103: Tough Frost
Has twin qualities of wide diffusion and warm center.
http://www.rosco.com/main.html
Here is a site that cells single 20x24" sheet for $5.25 a piece
http://www.stagelighting.com/roscogel.html
From playing around with the swatch book, I think I'd recommend going straight to the 103. Holding a sheet over my laptop display, it does seem to soften the pixel edges with about a 1 stop (half the light) loss in light. The effect is best when not in contact with the display 1/4" is pretty good.
101 has only about a quarter of the light loss, but its a bit grainy and might cause moray with the rings or pixel grid .
But hey, at $5.25 a sheet, you might want to try all three.
I’ve been wondering that if this is really a solution, why the panel manufactures don’t offer it as a cheap option. I understand that for lecture purposes fresnel rings are no big deal. entirely different from cinema.
But then again, if the panel distance can be shifted from the lens, and the focus shifted a bit to cure the problem, I'm sure (almost) that they’d doing it.
Let us know how it works.
-Dave
Roscolux #101: Light Frost
Offers softened beam.
Roscolux #102:
Light Tough Frost Changes ellipsoidal into flood or scoop.
Roscolux #103: Tough Frost
Has twin qualities of wide diffusion and warm center.
http://www.rosco.com/main.html
Here is a site that cells single 20x24" sheet for $5.25 a piece
http://www.stagelighting.com/roscogel.html
From playing around with the swatch book, I think I'd recommend going straight to the 103. Holding a sheet over my laptop display, it does seem to soften the pixel edges with about a 1 stop (half the light) loss in light. The effect is best when not in contact with the display 1/4" is pretty good.
101 has only about a quarter of the light loss, but its a bit grainy and might cause moray with the rings or pixel grid .
But hey, at $5.25 a sheet, you might want to try all three.
I’ve been wondering that if this is really a solution, why the panel manufactures don’t offer it as a cheap option. I understand that for lecture purposes fresnel rings are no big deal. entirely different from cinema.
But then again, if the panel distance can be shifted from the lens, and the focus shifted a bit to cure the problem, I'm sure (almost) that they’d doing it.
Let us know how it works.
-Dave
A Fresnels lines per inch
Here is the skinny on the ring thing. The only real way to get around seeing the rings is using a fresnel with more lines (rings) per inch. Most fresnels have a low ring count per inch and when you start looking into finding a fresnel with a higher ring count per inch, you quickly see the price going up. Raising the lcd panel does help, but most of use want maximum light through the panel and not under and out the sides of it (even if you block the light from escaping, it doesn't mean it is still usuable). I truely believe that more lines per inch is the answer to minimizing the ring issue, but finding an affordable one is another question. There are fresnels of sorts that don't use the lines in a conventional way, but whether or not they would be of use, I don't know.
Here is the skinny on the ring thing. The only real way to get around seeing the rings is using a fresnel with more lines (rings) per inch. Most fresnels have a low ring count per inch and when you start looking into finding a fresnel with a higher ring count per inch, you quickly see the price going up. Raising the lcd panel does help, but most of use want maximum light through the panel and not under and out the sides of it (even if you block the light from escaping, it doesn't mean it is still usuable). I truely believe that more lines per inch is the answer to minimizing the ring issue, but finding an affordable one is another question. There are fresnels of sorts that don't use the lines in a conventional way, but whether or not they would be of use, I don't know.
Well you could build a box to raise your lcd up a little bit, just paint it black then to trap most of the light in it.
I originally had my laptop screen 1/2 inch off of the stage glass and experienced allmost no screen door, I built a box with 2 axial cooling fans (very slick rig...runs for hours and gets barely warm) but now I see screen door where I didn't before. The box raised the LCD to allmost 1.50 inchs off the stage glass (too lazy to reconstruct just now to lower it back down)
The fresnel rings aren't apparent for me...but in your experiments to rid yourselves of yours (by raisng the panel)...have you noticed screen door oddities?
zardoz
The fresnel rings aren't apparent for me...but in your experiments to rid yourselves of yours (by raisng the panel)...have you noticed screen door oddities?
zardoz
Zaordoz, how exactly is the screen door worse? It is possible that the rings were actually disguising the screen door? That's the effect I'm having now. It looks like a bunch of diamond shaped pixels because the fresnel rings are criss-crossing with the pixel boarders. This is actually much more degrading than seing just a clean grid.
I tried lowering my fresnel, and the optics were misaligned, so I have to figure out a way to raise the LCD.
I tried lowering my fresnel, and the optics were misaligned, so I have to figure out a way to raise the LCD.
Lifter
It seems as though each pixel is more "brightly in focus" if that makes sense..the image quallity is the same at the raised height as it was in the "lowered" format. That is to say I can still get good clean sharp image. I have read...(and I really wish I kept better notes so I could point out where) that "the fresnel needs to be as close as possible to the LCD panel for the best image". Come to think of it...my image brightness has suffered a little also, the lowered version was on a junk 360watt ENX ELMO now the raised version is on a much more powerfull 3M9550. I disregarded this when I built the box to hold and cool my panel, didn't figure it would prove to be problem...seems like I was wrong. The only reason I haven't re-built it is because I'm waiting for new pannels to arrive ...so would be facing a re-build anyhow on the better LCD.
zardoz
It seems as though each pixel is more "brightly in focus" if that makes sense..the image quallity is the same at the raised height as it was in the "lowered" format. That is to say I can still get good clean sharp image. I have read...(and I really wish I kept better notes so I could point out where) that "the fresnel needs to be as close as possible to the LCD panel for the best image". Come to think of it...my image brightness has suffered a little also, the lowered version was on a junk 360watt ENX ELMO now the raised version is on a much more powerfull 3M9550. I disregarded this when I built the box to hold and cool my panel, didn't figure it would prove to be problem...seems like I was wrong. The only reason I haven't re-built it is because I'm waiting for new pannels to arrive ...so would be facing a re-build anyhow on the better LCD.
zardoz
Yes I've lost some brightness and now I can clearly see the "line" between pixels, obviously that "line" was there before..it's just more noticeable now. In DVD's it's not too bad at all...watching TV from a sattelite feed the pixels are noticed unless I go to full screen mode, then it is so diminished it doesnt matter. Full screen I'm projecting 10ft by 8ft image. But I don't notice rings at all, regardless of how high or low the LCD is mounted.
zardoz
zardoz
Interesting. It could be that your particular fresnel just doesn't show it as much. Also, I'm assuming your LCD is at least some distance from the fresnel, even when you have it as low as possible. W/ my setup, the LCD is actually mounted in where the stage glass used to be, so it's possible that mine is closer and therfore I get a more noticable ring effect.
That very well may be the differance! I've been thinking about this for a while now as it will affect the eventual design of my custom box. As far as I understand the f/p is something like 14 inchs on my 3M (stage glass to triplet) and by raising or lowering the LCD I am playing with that f/p, possibly outside of it's adjustable tollerance?
zardoz....just won a 9inch wide "enlarger head" (8 inch f/p) so it's ALL gona change soon.
zardoz....just won a 9inch wide "enlarger head" (8 inch f/p) so it's ALL gona change soon.
possible solution to fresnel lines
In other posts Lifter has stated that his screen brightness level is quite good and that he usually runs his OHP on a lower setting.
Try this cheap fix and see if it works.
Cover or replace the clear plastic top of the OHP with a white acrylic plastic. This will probably reduce some light output but it will diffuse a lot of the light and may break up some of the lines.
If the fresnel is not a separate piece than the plastic cover just try adding the plastic on top to see what happens.
Plastic resellers often sell remnents for $ 1.00 a pound.
Hezz
In other posts Lifter has stated that his screen brightness level is quite good and that he usually runs his OHP on a lower setting.
Try this cheap fix and see if it works.
Cover or replace the clear plastic top of the OHP with a white acrylic plastic. This will probably reduce some light output but it will diffuse a lot of the light and may break up some of the lines.
If the fresnel is not a separate piece than the plastic cover just try adding the plastic on top to see what happens.
Plastic resellers often sell remnents for $ 1.00 a pound.
Hezz
I had a slightly differant idea...
I think a quick "mist" of "opaquing spray" for window glass would do a good job (sometimes called window "frosting"). You'd have to take care to make sure your coverage is even, but as far as I recall you can get this stuff in "removable" form as well. I've seen this applied in a very fine mist that barely made a differance to the amount of light transmitted through it.
zardoz
I think a quick "mist" of "opaquing spray" for window glass would do a good job (sometimes called window "frosting"). You'd have to take care to make sure your coverage is even, but as far as I recall you can get this stuff in "removable" form as well. I've seen this applied in a very fine mist that barely made a differance to the amount of light transmitted through it.
zardoz
Hmm, all you get with opaquing the light is a worse focus. Any light difused in this way wont follow the wanted path to the pj lens and is waisted. As I said b4, the rings are interference patterns. Try to find a solution to change the light-bundle-width from the fresnel so it wont be the same or a multiple of the dotpitch of the LCD. (eg. lowering/lifting the lcd, the light-bundle-width changes as it gets closer to the pj lens. Just a tiny change should work)
If you are using a screen with a pattern on it then scrap it! I had terrible interference rings with a silver/glass beat coated screen, and none with plain paper. (Interference with the dotpitch of the lcd & the pattern from the screen)
If you are using a screen with a pattern on it then scrap it! I had terrible interference rings with a silver/glass beat coated screen, and none with plain paper. (Interference with the dotpitch of the lcd & the pattern from the screen)
An old-school member (sorry, forgot who) here posted some links to some difusing filters that only cost $5 each. I emailed them and never heard back. Anyways, I think rapsac is right. I still haven't been able to raise my panel, but I'm pretty confident that it will eliminate the rings when I do.
Changing the height of the LCD would be my first experiment also. We strive to achieve the highest lumen output through our LCD's it just goes against the grain to diminish it ...no matter by how little.
zardoz
zardoz
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