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Author Topic: So where can I get ...  (Read 3331 times)
Drewid
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« on: December 11, 2015, 12:02:52 PM »

I need a polarising filter that can change direction on a simple switch.
Where can I get a smallish LCD panel without the polarising film? Preferable something where the whole panel will switch on and off on a single line without having to drive an lvds board?
At a push we could use a cheap laptop to run the dewice, so could drive it as if it's an external screen at a push, I'd kinda like to avoid that though.

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Aerendraca
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« Reply #1 on: December 11, 2015, 12:41:24 PM »

How big does it need to be? Are you using the panel to just switch the transparency on and off? What's the plan for it if you don't mind me asking?
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Drewid
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« Reply #2 on: December 11, 2015, 02:52:16 PM »

It needs to be big enough to fit in front of a camera lens so 100 - 150mm square would more than cover it.
I could do with being able to switch the polariser through 90 degrees without touching the camera.

Here's the thing, if you have a polarised light source and a filter over the lens you can get a true shot of the albedo colour of a surface, rotate 90 degrees and you can get the specular reflectance values.  If you do it with four cunningly positioned lights you can also (with a bit of processing) get a surface height description or normal map. This gives you everything you need to create a physically accurate material in-game (which is the big thing at the moment).  I've seen ghetto versions using the lenses from 3d glasses, one over the flash and one over the lens, but i have a hankering for something more accurate than physically rotating a filter.

There's some examples here:
http://filmicgames.com/archives/233

It's an extension of this sort of thing:
https://www.youtube.com/watch?v=_wIgmEch1P8
« Last Edit: December 11, 2015, 05:07:13 PM by Drewid » Logged

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Aerendraca
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« Reply #3 on: December 12, 2015, 02:46:48 PM »

Ok so the best way I can think to do this is to use 2x 5"plus i2c or spi screens of fairly low resolution and use an arduino with the u8glib library to flip the pixels on and off on both screens. If you remove the backlight on both and overlay one on the other (probably at 90degrees to each other) you should be able to flip the polarization at your will.

This is all hypothetical, but this is what i would try. You can pick up small tft screens and arduinos for next to nothing from china and the code is super trivial. I have 2 crappy tft screens, I might even give it a go to test the theory.
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XDjackieXD
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« Reply #4 on: December 12, 2015, 03:06:10 PM »

Ok so the best way I can think to do this is to use 2x 5"plus i2c or spi screens of fairly low resolution and use an arduino with the u8glib library to flip the pixels on and off on both screens. If you remove the backlight on both and overlay one on the other (probably at 90degrees to each other) you should be able to flip the polarization at your will.

This is all hypothetical, but this is what i would try. You can pick up small tft screens and arduinos for next to nothing from china and the code is super trivial. I have 2 crappy tft screens, I might even give it a go to test the theory.
I think this won't really work as the pixels usually have a small space between them.
You could use the LCDs from an 3D-shutter glass (It is pretty easy to remove the filters from these so you have the raw 1-pixel LCD screen to change the polarization).
Another method would be to rotate the filter using a motor.
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Aerendraca
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« Reply #5 on: December 12, 2015, 04:17:08 PM »

Actually im not sure the space between the pixels will have much of an affect since the focal point will be far beyond the tft panel, I imagine the worst case to be that you will lose some light but probably not too much.

3d shutter glass will work too and probably better, but its more expensive than my supremo cheap offering. Smiley

By the way I don't claim that the tft idea will work but it'd be fun to try.
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Drewid
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« Reply #6 on: December 13, 2015, 03:04:31 PM »

Having done some googling LCD shutters are available in welding masks.
http://www.ebay.co.uk/itm/Auto-Solar-Darkening-LCD-Welding-glasses-Welding-Mask-Welding-Goggles-Helmet/291552735881?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D33984%26meid%3Dfa31af4575a54303a065885f35c989bf%26pid%3D100005%26rk%3D3%26rkt%3D6%26sd%3D271361197325
But I guess that's a different thing they're doing.

 Aerendraca - I don't get why it would need two screens? Surely the crystal either gives the light a twist or not?
I'm having trouble visualising it.

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Aerendraca
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« Reply #7 on: December 13, 2015, 05:39:06 PM »

I think you would need 2 screens to overcome the affect of the polarizing material on the glass of the tft. Because with one tft you have a fixed polarizer and one which can flip 90degrees you only have 2 states, ON - where the polarized light makes it through both lcd and glass, and OFF - where the light gets blocked by the glass due to the orientation of the liquid crystals. So that you observe two states of polarization, say 0degrees and 90degrees, you could use the same properties of a 2nd screen to alter the polarization of the OFF state of the first screen.

If you could remove the polarizing film on the tft glass you would only need one screen, but I don't think you will find a screen where this is possible so 2 screens is the next best I can think of.
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Drewid
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« Reply #8 on: December 13, 2015, 05:45:27 PM »

https://www.youtube.com/watch?v=a4cnrPMo6_s
 Grin

Dammit I've also just found out you can get conductive coated glass on ebay. and recent experience tells me it's not that hard to split a screen and get the liquid out.
The glass is expensive though, (£35 for a 100mm square piece) but I'd love to do it just to try it out.


Also as an aside I've finally got myself a 20" screen cheap, It's an apple screen so used the TMDS signal format and not LVDS. At first I though it was a completely different thing so I'd have to hunt for a board to support it, turns out it's basically DVI with different pin arrangement so just a cable will do it, If I also replace the CCFLs with LEDs then that's even easier and there's less interference producers in the box.  I can even power it from an external 12/5v supply Smiley  

« Last Edit: December 13, 2015, 08:51:32 PM by Drewid » Logged

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Aerendraca
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« Reply #9 on: December 13, 2015, 07:59:54 PM »

Nice video, I dare you to give it a go! Wink

I actually have tried this some time back when I had the idea of replacing the ccfl backlight with uv leds. I wanted to use the screen to expose photoresist for making my own pcbs, I wanted to remove the film on the screen to let more light through, seems like a silly idea now though.
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Drewid
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« Reply #10 on: December 13, 2015, 09:37:15 PM »

If my thinking is right you'd only need to get one polariser off.
You'd present the polarised side to the lens, If you take a shot with the screen off then your get 0 degrees, with the screen on then it gives the light a twist on the way through and you get the 90 degrees.

I was thinking of getting some cracked lenses to strip the polariser off to put over the lights,  it is do-able with a blunt knife, but you can get raw polariser from china or the States for about the same as a broken panel and it's not wrecked.

I may be stripping a couple of laptops before I bin them at some point so I might try it on one of those to see how it works.

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Aerendraca
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« Reply #11 on: December 14, 2015, 07:46:08 AM »

I can see where you're coming from but I'm still not sure that this will work. With the polarizer facing the light source you still have the same problem, in that the polarized light source (which is an important point) wont make it through the first polarizer to be twisted by at least one of the liquid crystal states.

I don't know if it will or wont work im just speculating, and I sort of hope you prove me wrong because there would be lots of things you could do with this setup if it works.
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Drewid
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« Reply #12 on: December 14, 2015, 09:51:07 AM »

I meant the other way round, the polariser is on the camera side. So the front gathers the polarised spec + unpolarised diff and delivers it to the polariser on the back. 
So whether the spec gets through depends on the twist state.

We tried using a monitor as a polarised light source just to get a proof of concept for the whole thing. It worked (of course) but wasn't very bright, so we'll need some bright lights and some polar film.
I've found a place in the states that's the cheapest source I can find without buying bulk quantities, though there were a few places on alibaba/ali express that did a 10 pack of ipad sized sheets for a few dollars a sheet.

There was also a vendor selling 300m rolls of the stuff but that's probably 299.5 m too much and besides it weighed something like 400kg so shipping and handling would be a problem. Wink,
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Drewid
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« Reply #13 on: December 14, 2015, 02:10:25 PM »

Nice video, I dare you to give it a go! Wink

I actually have tried this some time back when I had the idea of replacing the ccfl backlight with uv leds. I wanted to use the screen to expose photoresist for making my own pcbs, I wanted to remove the film on the screen to let more light through, seems like a silly idea now though.

So you expose the PBC using an image on the screen?
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Aerendraca
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« Reply #14 on: December 14, 2015, 02:32:23 PM »

Ahh the penny has dropped, i understand what you're trying to do now. I was imagining you requiring two states of polarization, but you only need one because you actually need to remove the polarized light in order to see the specular light.

Exposing pcbs direct from the screen was the idea. If it worked I would have been able to print pcbs with a very tight pitch, trouble was that the leds were peak 400nm so only just in the uv, and glass is good at absorbing uv, so the part of the spectrum I was after was dim to start with and dimmed further by the glass. I'm tempted to revisit the idea at some point with a bit more careful thought. It almost worked by the way, it took about 20mins to partially expose a small area of photoresist but the backlight didn't quite have the umph to do the job properly.
« Last Edit: December 14, 2015, 02:41:14 PM by Aerendraca » Logged
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