This technique is generally inspired by Tim Roth, but i want to make some changes ("enlighted" acrylic doesn’t looks good for me, because of price and it’s properties).

I have an idea, that frosted acrylic will work the same way. If we’ll use frosted acrylic for FTIR, so all the light will go thru frosted side (remember, FTIR), and the we’ll get the same effect, except no highlight to camera.  Also “frosted film” could help. So, basically we’ll get almost uniform illuminated surface.

It is just an idea, but I’ll test it next 2-3 days, and will keep you updated:

Original DSI Article

How will you get even illumination though? Let us know how the tests go. I’ll add this to the “Multitouch - Getting Start” once we iron this out some. I hope it works =)

it sounds interesting Skeet,
i am about to build one more screen , so i should try this ...

just wondering how this affect the projection ?

Guys, just wait a little, i’ll get new piece of acrylyc on tuesday and will test it

great !

I noticed Tim’s post on Friday and have been thinking about it all weekend while away.

Fingers crossed that this approach works

If not, I wonder what frosting the underside of enlighted would do, as this could solve the issue that a lot of IR is being sent to the camera.
But enlighted does seem to create a even illumination really well.

Frosting the underside does have the downside that the image will be projected against this so there will be a gap in between the image and your finger

Sounds good.

I hope it might work for you, but I tried that with a small piece. It illuminated the whole thing nicely and the camera couldn’t detect a blob, because none were produced.

FTIR
That last letter is key to the function. R=reflection by making one side frosted, the IR light reflections become very perturbed by th euneven surface and scatter all over escaping over the entire surface.

Tinkerman - 15 June 2008 05:43 PM

…
That last letter is key to the function. R=reflection by making one side frosted, the IR light reflections become very perturbed by th euneven surface and scatter all over escaping over the entire surface.

That was exactly what i mean
Whatever, if my theory will not work, i’ll definitely will use original DSI method from Tim.

Well, my camera won’t differentiate between the overall IR glow and a finger reflection.

I used a frosted on one side piece of acrylic. Not the right stuff I see now…

This is from Tom’s link:
This acrylic uses small particles that
are inside the material, acting like thousands of small mirrors. So when you shine IR light into the
edges of this material, the light gets redirected and spread to the surface of the acrylic.

That acrylic mentioned called Endlighten
You can get some here:
http://www.professionalplastics.com/ACRYLITEENDLIGHTEN

Good luck!

Hi guys....

well I think that the endlighten acrylic is not much more expensive than normal acrylic. Its just a bit harder to get.
@skeet What do you mean with “"enlighted" acrylic doesn’t looks good for me, because of price and it’s properties”

I also tested the 3mm thick endlighten and I would say it works as well (concearning the light distribution).
I could think of setup using the 3mm Endlighten and glueing it to a piece of thicker, normal acrylic…
so you would not have to get the expensive, thick endlighten.. It might also solve the problem with material softness..
But I gues you would have to use SMD Leds, when working with material thats 3mm thick…

So Layering would be:

fingers
------------------------
diffusor surface
------------------------
10mm Acylic
------------------------
3mm Endlighten
------------------------

Not sure how the IR Light would react when switching the material… I will test it some time this week…

I have been tryng hard to get my hands on some Endlighten. ANyone know where/ how in the US?

did you check the distributers on their site?

http://www.methacrylate-monomers.com/methacrylates/us/products/sheet_products/contactus/

http://www.methacrylate-monomers.com/methacrylates/us/products/sheet_products/locator/default.htm

Would be great to find someone in the us… cant be that hard

I did look at a few of them. (Ones who had a webpage), but I didnt see the endlighten.
I guess I can call people.

Tim Roth - 16 June 2008 12:29 PM

did you check the distributers on their site?

http://www.methacrylate-monomers.com/methacrylates/us/products/sheet_products/contactus/

http://www.methacrylate-monomers.com/methacrylates/us/products/sheet_products/locator/default.htm

Would be great to find someone in the us… cant be that hard

yeah, sometimes its still better to call people.. even with email/websites etc.

good luck and let me know, would like to post the source on my blog when you find one in the us

I e-mail professional plastics for a price quote. I’ll let you know the price when I get it. I asked for 1/4” (6mm) and 1/2” (12mm) in there full sheet size 120” x 80” and if they sell smaller sheets.

I had a thought in possibly combining FTIR and DI with this technique. In the lab we are experimenting with pulsing and syncing light to the camera. If there was a top thick piece of acrylic 1/2” (12mm) FTIR and then a piece of Endlighten (DI) directly under it, then we could oscillate between the two LED sources. Therefore can see the FTIR from the top sheet in one camera frame (DI/Endlighten lights off) and then next frame, turn the FTIR LEDs off and Endlighten ones on. If that makes sense.