I’ve just finished building my first FTIR prototype, using some 6mm thick acrylic (http://rswww.com/cgi-bin/bv/rswww/searchBrowseAction.do?N=0&Ntk=I18NAll&Ntt=825-253) and 20 5mm IR leds (http://www.maplin.co.uk/Media/PDFs/yh70m.pdf). The LEDs seem to work just fine, and if I set my camera up opposite them, they look like this:

However when I place my (polished) acrylic next to the LED array and place my finger(s) on the acrylic, no IR light seems to be reflected out the back of the acrylic.

Does anyone have any ideas?

Thanks in advance!

has your camera’s ir filter been removed?

Yes, it has been removed. The camera picks up the light from the LEDs when I point it straight at them, it just wont pick up any light from behind the acrylic.

hmmm...so you say the edge has been sanded and polished.

and u get not even the slightest ir reflecting…

try holding the camera as close as possible to the area which has been pressed,maybe the led’s arent strong enough?
if there’s still nothing hop onto #ftir on irc.freenode.net. maybe someone there can help more.

Something is wrong with your camera/lens.  A camera with the IR filter removed will basically white out 50% of the screen when you point the LED straight at them.

Your images look like what my camera saw when it was unmodified (IR filter still intact).

What camera are you using?

It’s the Logitech Quickcam Express. I’m almost certain I removed the IR filter, there was a small piece of red plastic inside the lens which I took out. With it in, pointing my TV remote at the camera did nothing, after removing it, a white light was visible.

For further clarification, the view from my window looks like:

Get your fingers wet and touch the acrylic.

Your camera doesnt seem to be sensitive to IR light.  The outside image is very dull.

Are you sure you dont have an option set so it has very low brightness or something?

As suggested on IRC, I purchased the Phillips webcam, a new lens from ebay, and a high-pass filter. Blobs are now showing up perfectly. All I need now is a compliant surface. Did anyone ever discover if the DDR pads worked or not? http://www.amazon.com/gp/product/B000CSBVBM/ref=olp_product_details/002-3447323-2135222?ie=UTF8

I heard that gravano is no longer selling silicone surfaces, is this true? Has anyone found another supplier?

good to hear that it’s working now. yeah,i also heard that,although i think gravano is just not taking new orders right now.

maybe there is a guide on making one under compliant surfaces?otherwise,ask him,maybe he can tell you how.

The ddr pads work, but they have a really, really visible texture on the projection. It makes
it totally unsuable for me. I posted some pictures in the thread discussing the ddr pad.
Take a look, and you´ll see waht I mean. BTW. another really great compliant surface is
plain olive oil The blobs are totally awsome, but again not really practical
I put the projection screen on the bottom side of the acrylic and the oil on top..
Really, silicone rubber is the only real alternative right now..

that’s funny.  i tried olive oil and mylar a while back.  all i got was a mess. :(