Seems like the filter is 850BP20 making the lower cut off 830 and the upper cut-off 870
Taha
No, I’m no expert but based on the CWL and HBW I think the passband would be 845.15 to 857.05.
The width of the passband (HBW) is defined as the difference between the two wavelengths at which the transmittance is half the peak value.
Here are the results of my outdoor test with my 850 NM bandpass filter. The 2nd pic shows my rig which consists of 2 sawhorses, 2 lasers, a webcam and an LCD panel. This test was performed on a bright smoggy California day around 11 AM with the sun almost overhead and shining down directly on the LCD panel. The first picture is without filter and the last picture is with filter. This test was a failure. In full direct sun light, I am not getting any blobs. This test was hard to perform because I could barely read my laptop.
My next test is outdoor, but with partial sun. I slid the rig over about 10 feet out of the direct sunlight. However, the area is still flooded with ambient sun light. The first picture shows the new position of the rig. The next picture is without an IR filter. The last picture is with the IR bandpass filter. These results are better. They are not even close to the indoor tests. Still, without the IR bandpass filter there are no blobs and with the filter there are blobs despite the sunlight. Please note that I was in a hurry and these tests were performed without calibrating the laser positioning. Hopefully, after I build a proper enclosure, the rig will work better outside.
Hmm , well it’s way better than DI in sunlight , ) but FTIR with a decent bandpass gives out quite similar results , this is not what everyone was hoping for but it’s something.
Here is a new test performed at around 8:30 AM with my rig set up indoors next to an east facing window. The first pic shows the sun shining through onto the table. For this test I am using a 1/4” piece of acrylic instead of an LCD panel (the acrylic still has the protective coating which is scratched up). The laser height has been calibrated to project a line beam directly above the acrylic. I also used a secondary IR camera to insure the beam was parallel to the acrylic and to verify the height. The two 850 NM lasers are placed in the top left and bottom left corners. The 2nd pic shows the table top. The next picture demonstrates the IR camera without any filter. The last pic shows the improved blobs with an 850 NM bandpass filter.
I’m fairly new to this still, but I’m just wondering.. If you have the webcam with a bandpass filter of 850nm, 850 nm lasers, and on top of the touching screen have a filter that blocks all IR light (which I know you don’t have atm) from coming inside the box (I realise that you don’t have an enclosed box, but let’s just say you do:p ) And also this requires the lasers to either be setup as a FTIR setup. Won’t then the blobs from your fingers pressing against the IR blocking filter be shown for the camera and nothing else? Even in direct sunlight. I mean, since the camera only sees 850nm wavelength and the box doesn’t let in or out and kind of IR light. Only if you push your fingers agains’t the screen and the light is reflected downwords, towards the camera.. Correct me if I’m wrong or if I explained something badly
But you guys see what I mean with the IR blocking filter completely covering the touching area which is the only place light can go in and out of the box..
I’m fairly new to this still, but I’m just wondering.. If you have the webcam with a bandpass filter of 850nm, 850 nm lasers, and on top of the touching screen have a filter that blocks all IR light (which I know you don’t have atm) from coming inside the box (I realise that you don’t have an enclosed box, but let’s just say you do:p ) And also this requires the lasers to either be setup as a FTIR setup. Won’t then the blobs from your fingers pressing against the IR blocking filter be shown for the camera and nothing else? Even in direct sunlight. I mean, since the camera only sees 850nm wavelength and the box doesn’t let in or out and kind of IR light. Only if you push your fingers agains’t the screen and the light is reflected downwords, towards the camera.. Correct me if I’m wrong or if I explained something badly
But you guys see what I mean with the IR blocking filter completely covering the touching area which is the only place light can go in and out of the box..
Assuming FTIR , anyone have any suggestions on what to use to block all IR light on top of the screen?
Rosco blocks some IR, thats why its used a projection screen for FTIR… as well as there are various IR blocking films available… but perform on only so so nothing really great
Rosco won’t block ALL IR though and still lets in way too much IR for daylight use. I’m not sure of anything that’ll block ALL IR and still allow for projection.
