I found an issue with my IR bandpass filter. It appears to have a narrower FOV then my webcam. The blobs suddenly disappear as you near the edges of the display. It’s strange because the camera is still showing some light for these areas, but the 850 NM laser light gets completely cut off.

Very good!!!!but also to me ago thus, it is the circumference of the circle of webcam that it is round, you not to worry your job is wonderful, I I would not be never successful to make it, compliments. I but when I want to try demo the Flash serves OSC.exe in order to use them, only that OSC.exe me do not leave just you I have a copy?

Andry94 - 12 July 2008 03:43 PM

Very good!!!!but also to me ago thus, it is the circumference of the circle of webcam that it is round, you not to worry your job is wonderful, I I would not be never successful to make it, compliments. I but when I want to try demo the Flash serves OSC.exe in order to use them, only that OSC.exe me do not leave just you I have a copy?

Thanks, I can not use TouchLib OSC.exe yet because I can not run a calibration.  I am waiting for for an ffc extension to power up my LCD panel.

Looks like you may have to mod the camera lens holder so you can get the filter as close as possible to the lens.

Can you do that on your cam?

Tinkerman - 12 July 2008 05:18 PM

Looks like you may have to mod the camera lens holder so you can get the filter as close as possible to the lens.

Can you do that on your cam?

No, the filter is touching the lens.

The only thing i can think of is replacing your lens in webcam with a wide angle or fish eye lens so you camera sees more in the “active” region of the BP filter… or you have to get a BP filter with a larger diameter.

Taha

Taha - 12 July 2008 05:58 PM

The only thing i can think of is replacing your lens in webcam with a wide angle or fish eye lens so you camera sees more in the “active” region of the BP filter… or you have to get a BP filter with a larger diameter.
Taha

The problem with the Creative VF0070 camera is that the lens is very difficult to remove.  However, for now I can use the digital zoom and pan that comes with the camera to narrow the camera’s FOV.  Unfortunately, this will lower my resolution and I will have to increase the camera’s distance from the display.  I bought the VF0070 because of the wide angle lens so I could get the camera closer to the display.

rdagger - 12 July 2008 08:37 PM

Taha - 12 July 2008 05:58 PM

The only thing i can think of is replacing your lens in webcam with a wide angle or fish eye lens so you camera sees more in the “active” region of the BP filter… or you have to get a BP filter with a larger diameter.
Taha

The problem with the Creative VF0070 camera is that the lens is very difficult to remove.  However, for now I can use the digital zoom and pan that comes with the camera to narrow the camera’s FOV.  Unfortunately, this will lower my resolution and I will have to increase the camera’s distance from the display.  I bought the VF0070 because of the wide angle lens so I could get the camera closer to the display.

If your filter is IR interference type filter, this can be the problem.
The thing here to note that interference filters shift their CWB based on the incoming light angle.

~Alex

AlexP - 13 July 2008 03:59 PM

If your filter is IR interference type filter, this can be the problem.
The thing here to note that interference filters shift their CWB based on the incoming light angle.
~Alex

You’re right, I do have an interference filter.  What type of bandpass filter do you think would work best?

I have done more research into the problems with my narrow bandpass filter.  It turns out that there is no perfect filter for MT applications, but there are several approaches to improve efficiency.  I think the problem with narrow intereference filters is that they shift blue as the angle of the light gets farther from the zero angle of instance.  Therefore, the center of what you are filming gets excellent pass but fails toward the edges.  So the first thing you need to do is calculate the FOV angle of what your are filming to determine how much blue shift you are going to get off center.  Then you can select a CWL that is higher than the wavelength of your LED’s or lasers.  This red shift will compensate for the blue shift and provide a good pass near the edges of your table.  However, you will have to increase the FWHM to compensate for the shifted CWL.  Otherwise the center of your table will have poor pass.
For example, I have 850 nm lasers and a webcam with a wide angle lens.  Assuming a 40 nm blue shift at the edges of my table, I might select a bandpass filter with an 870 nm cwl because at the edges of my table it is effectively an 830 nm filter.  I would then select an FWHM of around 50 to give me an effective range at the center of the table between 845 and 895 nm and 805 and 855 nm at the edges.
Some concerns are that there might be inconsistant intensity at different angles.  This could addressed by increasing laser power to increase its overall relative brightness to the ambient lighting.
Other steps to improve the blobs is to decrease the FOV of the camera lens (less wideangle) although this requires you to have the camera farther from the display.
I’m not an expert so if I misinterpeted anything please let me know.

I believe this effect is due to the Cos4 Law Of Illumination Fall Off.

States that light fall-off in peripheral areas of the image increases as the angle of view increases, even if the lens is completely free of vignetting. The peripheral image is formed by groups of light rays entering the lens at a certain angle with respect to the optical axis, and the amount of light fall-off is proportional to the cosine of that angle raised to the fourth power. As this is a law of physics, it cannot be avoided. However, with wide-angle lenses having a large angle of view, decreases in peripheral illumination can be prevented by increasing the lens\’ aperture efficiency (ratio of the area of the on-axis entrance pupil to the area of the off-axis entrance pupil).

I’m not sure exactly how that solution translates to digital video.