Film Negative as a Visible Light Filter

This is why I decided to buy 850nm IR lasers instead of a different wavelength:

Color Film Negative Makes Visible Light Blocking Filter: http://www.discovercircuits.com/H-Corner/color-neg.htm

Since the camera in my touch table needs to only see IR light, I had to first remove its IR filter so it can see EVERYTHING, then use DEVELOPED film negatives to block most of the visible light.  This is a common tactic in the community, but now behold… a graph.

The film negative has to be exposed and then developed.  I held it up to a fluorescent light for 30ish seconds to effectively take a picture that was all white.  Then when you get it developed, the negatives will be all black.  I had no luck at Wal-Mart, they don’t have a film processing machine anymore, at least not the one I went to. CVS did it, but they did not understand why I didn’t want any pictures and only negatives.

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