Ask Slashdot: Anti-Camera Device For Use In a Small Bus? 478
Paul server guy writes "I am building a limousine bus, and the owners want to prevent occupants from using cameras on board. (But they would like the cameras mounted on the bus to continue to operate; I think they would consider this optional.) They would also like to do it without having to wear any 'anti-paparazzi' clothing (because they also want to protect the other guests on board), and without destroying the cameras. (So no EMP generators, please). We've done some testing with high-power IR, but that proved ineffective. Does anyone have any ideas that they are willing to share?"
Re:Makes no sense. (Score:4, Informative)
Re:Problems (Score:5, Informative)
1. Detection rather than nullification. Maybe you can't prevent but you can at least know when,
Detection of the camera pointed in the unknown direction on the bus will be impossible.
2. Maybe you can use IR to fool the autofocus to one extreme or another?
Nearly all SLRs are insensitive to IR light when recording. And almost no camera today (still or video) is using IR to autofocus. Illuminating the area with a powerful IR light is damaging to the eyes -- yes it is like regular light except in the dark when the pupils are be dilated any powerful light can cause a damage. I was working on a device that had 3W IR LEDs and after a few minutes the eyes begin to hurt even when I was not looking at the lights directly.
Re:Makes no sense. (Score:4, Informative)
Keeping the limo's own camera working is probably the easiest part, as just about any scheme you come up with to stop cameras from working has a way to defeat it. And it isn't that difficult to come up with schemes that, while having easy ways to keep a specially designed camera working, stop some generic cameras. The hard part is finding something that will affect a majority of cameras, especially non-cheap ones, while not impacting the passengers' eyes or other devices around they may want to use.
Some cheap cameras can be defeated with enough IR of the right wavelengths, while not being dangerous to eyes, and it would be really easy to filter out in your own camera. But a lot of cameras are have much better IR filters than they used to, and with better light sensitivity means shorter exposures (and hence more difficult to use an IR strobe light). I've had unintentionally caused problems with various digital cameras before by having a near by spark gap firing that tends to cause a lot static to show up on sensors. But that is going to depend on the housing of the camera is built, and some cameras are fine off the shelf. Of course if the lighting inside the limo is bad, so longer exposures are needed, the cameras may become more sensitive to such issues, assuming the intended customer base sees bad lighting as a feature and not a fault.
Not UV [Re:Sure it makes sense] (Score:5, Informative)
Limo owner wants a defense in case something illegal happens or damage occurs.
Partiers want protection from each other - that no one will publish pictures so they can party freely.
Diffuse but relatively bright UV, implemented with either UV fluorescent tubes or UV LEDs should do the trick. Fit your own cameras with UV filters. Regular cameras will work, but will be affected by a strong 'white haze'.
The bright but diffuse UV should not be harmful to eyes for shorter intervals. Be careful about that, however.
UV??? wouldn't be my first choice. If it's bright enough to haze the image in a camera, it's bright enough to be dangerous if you look into the source-- and if you're doing this without clear warming, you can expect at random some people will be looking at the source.
The problem with UV is that, in any wavelength that's not absorbed by air, you're still only getting one electron per photon on the CCD detectors. So, since the photons are so energetic, it is terribly energy inefficient as a way to overexpose a CCD. You have to pump out a lot of UV to overload a CCD, and that's dangerous.
IR is much better choice-- the photons are low energy, so you're in the opposite regime. Use a wavelength of about 1 micrometer, and you can't see it, but the CCDs can.
Other than that solution, I think you're out of luck.
Beware of nicer cameras which might be fitted with a UV filter. They are common.
Yes, that's another flaw. Most professional-level photographers keep UV filters on their cameras just as a matter of course.