At 10:15 PM 5/8/2001 -0400, Declan McCullagh wrote:
>On Tue, May 08, 2001 at 04:59:29PM -0500, Jim Choate wrote:
> > > For automated photolasers, mount a slave flash beside your plate.
> > > When the camera goes off, its flash will trigger yours, again dazzling
> > > the camera.
> >
> > Provided the camera isn't very fast. The responce time of your system and
> > the time of flight time of your flash will likely get there about the time
> > the shutter closes down. If it's CCD then forget it, you'll never get
> > enough of a window.
>
>If we assume ISO100 or equivalent film and a moderate telephoto lens,
>the camera is going to have to use a pretty fast shutter speed to
>avoid motion blur. I'd speculate it would be something like a few
>hundredths of a second -- I don't see why an electronic flash couldn't
>fire in that time.
It can, of course - that's what slave flash units do, and they do it
quickly enough to illuminate the subject while the shutter is open. In
fact, some of the red-light cameras themselves use slave flash units closer
to the car(s) to better illuminate the car(s) involved.
I'd expect them to be using much faster film, though - maybe something like
Fuji's 1600 speed color print film, perhaps pushed to a higher ASA. They've
got to be using a small aperture to maximize depth of field (want to get
lots of sharp detail), and the shutter speed's gotta be pretty fast, so the
only place to make up the difference is in film speed. Most modern cameras
fix the shutter speed at 1/90th of a second when electronic flash is used,
which is pretty slow, relative to the speed of light.
>A better question would be whether the flash would be sufficiently
>blinding -- if it were not aimed at the camera, it might have little
>effect. A decent (~$300) flash can throw a few dozen feet, but it's
>more directional than not.
Dunno. This page that Google cached might be of interest generally
regarding red light cameras - the original seems to be gone.
http://www.google.com/search?q=cache:www.co.ho.md.us/redlight.htm
