"ChronoFish" <deja@chronofish.com> wrote in message news:9544e856.0309201910.3cc5574a@posting.google.com...

> Sorry to intrude on this group - I don't even own a video camera. I am

> not sure exactly what my question is, so I'm not sure how to best

> search through the archives...

>

> From my limited research and understanding, most digital cameras

> pickup near-infrared. With a simple filter you can block out the

> visable light so that the camera is only picking up IR. At night or

> inside you would need to use some sort of IR light to shine on the

> subject in order for the camera to pick it up, and then we are talking

> about subjects that are within 45 feet or so. I imagine this depends

> on the power of the IR light and the ability of the camera.

> So far so good.

>

> What I would like to know is if this is possible during daylight.

> That is I want the same affect - to only pickup subjects in daylight

> that have an IR light shinning on them. Would it be possible to use a

> second filter that blocks the IR from the sun (maybe the sun's IR is

> at a lower wavelength than the IR flashlight for instance). It's

> quite possible that IR is not the solution here, so I am open to other

> ideas as well.

>

> My requirements are simply to find an inexpensive way (cost of a

> consumer digital camera or less) to record subjects up to 30 feet away

> (further would be better, but definately 1 to 30 feet) based on where

> a "spot-light" of somesort is shinning.

Hmmm...

Probably not with IR...

CCDs are quite sensitive to IR, but during daylight, IR is present

along with visible light. Normally, an IR-blocking filter is used

in front of the CCD to permit predominant illumination from visible

light - and "night-shot" camcorders remove this filter to increase

sensitivity in low light, and to permit use of an IR source for

"invisible" illumination. Some cameras operate in this mode in

daylight (see www.David-Ruether-Photography.com/ir.htm for examples of

what this looks like), but it would be difficult to block visible

and some IR to use a strong beam of a different IR band to

illuminate part of the subject. It would probably be more practical

in daylight to use a beam of visible light that is strong enough to

overwhelm by a few stops the ambient light (such as using a

too-strong flash can do in bad wedding photography...;-). The

solution is likely just that: forget about IR and just use a powerful

flash with a controllable angle (use a "snoot" on it...).

--

David Ruether

d_ruether@hotmail.com

http://www.David-Ruether-Photography.com