using camera flasher for CMOS sensor illumination.

As the name implies, a flasher isn't for continuous operation. It puts out a high intensity for a short time. Trying to flash it at 580 / sec might make it explode if the intensity was high. Maybe you could use a ring of high intensity white LEDs around and just behind the sensor, maybe with a diffuser, to get even illumination of the object.

-- John

On a sunny day (13 Apr 2007 03:58:09 -0700) it happened snipped-for-privacy@millenniumit.com wrote in :

A flash that operates at 580 flashes per second is a stoboscope (and a fast one). However the CMOS sensor has an exposure time, and the stroboscope would need to be synchronized with it. Also a 'flash' does _not_ guarantee uniform lighting. To sync the stroboscope wit hteh sensor would requrie electronics and likely some programming (embedded), if at all possible, things like flash duration, light output curve, CCD shutter time etc need to be looked at. So perhaps it would be much simpler to add some extra normal lightsources to light out your object.

Flash tubes aren't designed to stay on - they burn out if you try.

A short arc xenon lamp or short arc mercury lamp would work - but you may have to filter out the UV or risk bleaching the gray scale target.

A circular fluorescent lamp at close proximity to the target and around the sensor might be another cheaper alternative. - I used a fluorescent lamp for a "dark field light box" I built, along with a cmos camera and ran into a problem with "aliasing," 60 hertz flicker of the light was in and out of sync with the camera's vertical sampling.

The company with the software was not willing to modify their design to average the images over time (one solution) for a reasonable cost, so I ended up using four tubular aquarium bulbs to provide illumination and had to add a timer so the thing wouldn't cook itself to destruction if someone forgot to turn it off (160 watts)

I should have stuck with the fluorescent and made a high frequency ballast for it, but the light box was wanted in the lab and they wouldn't let me tinker with it.

To make a more uniform field with LEDs, choose wide-angle or unlensed types, use many of them, extending over and beyond the desired coverage area. If results are not uniform enough, add some sort of scattering element in between. The prismatic plastic sheet material used with fluorescent lighting fixtures (troffers) has lower losses than milky diffusers. Finally, consider using processing to deal with the non-uniformities. Some imager chips do this for you. Paul Mathews

A block of LEDs the size of your target, or as big as needed to make a uniform light on it, with the camera looking through a hole in the middle of it.

Colin =^.^=

Look at Xenon discharge lights. Small units are available for bicycles, while slightly larger units, are used as car headlights. Basically, a 'flasher', is a Xenon light, giving high intensity for a short time. However the tubes are not designed for continuous operation, and will overheat if driven continuously. Units designed for continuous repeat operation, are those used in stroboscopes, while the units designed for continuous operation, are the Xenon discharge lights. You are going to have to design carefully, to get even illumination though. This is why professional photographers, will have multiple lamps, and diffusers. What about a EL panel?.

Best Wishes

I had to do this very same thing for a client not to long ago, only I used the Micron sensor instead. We only needed the IR band.

I ended up using a large grid of IR LEDs. The trick was spacing them for even light. Our ID dude helped, and armed with the dispersion angle of the LEDS and the distance (luckily fixed) the image he suggested the spacing to use, which was close enough. There was some 512 - 768 (I don't remember anymore it was almost 2 years ago) LEDs to the array. The distance was about 18" or so.

This replaced a photo flash system that used 4 flashes and gave more even light than it did.

Good luck. Hawker

On 4/13/2007 6:58 AM, The digits of snipped-for-privacy@millenniumit.com's hands composed the following:

no, it'd probably melt or explode.

Some automotive lamps are labeled as xenon lamps, you could try them, (I only mention it because xenon discharge tubes are the camera flash)

or just a regular spotlamp, halogen, incandescent, stage lighting, or whatever.

The output of a projector (eg slide projector) is a very uniform field too. (especially if you replace the AC supply to the lamp with regulated DC)

Or the sun if you can get suitable weather and work in the sun or arrange a heliostat.

Bye. Jasen

No. It'll overheat.

You're going to find it extremely difficult to flash a Xenon tube at that rate. LEDs will handle it easily, & can be pulsed at much higher currents than can be used for continuous illumination.

The reason you can get a fairly flat field from a camera flash is that the reflector has been designed very carefully. The easiest solution I can think of for your problem is to do the same for a housing for a bunch of LEDs.

Indeed. And for small subjects, up close (which is what the OP seems to be talking about), you'd normally use a ring-flash, which is typically a pair of 1/2 circle xenon tubes or a ring of LEDs in the shape of a doughnut, that fits around the lens itself.