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Webcam photography without infra-red

Hurry!

At the moment, the 360,000 pixel light sensors used for most webcams are still a reasonable size - around a quarter of an inch square. The next 'leap forward' in technology will be to make the pixels smaller, and cut the size of the sensor. The result will be unusable for any serious photographic purposes, but it will cut the cost, and as we all know, that is all that matters. If you anticipate looking at this aspect of photography, buy, for example a Kodak DVC325 webcam as soon as you can, as cheap as you can. Get it running for test purposes, assuming you have Win 98SE or later and a working USB port, then put it away until you have time available.

Basics

Inside the cheap plastic body of the Kodak DVC325 webcam, and others, is a remarkably good imaging chip. The lens provided actually focuses, and Kodak has worked harder than most on the optical quality. The main priority is moving pictures in low (household) ambient light, so the lens has a wide aperture, and at this price, no means of stopping down. Central definition is marvellous, considering the cost, but outside the centre things soften up fast. All costlier digital cameras incorporate the lens so closely into the design that there is no chance of removing it, making them useless for serious technical photography. If you ignore the warranty, you can remove a webcam lens, leaving behind a convenient image sensor that can send 640 x 480 colour images via the USB port to your computer. You can then hook up whatever optical system you like to generate images on the sensor.

The infra-red snag

Assuming you know enough about building cameras to eliminate light that does not come in through your lens, and have internally baffled your optics to intercept stray light and reflections, you will still be very disappointed with the images on your monitor. The focused images will of course be sharp, but the nice colour rendition of the Kodak lens will be replaced by a low-contrast picture rendered in various shades of purple. The webcam sensor is acutely sensitive, like most silicon optical chips, to infra-red. If you look at the back element of the Kodak lens, you will see the surface has a very strong red cast. This is a high-tech interference filter that removes infra-red, and probably costs at least 5 cents to apply in bulk quantities. If you find, and purchase a similar filter deposited on glass, you will be paying more for it than the webcam. Plainly this does not appeal.

The answer is not to try and remove the infra-red, but to confine yourself to photography where the light sources have no infra-red in them. For a start that means no outdoor light, and no normal tungsten 'lightbulb' light either. All the photos of the 'burrlight' in the camping section, and the ledlyt installation in this section, were taken with a heavily-modified DVC325 webcam. Lighting was a combination of short fluorescent tubes, and two of the new electronic 'cold lights' sold to cut power consumption in normal tungsten light sockets. These are essentially mini-fluorescents. All these use discharge tubes, and generate close to zero infra-red. Provided your room is curtained against daylight (photography at night is easiest) and tungsten light is not leaking in from other rooms, your monitor pictures are once more clean, sharp and coloured.

Some camera information

Required resolution by your lens system, for a good sharp picture, needs to be better than 200 lines per millimetre at this sensor size, and not many lenses can do this. I removed the click-in front panel from a DVC325, and fibreglassed on a small piece of the laminated material used for surfboard fins. Both the laminated material and the fibreglassing resin had to be styrene monomer based rather than the more commonly used epoxy, so the styrene would dissolve its way into the plastic body of the DVC325 and set when hard to a 'cold weld'.

Once I had a laminated panel with a central hole to admit light to the sensor, I drilled three holes in the panel and three setscrews in the holes provided a three-point mounting for an aluminium lens panel. I used a red laser pointer reflecting off the face of the image sensor to set the lens panel accurately parallel to it using the three screw mounting. This process is known as collimation. Either read a book on the subject, or follow my example and work it out for yourself. Once the panel was aligned, I used two short Pentax screw extension tubes locked on the panel, so the webcam now took Pentax screw lenses. All lenses are of course 'extreme telephoto' with this image size. Most of the pictures are taken with a 35 mm f3.5 moderately wide angle (original Pentax of course, nothing else is nearly sharp enough). Real close-ups like the business end of the ledlyt tube, use a Pentax 50 mm f4 macro lens, since the corrections on the wide-angle start to expire when used this close.

Once the webcam takes Pentax screw, photomicrography presents no problems either. All that is needed is a Pentax screw microscope adaptor to connect your webcam and the microscope eyepiece tube. The eyepiece of course comes out, so you are working on the primary image from your objective, and flare from the eyepiece tube internal plating will completely ruin your picture unless you remember to drop in the Pentax-provided matt-black tube insert to cover it.

Ledlyt illumination

Once your webcam is set up, you need, of course, a ledlyt illuminator on the microscope, since otherwise the image is awash with infra-red. With the ledlyt, what you see is what you get, and you can run a whole session involving multiple slides without ever looking through an eyepiece. The webcam can be used for monitor display to a teaching class if you do not need permanent recorded pictures.

Harsh reality

If you use the DVC325, and set it up as the book and CD tell you, even on a computer with a decent (faster that 200 Mhz) processor, you will find the USB has a tendency to crash. Even with a fast video card, the video link is not really quick enough for good focusing, or target selection on the slide. Go to the Kodak website, and look around for an updated driver for the DVC325. Download this, set it up as instructed, and suddenly the system is very close to adequate. We use this system with Windows 98 SE on both a Toshiba Satellite Pro 490CDT laptop, and a built-up tower machine with a 400 Mhz AMD K6-2 processor, a Tyan motherboard, and a fast but obsolete Quantum Raven PCI video card. The on-board Tyan USB port was buggy. I had to disable it, and plug in an additional PCI D-link USB port, before the pictures started to flow.