A Camera

First, take a perfectly ordinary USB camera. This is a lovely little device, with a tiny CCD image sensor - much, much smaller than the image area of a 35mm negative. The reasoning goes that if the image sensor area is only a small fraction of the size of a 35mm negative, then it will provide a natural telephoto effect - attach a 50mm lens, and you will get the equivalent of a 200mm or so lens.

So... remove the casing from the camera module. You're left with a circuit board with detector, and a small lens pushed on the front. Remove the lens. Now go & find your old 35mm SLR camera. Take off a lens, and check out the bayonet mounting. Find a slab of Aluminium alloy of the right thickness (I used the backing plate from an old QIC cartridge). Mark out from the lens, then cut, drill and file, until you have converted that plate into a bayonet mounting for your lens.

Now the fun bit... attach the plate to a suitable base plate (I found a scrap of old Contiboard worked well). Bodge together some form of tripod mounting (I used some 22mm water pipe to make a nice "pan and tilt" type mounting). Carefully position the circuit board from the USB camera at the focal point of the lens. Now all it needs is a little light-tighting, and away you go!

My first attempts used a kitchen towel and suit jacket to cut out stray light. This wasn't terribly convenient, particularly when anyone wanted to dry their hands. But it did have the advantage of looking like a strange cyclops! The New Improved model uses the cardboard from a box of Special K (you may find that other cereals will work as well), plus copious amounts of masking tape and warehouse tape. It would have been a good idea to paint the inner surfaces black first.

So - the results. Well, I was very worried about the purple tinge to all the foliage in my outdoor shots. At first I put it down to light leakage through thetowel (hence the upgraded Special K lightproofing). Then I wondered whether the CCD is spot on the focal point of the lens (it isn't, but I don't think that affects colour - sharpness, maybe, but not colour). I am now pretty well convinced that it's due to the camera picking up infrared - I think the original plastic lens blocks out IR. This is supported by the way in which car brake lights, candles etc seem overbright in the image. I need to try a few nightshots to confirm this.

They all show a little blurriness compared with the standard lens. Some of the blurriness in the out-of-the-front-window pictures are because of out-of-focus foliage in front of the subject (I really must prune that Wigelia). I think also that not having blacked-out the inside of the camera means that there is a fair bit of light bouncing around inside. And I'm pretty certain that the CCD isn't in precisely the correct position or orientation (it is, after all, merely wedged against a bit of wood and held down with masking tape).

The following shots are taken either with the original lens (ie they are what you would see from an unaltered webcam), or a 50mm Rollei lens, or an 80-200 zoom lens set at either the 80mm or the 200mm setting. In each case, I have just cut out part (320 x 240 pixels) of the image rather than giving you the full 640x480, to make for a smaller web page. But I haven't digitally zoomed or otherwise altered the images.

From the front window - unaltered webcam	From the front window - 50mm lens
From the front window - 80mm lens	From the front window - 200mm lens

The distance from the camera to the "Return to High Street" sign is approximately 80m

Looking towards the kitchen spice rack unaltered webcam	Spice rack - 50mm lens (or was it the zoom set at 80mm?)
Spice rack - 200mm lens

The distance from the camera to the mustard is approximately 7m