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11-09-2009
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The IXUS 850IS before the conversion
25-9-2009
Modifying a camera to make infrared pictures.
Because the resolution of my old infrared camera does only allow small prints. Because I bought a new camera for walking around I had a Canon IXUS 850 IS that was doomed to gather dust. I inspected the camera and when I saw it might be easy to modify to take infrared pictures I decided to try modifying it.
This modification means the infrared blocking filter (hot mirror) that is in the camera right in front of the sensor must be removed to make the camera sensitive for infrared light. After removal, the filter must be replaced with a filter that passes infrared light and blocks visible light. These filters are completely black for the eye but it is quite difficult (impossible) to find one with the right dimensions and thickness for a reasonable price.
The back of the camera removed
The solution is to use ordinary slide film. Slide film does pass infrared light to prevent it from getting too hot in a slide projector (these things that were used to bore people for many long evenings). So unexposed but developed slide film would become my infrared filter.
The darker the film, the better it blocks visible light. So I went out to the shop to get a medium format roll of Fuji Velvia 100F, a film that is known for it's deep blacks. Be prepared to explain to the people in the shop that you are not crazy and do know something about photography when you ask them to develop the film that not even left the packaging...
A few days later you can pick-up your developed film that turned into a completely dark strip, large enough to cut out many infrared filters.
Now we had to open the camera. Fortunately this was an easy job, just use a small screwdriver to remove the few even smaller screws. Some of the screws are hidden but not hard to find. When all the screws were removed the back could be removed without force.
After the screen was removed
The next step was to remove the screen. To my surprise the screen was not fixed by screws or any other firm fixation, instead it was not fixed at all. To lift it far enough, like in the picture, it was enough to remove the wires from the connector at the top of the camera. With help of some pointy tweezers no problem at all.
Under the screen we see a metal plate which is fixed with three screws which are secured with some lacquer. on the other side of this plate we will find the sensor.
These three screws are important because they do not only hold the sensor in its place but they also hold the front of the sensor in the plane of focus of the lens. Three springs under the plate push it backwards against the screws. Loosening one of the three screws will tilt the sensor at that point backwards.
First I removed the lacquer with a little swab with some ethanol. To ensure the sensor will be fitted back at the same position I mark the position of the screws and count the turns needed to remove them. It is important to remember the position of each screw or my marking and counting activities would have been useless. It is also important to rember there are springs under the plate when you remove it. These little springs tend to escape very easily when they are suddenly released from their little pockets.
The sensor removed
After I removed the sensor, I could see the infrared blocking filter right below it. The filter was much larger than the sensor and mounted by four little drops of adhesive which I removed with a surgica knife.
Now the filter was removed I could measure its dimensions so I could cut the same size from the slide film. The filter was very thin, about 0.2mm. This is a good thing because the filter need to be replaced with a filter with more or less the same optical thickness to keep the ability to focus at infinity.
I decided to replace the glass filter with two layers of film to get an even darker filter and still keep the ability to focus at infinity. After all, the darker, the better was our slogan.
After some creative work with my film and scissors I had two pieces of unscratched film that should do the job. I mounted the two pieces of film with four drops of lacquer to fixate it.
The camera after assembly, the old filter in the front
Assembling the camera again is not very exiting. It is just doing all disassembly steps in reverse order.
On the picture of the assembled camera, the infrared blocking filter can be seen in the foreground. I will keep it although I do not expect that it will be put back in the camera.
After taking some pictures to test if the camera was working OK and if it still focused at infinity it was time to look if we could make it even more fun. I found out that the flash output did contain enough infrared light to be usable. Because the visible light from the flash would not be needed, it could just as well be blocked. This explains the piece of film that is taped in front of the flash. Now it is possible to make infrared pictures in pitch dark without distracting the scene with flashlight.
This of course does open new opportunities to use an even larger flash with a slave trigger but that might be something for a later project.
A first test result from the modified camera
Then it became time for some infrared picture taking. Here is a first test picture. It shows clearly the white leaves of the trees that is characteristic for infrared pictures.
The infrared section in the gallery does contain only pictures from the old Ricoh Caplio G4 wide but soon I will add some pictures of the Canon to the infrared gallery.