Infrared Camera Conversion

With my brother’s wedding approaching, I decided to tackle a project that had been on my list for a long time: converting my old Nikon D70 SLR camera to shoot infrared photos.

Infrared light falls beyond the color red in the color spectrum and is invisible to the naked eye. While anything hotter than its surrounding environment emits infrared light (which is how thermal cameras can see in the dark,) the most common use is so your TV remote control can communicate with your TV.  Infrared Photographs are completely different, and can make for some eerily beautiful shots.  The sky appears dark because it doesn’t emit much heat, but plants do so they are bright.

All digital camera sensors are sensitive to infrared light, but manufacturers include a “hot filter” to filter most of it out. Some sensitivity remains however. You can demonstrate this by photographing your TV remote while holding a button down.  Your eye won’t see anything, but you’ll see the glow of the infrared led in the photograph.  Since the hot filter does not perfectly filter infrared light you can indeed make an infrared photo by placing an opaque filter in front of the camera. The downside is that the exposure needs to be a minute or more to collect enough light through the hot filter to make a decent shot.” This method is alright for landscape photography, but doesn’t work if anything in the scene is likely to move during the exposure.

The solution to this is to modify the camera, removing the “hot filter” and replacing it with an opaque filter that blocks visible light but allows infrared light through. There are a variety of services online that will perform this conversion for you, but we have already established that I have no fear of taking things apart, so I forged ahead.

First I needed the actual filter. Based on information online, I chose the Edmund Optics (a division of Edmund Scientific) Optcast IR filter. It was 2″x2″ in size and was fairly cheap so I ordered two knowing that I would have to cut it down to 29.59mm x 25.27mm and wanted to have more than one attempt. This was before I had the laser cutter so figured I would be cutting it with a knife and sandpaper. Naturally since I now had a laser, I would use it for this task. The material appeared to be a polycarbonate since it released a goo when cut, it was interesting though, you could see through it from the edge but not from the flat surface. So it looked like it was clear material with an opaque film on both sides. I ended up using both filter pieces as I had to do some experimentation to figure out how much of the material the cutting beam removed and increase the dimensions to compensate. I almost lost the second piece because I entered the wrong dimensions for the final cut (top left corner), but fortunately it left enough to cut the final piece in the remaining material (bottom right.)

From that point, I followed Matt’s excellent instructions on the IR Photography Forums which were flawless, right down to the problem I had when I initially reassembled it and found it wouldn’t record any photos. When he says it’s easy for the ribbon cable to not get inserted fully during reassembly, he’s not kidding. After two additional attempts, I finally got it right and it works wonderfully.

After conversion, you can rely on the built-in light meter to set the shutter speed which is nice. To get photos like those shown, you set the white balance by measuring something grass green in color. The thing I’m still learning about is focus. Infrared light actually focuses slightly differently in lenses optimized for visible light. In the past, lenses included a line for IR. You focused as normal, then turned the focus to the nearest point on that line. Some IR conversion services can adjust the auto-focus to account for this, but the DIY methods aren’t well documented, probably because they aren’t reliable.  But at higher f-stops, this makes less of a difference. Photos of people are interesting because the skin emits IR and appears to glow. One of my favorite pictures is looking up through tree branches because the branches themselves don’t emit much IR, but the leaves do.

As a side note, you can remove the hot filter and not replace it with an opaque one. In this case it would record both visible and IR light. Typically you would use a filter mounted on the lens to make the camera shoot IR or natural light. But I purchased an upgraded camera and kept this one specifically for this purpose.