Category Archives: science

Infrared Camera Hacking I. Coolpix 995

I’ve been wanting to get an infrared camera, mostly to try to document diatom growth in the intertidal and in lab experiments.

This is following a really neat article

Field-based remote sensing of intertidal epilithic chlorophyll: Techniques using specialized and conventional digital cameras
R.J. Murphy, A.J. Underwooda, and A.C. Jackson
( doi:10.1016/j.jembe.2009.09.002)

I picked up a Coolpix 995 on ebay for about $50, which seemed like a good one to start with. Actually in retrospect, I probably wouldn’t use a coolpix again because trying to control this camera directly from a computer turns out to be a nightmare. What it did have going for it is a good bit of documentation about how to pull the hot mirror out.

Pulling the hot mirror (also known as the IR cut filter) out allows the CCD to see all those wavelengths beyond about 700 nm that the mirror is there to block. It isn’t as simple as just pulling it out, though. For one thing, the filter is integral to the lens/CCD assembly. It holds the lens the proper distance from the chip. Pulling it thus leaves the whole optical path out of focus. Thus, it is essential to replace it with something the correct thickness.

Most people want to replace the IR cut filter with a long-pass filter to get rid of visible light. I just wanted it clear so I could swap filters out over the lens and see either visible or IR.

The best sites are here:
LifePixel
http://www.lifepixel.com/ir-tutorials/nikon-coolpix-995-digital-infrared-conversion-instructions.htm
These folks will do the conversion for you for a not-outrageous sum. They also sell filters that will fit perfectly, which would have been a huge time and energy saver if I’d had the money ($180 for the filter, $350 to just take care of it for you). They are also nice enough to post the instructions for how to do it yourself. How great is the internet?

The one piece of info that they don’t provide is the dimensions of the hot mirror that you need to replace… quite reasonable, since they have it for sale.

Another good site is here:
http://www.abe.msstate.edu/~jwooten/camera/lense.html

actually for the 990, so some of the screws might be different. He gives a dimension for the hot mirror in the 990 of 11mm x 12mm x 2.5mm. This is not quite right for the 995.

I agonized over how to get a piece of really clear glass cut just right. In retrospect, this was dumb. I should have just charged ahead. I finally found a local stained-glass maker who was happy to cut some chips the right size for me… I’d tried myself with a hardware store glass cutter and couldn’t get them just right. She had a much nicer cutter and it took no time to get them perfect.

The camera was a cinch to get apart. The only thing I have to add to the LifePixel site is to watch your screws… they are in several different sizes.

Keep track of which hole these two screws go in... one's black, one's silver, different lengths. I wrote on the case with a pencil.

The other thing is that once I got to the mirror, I could see that it was much thicker than I’d been expecting. The dimensions I measured were
10mm x 11.45 mm x 2.85mm thick. My piece was more like 2.4 mm thick, and had many more options in thicker glass. I’ll probably cut another one and try again.

One thing to notice:

The hot mirror perched above the CCD. It actually sticks to the rubber gasket pretty tightly.


The mirror is sitting on a rubber gasket. Lots of wiggle room for cutting it a bit big (mine was more than 1mm in each direction and it worked fine). The chip is much smaller than the glass, so chips on the edge don’t matter.

Putting it all back together, everything worked fine. There is a little ribbon connector that is a pain in the ass to get back together, but be gentle and patient and it should work. Test the camera before you put all the screws back. This’d be the first place I’d look if there’s trouble.

With a mirror 0.5mm to thin, my focus is a mess. I found that by going into the settings I could tell it that I’d actually put a 3x zoom lens over the camera and this adjusted something in software that seemed to make it focus much better. There is also manual focus, but it sucks. I’ll get a thicker piece of glass.

The pictures have a weird red tint to them. I’ll play more in the daylight and post pictures.